DETERMINING THE MOST IMPACTFUL INVASIVE VEGETATIVE SPECIES ON FRESHWATER SALMON HABITAT IN WESTERN WASHINGTON DURING 2021: USING LITERATURE AND SURVEYING PROFESSIONALS

Item

Title

Eng DETERMINING THE MOST IMPACTFUL INVASIVE VEGETATIVE SPECIES ON FRESHWATER SALMON HABITAT IN WESTERN WASHINGTON DURING 2021: USING LITERATURE AND SURVEYING PROFESSIONALS

Date

Eng 2021

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Eng Kies, Danielle

Identifier

Eng Thesis_MES_2021_Kies

extracted text

DETERMINING THE MOST IMPACTFUL INVASIVE VEGETATIVE SPECIES ON
FRESHWATER SALMON HABITAT IN WESTERN WASHINGTON DURING 2021:
USING LITERATURE AND SURVEYING PROFESSIONALS

by
Danielle Green

A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
May 2021

©2021 by Danielle Green. All rights reserved.

This Thesis for the Master of Environmental Studies Degree
by
Danielle Green

has been approved for
The Evergreen State College
by

________________________
Kathleen Saul, PhD
Member of the Faculty

________________________
Date

ABSTRACT
Determining the Most Impactful Invasive Vegetative Species on Freshwater
Salmon Habitat in Western Washington During 2021: Using Literature and
Surveying Professionals
Danielle Green

Invasive vegetation is a growing problem in Western Washington. As invasive vegetative
species (IVS) proliferate freshwater environments, they negatively impact ecosystems at
an increasing rate. The iconic Pacific salmon (Oncorhynchus spp.) provide significant
economic, environmental, and cultural values in Western Washington. Protecting
dwindling salmon populations is more of a priority than ever before, since many species
groups are currently endangered or threatened. The Salmon have experienced recent
habitat degradation as a direct result of IVS domination and yet IVS has been commonly
overlooked as a factor for salmon population decline. This study surveyed professionals
and synthesized the relevant literature to gain a deeper understanding of IVS impacts on
freshwater salmon habitat. The survey results narrowed down 52 noxious weeds to the
following top four most impactful IVS: knotweed (Fallopia spp.), reed canarygrass
(Phalaris arundinacea), yellow flag iris (Iris pseudacorus), and Brazilian elodea (Egeria
densa). Using criteria derived from previous literature, based on salmon biology and
environmental requirements, these four invasive plants were critiqued on their impacts
towards overall biodiversity, sediment loads, stream chemistry, water flow regimes,
stream temperatures, shelter abundance, migration route obstruction, and predator habitat.
While knotweed and reed canary grass have been generally well-documented in scientific
literature, substantial knowledge gaps appeared in the literature on yellow flag iris and
Brazilian elodea research. Ultimately, the goal is to present this body of work to the
public so that interested parties can collaborate more effectively, thereby enhancing
efforts in Pacific salmon conservation and the fight against invasive species.

Presentation Link: https://arcg.is/1njGC8
Keywords: invasive vegetation, noxious weeds, Pacific salmon, Western Washington,
freshwater habitat, survey, reed canarygrass, yellow iris, Brazilian elodea, knotweed

Table of Contents
List of Figures .................................................................................................................. viii
List of Tables ...................................................................................................................... ix
Glossary ...............................................................................................................................x
Acknowledgements ............................................................................................................ xii
Chapter 1: Introduction ................................................................................................... 1
1.1 Significance of Research......................................................................................... 1
1.2 Statement of Positionality ....................................................................................... 4
1.3 Study Area .............................................................................................................. 5
1.4 Salmon History ....................................................................................................... 7
1.5 Invasive Vegetation History ................................................................................... 9
1.6 Partnerships ........................................................................................................... 11
Chapter 2: Literature Review ........................................................................................ 12
2.1 Salmon Introduction.............................................................................................. 12
2.1.1 Salmon Importance ...................................................................................... 13
2.1.2 Salmon Survival Needs ................................................................................ 17
2.1.3 Salmon Resistance/Resilience ..................................................................... 19
2.2 Invasive Vegetation Introduction .......................................................................... 24
2.2.1 A Growing Problem ..................................................................................... 25
2.2.2 Anthropogenic Impacts ................................................................................ 27
2.2.3 Benefits of IVS ............................................................................................ 27
2.2.4 Disadvantages of IVS .................................................................................. 29
2.2.5 Economic Impact of IVS ............................................................................. 31
2.3 Restoring Salmon Habitat ..................................................................................... 35
2.3.1 Habitat Requirements................................................................................... 35
2.3.1.1 WAC Standards .................................................................................. 35
2.3.2 Human Impacts ............................................................................................ 44
2.3.3 Ownership Boundaries ................................................................................. 50
2.3.4 Habitat Availability ...................................................................................... 51
2.3.5 IVS Potential ................................................................................................ 54
2.4 Stakeholder Relationships..................................................................................... 66
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2.4.1 Communication/Collaboration ..................................................................... 66
2.4.2 Relationships with Salmon .......................................................................... 69
2.4.3 Stakeholders and IVS ................................................................................... 70
2.4.4 Perceptions and Controversies ..................................................................... 70
Chapter 3: Methods ........................................................................................................ 73
3.1 Team ..................................................................................................................... 73
3.2 Survey ................................................................................................................... 74
3.3 Survey Distribution ............................................................................................... 76
3.4 Survey Analysis .................................................................................................... 77
3.5 Mapping ................................................................................................................ 78
Chapter 4: Results & Discussion ................................................................................... 80
4.1 Knotweed (Fallopia spp.) ..................................................................................... 83
4.1.1 Dichotomy.................................................................................................... 86
4.1.2 Overall Biodiversity (Flora, Fauna, Invertebrates) ...................................... 88
4.1.3 Sediment Loads ............................................................................................ 92
4.1.4 Stream Chemistry......................................................................................... 94
4.1.5 Water Flow Regimes.................................................................................... 96
4.1.6 Stream Temperatures ................................................................................... 96
4.1.7 Shelter Abundance (Woody Debris) ............................................................ 97
4.1.8 Migration Route Obstruction ....................................................................... 98
4.1.9 Predator Habitat ......................................................................................... 100
4.2 Reed canarygrass (Phalaris arundinacea) .......................................................... 100
4.2.1 Dichotomy.................................................................................................. 104
4.2.2 Overall Biodiversity (Flora, Fauna, Invertebrates) .................................... 104
4.2.3 Sediment Loads .......................................................................................... 108
4.2.4 Stream Chemistry....................................................................................... 108
4.2.5 Water Flow Regimes.................................................................................. 112
4.2.6 Stream Temperatures ................................................................................. 114
4.2.7 Shelter Abundance (Woody Debris) .......................................................... 114
4.2.8 Migration Route Obstruction ..................................................................... 115
4.2.9 Predator Habitat ......................................................................................... 115
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4.3 Yellow flag iris (Iris pseudacorus) ..................................................................... 116
4.3.1 Dichotomy.................................................................................................. 120
4.3.2 Overall Biodiversity (Flora, Fauna, Invertebrates) .................................... 120
4.3.3 Sediment Loads .......................................................................................... 123
4.3.4 Stream Chemistry....................................................................................... 124
4.3.5 Water Flow Regimes.................................................................................. 127
4.3.6 Stream Temperatures ................................................................................. 128
4.3.7 Shelter Abundance (Woody Debris) .......................................................... 128
4.3.8 Migration Route Obstruction ..................................................................... 129
4.3.9 Predator Habitat ......................................................................................... 129
4.4 Brazilian elodea (Egeria densa).......................................................................... 130
4.4.1 Dichotomy.................................................................................................. 134
4.4.2 Overall Biodiversity (Flora, Fauna, Invertebrates) .................................... 135
4.4.3 Sediment Loads .......................................................................................... 139
4.4.4 Stream Chemistry....................................................................................... 140
4.4.5 Water Flow Regimes.................................................................................. 144
4.4.6 Stream Temperatures ................................................................................. 146
4.4.7 Shelter Abundance (Woody Debris) .......................................................... 146
4.4.8 Migration Route Obstruction ..................................................................... 146
4.4.9 Predator Habitat ......................................................................................... 148
Chapter 5: Conclusion .................................................................................................. 148
5.1 Thesis Recap ....................................................................................................... 149
5.2 IVS Management ................................................................................................ 151
5.3 Next Steps ........................................................................................................... 152
Bibliography ............................................................................................................. 156
Appendices ................................................................................................................ 189
Appendix A: Survey Part I .............................................................................................. 189
Appendix B: Species List ................................................................................................. 194
Appendix C: Survey Part II ............................................................................................. 195
Appendix D: Survey Part III ........................................................................................... 196
Appendix E: Study Maps ................................................................................................. 197
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Appendix E1: Study Area of Western WA Counties

197

Appendix E2: Western WA Chinook Streams

198

Appendix E3: Western WA Chum Streams

199

Appendix E4: Western WA Coho Streams

200

Appendix E5: Western WA Pink Streams

201

Appendix E6: Western WA Sockeye Streams

202

Appendix E7: Western WA Steelhead Streams

203

Appendix E8: Top Four IVS Locations

204

Appendix E9: IVS Presence on Chinook Streams

205

Appendix E10: IVS Presence on Chum Streams

206

Appendix E11: IVS Presence on Coho Streams

208

Appendix E12: IVS Presence on Pink Streams

209

Appendix E13: IVS Presence on Sockeye Streams

210

Appendix E14: IVS Presence on Steelhead Streams

211

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List of Figures
Figure 1: Non-indigenous ranking of taxonomic groups in PNW. ............................... 3
Figure 2: Ecosystem services of Pacific salmon ............................................................. 9
Figure 3: An example of the salmon nutrient pulse ..................................................... 15
Figure 4: Effects of temperature on salmonids ............................................................ 18
Figure 5: The invasion curve ......................................................................................... 32
Figure 6: DWD placement simulation........................................................................... 42
Figure 7: Riparian zone quality at various urbanization levels ................................. 48
Figure 8: Chinook size variances across two habitat types ......................................... 65
Figure 9: [photo] Knotweed leaf identification ............................................................ 84
Figure 10: [photo] Japanese knotweed identifiers ....................................................... 85
Figure 11: Knotweed influences on the food web ........................................................ 91
Figure 12: Knotweed N resorption prior to litterfall. .................................................. 95
Figure 13: [photo] Knotweed-induced erosion ............................................................. 99
Figure 14: [photo] Reed canarygrass identification drawing ................................... 103
Figure 15: [photo] Reed canarygrass identifying photos .......................................... 103
Figure 16: [photo] Northern pike stomach contents .................................................. 116
Figure 17: [photo] yellow flag iris flower .................................................................... 118
Figure 18: [photo] Yellow flag iris identification drawing ........................................ 119
Figure 19: [photo] Yellow flag iris proliferation ........................................................ 119
Figure 20: Chemical Compounds Within Tissues of Multiple Iris Sp. .................... 125
Figure 21: [photo] Egeria densa identification drawing ........................................... 132
Figure 22: [photo] Comparison drawing of Hydrilla, Elodea, and Egeria .............. 133
Figure 23: [photo] Brazilian elodea in flower............................................................. 133
Figure 24: [photo] Egeria densa proliferation............................................................ 134
Figure 25: Stages of IVS management ........................................................................ 152
Figure 26: [photo] Invasive Species Application Reporting ..................................... 154

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List of Tables
Table 1: Top invasive species detections by county ....................................................... 7
Table 2: Criteria for assessing IVS impacts on salmon in WA................................... 19
Table 3: Physical Parameters of Lotic Waters ............................................................. 39
Table 4: Survey Results and Ranking of top IVS ........................................................ 80
Table 5: Percentage of available research by species .................................................. 80
Table 6: Top IVS within 200 feet of salmon streams ................................................... 82

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Glossary
Allochthonous: Originating or formed in a place other than where found (Braatne et al.,
2007; Custer et al., 2017)
Anadromous: (of a fish such as the salmon) migrating up rivers from the sea to spawn.
The opposite of catadromous (1Oxford English Dictionary, n.d.).
Andisols: soils derived from glass, pumice, and short-range minerals (Bockheim et al.,
2014).
Anthropochory: The dispersal of seeds, spores, or fruit by humans (1Definitions.net,
n.d.).
Epilimnion: The upper layer of water in a stratified lake (2Oxford English Dictionary,
n.d.).
Hydrochory: The dispersal of seeds, spores, or fruit by water (2Definitions.net, n.d.).
Hypolimnion: The lower layer of water in a stratified lake, typically cooler than the
water above and relatively stagnant (3Oxford English Dictionary, n.d.).
Invasion Ecology (aka Invasion Biology): the study of the establishment, spread, and
ecological impact of species translocated from one region or continent to another by
humans (Sol, 2001 as cited in Henderson et al., 2006).
Invasive Vegetative Species (IVS): any foreign/alien/non-native vegetation brought
over from other regions of origin since European colonization of the United States, both
intentionally and unintentionally, that cause human, environmental, or economic harm
and has the ability to rapidly spread and reproduce, are characteristically adaptable,
have a broad niche, appear aggressive, and are typically r-selected species. ‘Invasive
vegetative species’ does not include intentionally planted agronomic crops or nonharmful exotic organisms (Executive Order 13112 - 1. Definitions). *The terms Invasive
Vegetative Species and Noxious Weeds are synonymous.
Lacustrine: Relating to or associated with lakes (4Oxford English Dictionary, n.d.).
Lentic: (of organisms or habitats) inhabiting or situated in still fresh water (5Oxford
English Dictionary, n.d.).
Lotic: (of organisms or habitats) inhabiting or situated in rapidly moving fresh water
(6Oxford English Dictionary, n.d.).
North-of-Falcon (NOF): public planning forum in which federal, state and tribal fish
managers meet in tandem with PFMC deliberations on ocean seasons, to set recreational
and commercial salmon fisheries for waters within three miles of the coast of Washington
and northern Oregon, as well as Puget Sound. The North of Falcon season setting
process occurs in a series of public meetings each spring, attended by federal, state,
tribal and commercial fishing industry representatives and concerned citizens. (Iverson,
2008). For more information visit: https://wdfw.wa.gov/fishing/management/north-falcon
Nutritional Pulses: “Pulses are a low-fat source of protein with high levels of protein
and fibre [sic]. Pulses also contain important vitamins and minerals like iron, potassium
and folate [sic].” (Global Pulse Confederation [GPC], n.d.).
x

Oligotrophic: “(of lakes and similar habitats) poor in nutrients and plant life and rich in
oxygen: Compare eutrophic.” (Dictionary.com, n.d.)
Phenotypic plasticity: Phenotypic plasticity is the ability of the same genotype to
produce a different phenotype under different environmental conditions (Waples et al.,
2009).
Phytomining: “the production of a `crop' of a metal by growing high-biomass plants
that accumulate high metal concentrations” (Brooks et al., 1998).
Population (in reference to salmon): “a scientifically designated, biologically distinct
group of individuals (e.g., Lower Columbia River Spring Chinook, Skagit River coho)
adapted to life in the special conditions of our state's rivers and estuaries” (Washington
Department of Fish and Wildlife [WDFW], 2011).
Resilience: “the amount of disturbance that an ecosystem can accommodate without
shifting to a different regime or stability domain as characterized by a fundamentally
different structure, function, and feedback mechanisms” (Walker et al., 2004, as cited in
Bottom et al., 2009, introduction section).
Response diversity: “Variation in response to environmental change among species with
the same ecosystem function” (Elmqvist et al., 2003, abstract). “Diverse life histories
within and among Pacific salmon species are a population-level example of response
diversity” (Bottom, et al., 2009, response diversity section).
Salmon ecosystem: “an integrated system of people and environments that are directly
linked to anadromous salmon populations or groups of populations within geographic
areas” (Bottom et al., 2009, introduction section).
Salmon ecosystem resilience: “…a measure of whether this integrated and adaptive
system can reorganize, renew, and persist following disturbance” (Bottom et al., 2009,
introduction section).
Semelparity: the reproductive process that includes death soon after mating (Quinn,
2005).
Stakeholder: any individual/entity that has an interest or concern about the health of the
environment; including residents, such as animals, plants, micro- and macro- organisms,
etc. The word stakeholder, in the context of this thesis, is synonymous with ‘concerned
party’, be it an agency, company, group, or individual. Therefore, the term stakeholders,
in this sense, align with the parties who are affected by the economics, environmental
impacts, political implications, public health impacts, etc. of activities related to Pacific
salmon and/or invasive vegetation.

xi

Acknowledgements
I would like to give special thanks to my thesis reader Kathleen Saul, PhD for all of your
wonderful edits and cheerleading to keep me moving forward. I would also like to thank a few more MES
faculty, such as Shawn Hazboun, PhD for providing early help with the creation of my survey, John
Withey, PhD for helping me to get started early and with the thesis design, to Mike Ruth for all of his
shared GIS wisdom, as well as the rest of the MES faculty for all of their support & inspiration throughout
my thesis journey. Furthermore, I would love to send a special thanks to a few of my peers, such as Alexis
Haifley and Jessica Converse whose peer edits over the months were invaluable, Tyler Cowdrey whose
extra help in GIS was also highly valued, as well as Angela Dillon who provided a deeper insight into tribal
cultures and answered many of my fish related questions.
I would also like to extend thanks to Justin Bush, coordinator of the WA Invasive Species Council
for providing the original idea to this thesis and for introducing me to other professionals who also
provided help in this project. Thank you, Mary Fee with the Washington State Noxious Weed Control
Board, for all of your quick email responses and help creating and distributing the survey on
SurveyMonkey. I would also like to extend thanks to the rest of the “thesis team” as detailed further in
Chapter 3: Team, for all of your extra help with editing, moving forward, and additional insight to
noxious weeds and their impacts on salmon habitat.
Furthermore, I would like to thank the Green River College Natural Resources Department, both
the faculty and students for helping provide my base knowledge and supporting me through this, especially
Monica Paulson Priebe, PhD, Rob Sjogren, Holly Nay, Gene McCaul, Chuck Wytko, and Samantha
Thompson.
Also, I certainly could not have made it through without the continual loving support of my life
partner Jesse Chester and for my beautiful daughter Alexandrea Kies who continues to be my inspiration
and motivation in life no matter how far we are from each other.
The Road Not Taken
Robert Frost (1874-1963)
Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;
Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,
And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.

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Chapter 1: Introduction
This thesis project answers the question, which invasive vegetative species have
the greatest negative impact on Western Washington’s freshwater salmon habitat in 2021
by using literature and surveying professionals. To best implement such a topic, I have
broken up the thesis into chapters. Chapter 1 will include the significance of this
research, my statement of positionality, an overview of the study area, a brief history on
salmon and invasive vegetation, and a look at the partnerships involved. Chapter 2
consists of an extensive literature review on salmon, invasive vegetation, salmon habitat,
and stakeholder relationships; each of these will have their own sub-sections as well.
Chapter 3 encompasses the methods used for this thesis. Chapter 4 covers the results
and discussion from both the literature as well as a survey completed by field
professionals, going into detail on each of the top species and their potential impacts to
salmon habitat. Finally, Chapter 5 provides the conclusion for this thesis, forms logical
correlations between the topmost impactful invasive vegetative species and Pacific
salmon habitat, and recommends future research where knowledge gaps may exist.
References made within the text to various sections of this thesis, such as Chapters,
Figures, Tables, Appendices, etc. will be in bold font. Furthermore, this thesis does not
discern between “wild” or hatchery populations of salmon as the focus is on habitat,
which both populations use.

1.1 Significance of Research
Studies indicate that salmon have been extirpated from approximately 40% of
their historic range in the Pacific Northwest (Stark, n.d.; Zemek, 2019). As keystone
species, these animals persist as vital importance to the ecosystems in which they exist.

1

Salmon facilitate several natural processes, such as providing a primary seasonal food
source to many predatory species of fauna, including orcas, bears, raptors, and others,
deposition of marine nutrients into terrestrial environments, and by regulating
macroinvertebrate populations. Past experimentation has taught ecologists and
conservationists that abrupt removal of a keystone species has generally precipitated
catastrophic collapse of its native ecosystem (Mills et al., 1993). Public outcry from
ecologists, environmental professionals, indigenous communities, and the general public
has encouraged salmon recovery programs and preservation of this iconic species.
Plants are taxonomic group with the highest abundance for non-indigenous
species in Washington, Oregon, and Idaho (Figure 1) (Sanderson et al., 2009). Since the
advent of invasion ecology, around the turn of the millennia, there has been a growing
body of evidence which points to invasive vegetation as a contributing factor in salmon
habitat degradation. The implications of invasive vegetative species on the health of
Pacific salmon habitat have not been thoroughly studied. However, it remains imperative
that science ultimately quantify these effects so that environmental agencies, ecological
organizations, and conservation groups possess the knowledge necessary to confront the
looming crisis of Pacific salmon population decline.

2

Figure 1: Non-indigenous ranking of taxonomic groups in PNW.
Plants are the highest-ranking taxonomic group for most species non-indigenous to Washington (WA), Oregon (OR), and Idaho (ID)
(Sanderson et al., 2009, Figure 3).

Salmon have continued to be especially sensitive to various environmental
conditions, including overall biodiversity (such as macroinvertebrate and flora
populations), sediment loads, stream chemistry (such as DO and pH), water flow regimes,
stream temperatures, shelter abundance (such as down woody debris (DWD)), migration
route obstruction, and predator habitat. As of yet, there is not significant research into
how certain types of IVS impact each of these factors. This study only addresses the
highest priority invasive vegetative species and their inherent impacts to salmon habitat.
Not only is this thesis taking on a novel concept by relating invasive vegetation and their
specific ecological impacts to salmon habitat, but by narrowing the focus to such precise
conditions, as well as compiling all of the information into a single document, will better
allow various agencies to efficiently combine efforts and resources. An interdisciplinary

3

approach will be necessary to effectively apply these findings to a salmon habitat
management strategy.

1.2 Statement of Positionality
Growing up as a natural born American white female I no doubt had privilege, but
that was often obscured by my rough upbringing. As a result, I tended to gravitate more
towards nature for companionship while hiding from the human world. I owe a lot of who
I am to mother nature, especially as somebody who grew up without a mother of my own.
I have had to overcome many personal struggles; of which, I always seemed to gravitate
towards nature to heal myself… or for safer shelter.
While attending Green River College (GRC) in the Natural Resource Department,
I was able to attain four associate of applied science degrees, including Associate of
Applied Science (AAS) degrees in the fields of 1) Forestry, 2) Geographic Information
System (GIS), 3) Park Management, and 4) Water Quality, as well as one Bachelor of
Applied Science (BAS) degree in Forest Resource Management. I was also a tutor for
many of my classes, as I have a strong passion for helping others. Furthermore, I was a
guest speaker multiple times, and later an adjunct instructor, for the five-credit class:
‘Bio-Invasions: Invasive Species Management’ class (NATRS 386).
During my graduate course at The Evergreen State College (TESC), I focused all
of my assignments around the topic of ‘invasion ecology’ and thus began working on this
thesis. Because of my background, I see invasive vegetation as the “bullies” of the
vegetation world. I strongly believe that invasive vegetative species (IVS), when in their
natural environment, can shine with all their glory and be admired for all of which they
provide; but as the saying goes, ‘there exists a time and place for everything’; and in
4

many habitats IVS are definitely out of place. For instance, I acknowledge that
Himalayan blackberry (Rubus bifrons) provides nutritional value as delicious antioxidantrich aggregate fruits. I also understand that while in North America, this blackberry
constantly “bullies” its native counterpart, by outcompeting for available resources,
reproducing vigorously, and depleting soil nutrients. Throughout my academic career I
have seen ample evidence for a need to manage noxious weeds in order to preserve the
majestic native ecosystems of Western Washington.

1.3 Study Area
Western Washington consists of a diverse landscape situated between the Puget
Sound lowlands and the Pacific Ocean to the west and stretches to the high elevation
peaks of the Cascade Mountain Range to the east. The historic ecological composition of
the Pacific Northwest (PNW) is dominated by sprawling mixed forests of conifer and
deciduous tree species. The dominant soils of Western Washington originate from
igneous parent material deposited from marine encroachment, glacial activities, and
volcanic processes (Littke et al., 2011). These primary Andisols, created by the tectonic
process of subduction and seismic uplift, as well as the upwelling of molten material
under the North American plate, form the foundation of diverse ecology in Western
Washington (Pazzaglia & Brandon, 2001; Brockway, 1998). Washington has a temperate
climate, due to its latitudinal position between the 46° and 49° parallels (Western
Regional Climate Center [WRCC], n.d.). Precipitation falls as both rain and snow;
although, the mountains accumulate most of the snowfall. A single year’s maximum
rainfall intensities, out of a ten-year period, can be as much as one inch in a single hour or
up to seven inches over twelve hours, with the higher intensities occurring along the
5

windward slopes of the mountains (WRCC, n.d.). Thunderstorms and hailstorms have
been infrequent to Western Washington (WRCC, n.d.). Monthly sunshine can average
“from approximately 25 percent in winter to 60 percent in summer” (WRCC, n.d.,
Western Washington section). The 19 counties situated within this study area (Appendix
E1) include: Clallam, Clark, Cowlitz, Grays Harbor, Island, Jefferson, King, Kitsap,
Lewis, Mason, Pacific, Pierce, San Juan, Skagit, Skamania, Snohomish, Thurston,
Wahkiakum, and Whatcom.
Using stream data collected from the Department of Natural Resources, there
exists an estimated total of over 164,000 miles of streams within Western Washington.
Of these streams roughly 24%, are Type F, also known as fish-bearing streams. Fishbearing streams were calculated from the water-courses shapefile on WA DNR's Open
GIS Data Portal. According to the Washington Department of Fish and Wildlife
(WDFW), “There are eight species of native “salmonids” in Washington [and]
approximately 486 known “populations””: Chinook (Oncorhynchus tshawytscha)
(Appendix E2), Chum (O. keta) (Appendix E3), Coho (O. kisutch) (Appendix E4), Pink
(O. gorbuscha) (Appendix E5), Sockeye (O. nerka) (Appendix E6), Steelhead (O.
mykiss) (Appendix E7), Bull Trout (Salvelinus confluentus), and Cutthroat (O. clarkii)
(WDFW, 2011). Of these eight, only the first six mentioned will be the focus of this
thesis.
According to data downloaded from EDDMapS, there have been 600 total
locations where the top four invasive species have been observed throughout the 19
Western Washington counties (see Table 1 and Appendix E8) (University of Georgia
Center for Invasive Species and Ecosystem Health [UGCISEH], 2020). When search

6

parameters are limited to a 200-foot buffer between IVS and salmon stream segments, all
four of the IVS appear within 120 locations across 17 of the 19 counties; which are
further detailed in Chapter 4. EDDMapS is further explained in Chapter 3.4.
Table 1: Top invasive species detections by county
Unfiltered county populations of knotweed, reedcanary grass, yellow flag iris, and Brazilian elodea
(Data generated from EDDMapS). Table 1 is sorted by highest to lowest totals per county.

1.4 Salmon History
With salmon populations on the decline, any effort to protect salmon requires
immediate implementation. Today, 14 salmon species groups have been listed under the
Endangered Species Act (Governor’s Salmon Recovery Office [GSRO] et al., 2021). Of
these 14, five salmon species groups remain in crisis; including: three Chinook (Puget
Sound, Upper Columbia River Spring, and Snake River Spring/Summer), one Sockeye
(Lake Ozette), and one Steelhead (Puget Sound) (GSRO et al., 2021). Also, five species
groups continually struggle to recover; such as: one Coho (Lower Columbia), one
7

Chinook (Lower Columbia River), two Steelhead (Upper and Middle Columbia River),
and one Chum (Columbia River) (GSRO et al., 2021). However, four groups have been
making progress and approaching the recovery goals set in place by The National
Oceanic Atmospheric Administration (NOAA); these consist of: two Steelhead (Snake
River Basin and Lower Columbia River), one Chum (Hood Canal Summer Run), and one
Chinook (Snake River Fall Run) (GSRO et al., 2021). The information on these species
has been established based on adult “wild” stocks, lacks complete data, and that is not
meant to replace NOAA’s status review.
Salmon act as a keystone species and are known to play an important role in the
trophic web, both as predator and prey. Salmon also provide many ecosystem services as
illustrated in Figure 2 (Bottom et al., 2009). Additionally, after returning to natal
streams, their carcasses deliver important marine nutrients (such as nitrogen, sulfur, and
carbon) as well as salinity into forestlands, prairies, and other ecosystems that would
otherwise be deprived of these nutrients (Rahr, 2019). Moreover, salmon continue to be
vital to our economy. According to the Washington Department of Fish and Wildlife
(WDFW) Conservation website, Salmon fishing contributes approximately $175 million
yearly to Washington State’s economy while it provides recreational activities to 150,000
anglers and enables the continuation of several crucial tribal traditions (Washington
Department of Fish and Wildlife [WDFW], n.d.). Furthermore, salmon persist as a major
food source for another endangered species, the Southern Resident Orca. Thus,
improving essential salmon habitat could have positive effects on the survival of many
species.

8

Figure 2: Ecosystem services of Pacific salmon
“Local salmon populations provide provisioning, cultural, and supporting ecosystem services that benefit people. These services often
involve two-way interactions with feedbacks to salmon. Because salmon populations are sensitive to changes in environmental quality
and habitat structure, they also are indicators of important regulating services that people derive from resilient salmon ecosystems.”
(redrawn from Bottom et al., 2009, Figure 2). The quote was taken directly from Bottom et al., 2009, Figure 2.

1.5 Invasive Vegetation History
Starting around 1845, Charles Darwin made the first mention to the potential
awareness of invasive species (Henderson et al., 2006). The first weed law, according to
the Noxious Weed Control Board (NWCB), passed in 1881 to combat the establishment
of Canada thistle (Cirsium arvense) (Washington State Noxious Weed Control Board
[NWCB], n.d.). In the late 1960’s legislature established the Washington Noxious Weed
Control Board (NWCB, n.d.). Later, the Global Invasive Species Programme (GISP) of
1997 (Henderson et al., 2006) formed. Then, in 1999, former President Bill Clinton
passed Executive Order 13112, which created the National Invasive Species Council
(NISC) and further promoted a need for management and control.
Invasive vegetative species (IVS) have been a substantial element of the
anthropogenic changes to the natural systems of this planet. As of 2004, across the United
9

States, invasive plants covered roughly 133 million acres and persist with an estimated
1.7 million-acre spread per year (US Forest Service [USFS], 2004). Moreover, IVS can
be seen just about anywhere. They remain present in and around cities and along highway
corridors, such as where the frequency of soil disturbance becomes higher (Hansen &
Clevenger, 2005) and where the density of humans increases (Spear et al., 2013). IVS
cause varying levels of damage, such as reduction in local biodiversity, infiltration of
municipal water systems, damage to infrastructure, reduced productivity of agricultural
land, and depreciation of property value. IVS also require significant financial resources
to manage as well as to maintain recovered areas; for instance, both rush skeletonweed
(Chondrilla juncea) and Scotch broom (Cytisus scoparius) each cost Washington over
$140 million annually to manage (Community Attributes Inc. [CAI], 2017). These costs
only increase over time, as the species becomes more established in an area, as illustrated
in Figure 5.
Invasive vegetation has the potential to dramatically affect salmon habitat, due to
the biological sensitivity of salmonids to environmental changes, which become
compounded by climate change and human influences (Bisson et al., 2009). By
understanding the impact of invasive noxious weeds on salmon habitat, various
conservation and ecological organizations/agencies/etc. will be able to better collaborate
management efforts with salmon conservationists. This collaboration will allow for these
various groups to combine efforts, time, money, and resources in a way that will lead to
possible eradication of high priority invasive species. Eradicating the most impactful
species will also increase the salmon recovery and enhancement efforts.

10

To best investigate such a thesis topic, an extensive literature review assessing
each invasive species based on various environmental criteria will be needed (Chapter
2). This literature review will be used to assess the framework as well as history of both
IVS and salmon. The review will also provide a deeper look into the relationships
between each of the stakeholders. Stakeholders include Pacific salmon species, Western
WA tribal nations, private landowners, businesses, environmental conservationists,
invasive vegetation, and the ecosystem. Although the non-human stakeholders do not
communicate in the traditional sense, their rights to a healthy environment are no less
important and thus need to be advocated for.

1.6 Partnerships
The range of stakeholders regarding salmon habitat conservation is essentially
limitless. The interconnectedness that human society shares with Pacific salmon is
significantly widespread, and applies to all social positions, demographics, and
professional affiliations. For instance, private landowners are concerned with property
value, which may decrease as a result of poor land management policies regarding
salmon habitat, i.e., water quality, local ecosystem health, environmental regulations, etc.
Business entities may be impacted by restrictions imposed on their operational capacity
due to legislative mandates involving salmon habitat conservation. Environmental
activists see the need to protect salmon as a means to preserve the natural function of the
ecosystem. Some individuals derive a sense of cultural identity from Pacific salmon, such
as indigenous peoples, and feel that the fight for these iconic fish species has been a fight
for their history. This topic gets covered in more depth in Chapter 2.4.

11

Chapter 2: Literature Review
This literature review serves as the first step in determining the top four most
impactful Invasive Vegetative Species (IVS) in freshwater salmon habitat within Western
Washington. Presented from the viewpoint of a western science ecologist, this review
takes on a broad approach to answer the question: Which invasive vegetative species
(IVS) have the most impact on freshwater salmon habitat in Western Washington from
the perspective of current field professionals and literature during 2021? Because
managing for invasive vegetation can be a controversial topic, this literature review will
present a wide range of stances on that subject matter.
This literature review will address four main topics: 1) Pacific salmon species,
while sensitive to environmental factors, play a key role in Western Washington’s
ecosystem and within society, due to their environmental, cultural, and economic
importance; 2) invasive vegetation, despite any potential benefits, has become a serious
concern in Western Washington; 3) invasive vegetation affects salmon habitat,
contributing further to the decline of salmon populations; as well as 4) interagency
communication and collaboration, though improving, still poses challenges to efficient
management of freshwater systems.

2.1 Salmon Introduction
Pacific salmon, Oncorhyncus spp., belong to the salmonid family. Six commonly
identified species of true anadromous Pacific salmon include: Sockeye (O. nerka), Coho
(O. kisutch), Chum (O. keta), Chinook (O. tshawytscha), Pink (O. gorbuscha), and
Steelhead (O. mykiss). Sub-populations of salmon[-;]’ can reject the instinct to migrate to
sea; some of these include kokanee trout, a non-migrating version of sockeye salmon;
12

rainbow trout, a non-migrating version of steelhead; and cutthroat trout. These resident
populations spend all their life stages in freshwater environments. The focus of this thesis
pertains to freshwater habitat.
All Pacific salmon start their life cycle as an egg that had been deposited in a
gravel nest, also known as a ‘redd’, excavated by the female fish, and fertilized by a male
in a freshwater stream. Two to three months after fertilization, it emerges as a hatchling,
or ‘alevin’, with an external yolk sac (BiologyWise.com, 2010; Quinn, 2005). Once the
alevin has fully metabolized the yolk sac, it exits the redd and begins the salmon life
stage known as ‘fry’, colloquially referred to as fingerlings. Migration typically occurs
when the salmon are one to two years old, though this varies by species and
environmental cues (National Park Service, 2019). The anadromous fish will feed and
mature at sea for several years (Quinn, 2005); however, this thesis does not focus on
marine habitat. Once they have developed enough and assimilated the appropriate amount
of nutrients, they begin the arduous migration back to their natal waters (Groot &
Margolis, 1991). Salmon are semelparous, once they reach their natal spawning grounds,
they reproduce and then die. Theoretically, certain species of noxious weeds may only
affect distinct stages in a salmon’s life cycle. Knowing these various stages and the needs
of salmon within each, can better determine the level and rate of effects by IVS.

2.1.1 Salmon Importance
The vital importance of Pacific salmon to Washington’s environment, cultural
identity, economy, and public health has been well-established (Bottom et al., 2009;
Close, 2015; Colombi, 2012; Cronin & Ostergren, 2007). Many of the freshwater streams
in the Pacific Northwest exist as oligotrophic environments (Olympic National Park,
13

2015). The annual return, death, and subsequent decomposition of salmon contributes a
rich nutrient dump on which many organisms depend (Dillon, 2020).
The salmon-derived nutrient pulse, especially N, plays such an important part in
the trophic web (Figure 3), that environmental restorationists often place their carcasses
within and around streams (Bisson et al., 2009). For instance, in their 2002 study,
Hocking and Reimchen noted that many organisms depend on the salmon’s annual
migration to meet their own protein and nutrient demands. After spawning, decaying
salmon carcasses provide substantial nutrient inputs to riparian vegetation and larger food
webs. Hocking and Reimchen also mentioned that research studies tended to focus on
vegetational uses of salmon nutrients, suggesting that macro-invertebrates of coastal
coniferous forests of the Pacific Northwest, such as spiders, insects, worms, etc., should
be considered as highly important in this ecosystem process (2002).

14

Figure 3: An example of the salmon nutrient pulse
“Schematic of major dispersal pathways for salmon-derived materials during the course of spawning. On the left is the “recycling”
pathway and on the right is the “direct consumption” pathway. Boxes beneath the derived products of feeding pathways suggest
changes in the importance of various components as spawning progresses and tissue chemistry and consumers change. Relative
proportions are not to scale; they are simply suggestive of trends.” (Gende et al., 2002, Figure 3).

Macroinvertebrate communities respond to salmon spawning and subsequent
nutrient enrichment. During salmon spawning in the Snoqualmie River and Kennedy
Creek in Washington State, aquatic invertebrate abundance declined; however, when
salmon carcass decomposition began, invertebrate densities increased two-fold or greater
compared to control reaches (Cederholm et al., 1999). Another 2002 study was conducted
on six coastal watersheds in western British Columbia, in which the researchers
correlated the presence of certain marine derived nutrients, C13 and N15, within the
riparian ecosystem with salmon abundance (Reimchen et al.). Several organic samples
had been extracted from the riparian environments of each of the six locations, then
15

processed and analyzed in a laboratory facility (Reimchen et al., 2002). The samples
analyzed included tree tissue, vegetation foliage, invertebrates, and soil (Reimchen et al.,
2002). Reimchen, Mathewson, Hocking, Moran, and Harris (2002) determined that
concentrations of N15 were much higher in riparian areas with salmon presence when
compared to riparian areas with an absence of salmon.
Furthermore, several large predatory fauna species derive a significant portion of
their total annual nutritional requirements from the seasonal salmon runs. For instance,
black (Ursus americanus), brown (Ursus arctos), and grizzly (Ursus arctos horribilis)
bears often become primarily piscivorous during abundant salmon runs (Quinn, 2005),
relying on the fish to supply them with adequate caloric mass to hibernate over winter. In
British Columbia, foraging bears have been documented moving more than half to nearly
all of the salmon biomass onto land, including as far inland as hundreds of meters,
equivalent to multiple football fields, all the while redistributing vital nutrients through
their urine and feces (Gende et al., 2002). The direct correlation of American Bald Eagle
(Haliaeetus leucocephalus) populations to salmon migration has been well documented
in the Pacific Northwest (Dillon, 2020). In fact, a 2018 study of the Skagit River showed
that chum populations appeared to show parallelism with bald eagle populations
(Rubenstein et al., 2019). Additionally, the orca (Orcinus orca), another iconic species of
the Pacific Northwest, has a life-history intertwined with the fate of salmon. The current
vulnerability of the resident orca population can be attributed to the depletion of wild
salmon numbers (Lucas, 2009).
The indigenous peoples of the Pacific Northwest have relied heavily on wild
salmon for subsistence, cultural purposes, and economic stability since time immemorial

16

(Blumm, 2017; Brown & Footen, 2010; Colombi, 2012). To indigenous tribes, salmon
provide more than recreational activities and nutritious food. Tribal citizens celebrate
salmon and sing about them in traditional ceremonies (Columbia River Inter-Tribal Fish
Commission [CRITFC], 2016). Salmon have also been a primary food staple for more
than 7,000 years (Cannon & Yang, 2006) and once acted as the source of a flourishing
economy for the native peoples (CRITFC, 2016). Horace Axtell, a Nimiipuu elder
tribesman, said this, “[t]he most important element we have in way of life is water. The
next most important element is the fish…” (Colombi, 2012, p75).

2.1.2 Salmon Survival Needs
Knowing what key environmental factors influence healthy salmon populations at
various life stages (Figure 4) will give insight into the criteria that could be used to
assess the impacts of noxious weeds on freshwater salmon habitat. In his 2015 thesis,
Salmon Habitat Loss and Hatchery Dependence: A Case Study of Chambers Creek,
Washington, Julian Close explained the needs of salmon as they progress through their
many stages towards adulthood (Close, 2015). For instance, rainbow trout/steelhead
larvae prefer ambient temperatures near 19°C (66.2°F), and juveniles fair better in cooler
temperatures around 13°C (55.4°F) (Sauter et al., 2001, P. 14). Furthermore, a 2009 study
on coho, steelhead, chinook, and chum combined data on all four species from egg to fry
stages and found that higher levels of very small sand/silt particles in the riverbed
(“fines”) decreased the odds of survival by about 17% (Jensen et al.). Once hatched,
alevin retreat to the crevices of specific gravel substrate, unobstructed by fine sediment
(Close, 2015). Anoxic conditions are fatal to salmon, but the more frequent sub-lethal
effects of low DO concentrations can cause various biological impairments, such as
17

impacts to growth and development, reduced nutritional intake, and a decrease in
swimming performance and efficient upstream migration (Fellman et al., 2015).

Figure 4: Effects of temperature on salmonids
“General biological effects of temperature on salmonids in relation to duration and magnitude of temperature” (Sullivan et al., 2000,
Figure 2.1).

As salmon age into fry, they require a healthy supply of food, such as macroinvertebrates, and plenty of shelter from predators, which DWD provides (Close, 2015).
The existence of DWD in streams creates low-velocity wakes behind structures and high
velocity flow adjacent to the structures. This flow rate variation promotes a faster growth
potential in juvenile salmon, as they minimize energy expenditure in low-velocity zones
and have access to a greater invertebrate drift supply in the adjacent high velocity zones
(Hafs, et al., 2014). All salmon species require clean freshwater habitat uncontaminated
by chemical, biological, or industrial waste. Mcintyre et al. (2018) performed an
extensive study on the effects of toxic stormwater runoff on coho and chum and
determined that chemical pollutants contribute greatly to the decline of the species.
Warming temperatures have been a contributing factor of salmon mortality during both
18

sea-bound and homing runs and have possibly resulted in some straying patterns
(Fellman et al., 2015; Keefer et al., 2019).
Based on the literature reviewed, the criteria used in this thesis to assess IVS
effects on salmon survival needs will include impacts to overall biodiversity, sediment
loads, stream chemistry, water flow regimes, stream temperatures, shelter abundance,
migration route obstruction, and predator habitat. Many of these criteria will come from
WAC 173-201A-200 for fresh water designated uses and criteria (Table 2) (Washington
Administrative Code [WAC], 2020).
Table 2: Criteria for assessing IVS impacts on salmon in WA.
Various tables within WAC 173-201A-200 for fresh water designated uses and criteria and centered around the category for salmonid
spawning, rearing, and migration (WAC, 2020).

2.1.3 Salmon Resistance/Resilience
“Ecologists have often used resilience to refer to … the ability of a biological
system to return to equilibrium after a perturbation” (Waples et al., 2009, p. 1). With
regards to the habitat of Pacific salmon, resiliency reflects its ability to rebound from its
current vulnerable state. Elements to be considered must include factors occurring outside
of the historic context of Pacific salmon ecosystems, such as anthropogenic effects,
19

climate change, and urbanization (Waples et al., 2009). Modern predictive climate
models provide an invaluable tool in estimating the long-term resiliency of salmon
habitat. Zhang et al. proposed that the effects of climate change on salmon might be
better suited as a nonlinear response rather than classifying the effects as either suitable
or lethal, as linear models might fail to fully capture the adaptive nature of living
organisms to respond to their physical environment (2019). By comparing climate
predictions, such as precipitation and temperature, to the suitable ranges of salmon
species, an accurate assessment of species vulnerability can be established.
The success of Pacific salmon depends equally upon ecosystem resiliency and
species resiliency. Resiliency at the ecosystem level allows for ecological process to
reorganize, renew, and persist following a disturbance. Species resiliency then enables
toleration of such changes in ecosystem conditions and promotes adaptations (Bottom et
al., 2009). The adaptation of salmon habitat occurs across multiple scales, including shifts
in climatic, economic, and geopolitical regimes.
In contrast, salmon adaptations on a species level, such as response diversity,
occur on social, behavioral, or genetic levels (Bottom et al., 2009). Social adaptations in
salmon may include the mating process, instinctually seeking genes within populations
diverse from their own (Bottom et al., 2009). Behavioral adaptations in salmon could
include homing and spawning behavior, which could be altered based on stress, such as
changing stream temperatures, increased predation, lack of proper habitat, etc. (Schreck
et al, 1997). Genetic adaptations in salmon consist of natural control responses, subject to
continual modifications, which adjust the structure and abundance of their populations
(Milner et al., 2003). Response diversity measures phenotypic plasticity – the ability of

20

salmon species of one genotype to produce offspring with another genotype under
changing environmental conditions (Waples et al., 2009). For example, the growth rate
of salmon will vary between individuals depending on water temperature. In their 2009
paper, Bottom, Jones, Simenstad, and Smith explained the importance of response
diversity of salmon in responding to warmer oceans or less productive ocean currents.
They found that during periods of extreme climatic fluctuations, the growth rate and
development of individuals became staggered within a particular population.
Morphological heterogeneity of a population allows for differences in nutritional
requirements, prey availability, position in the water column, and timing of migration. In
this way, a population was able to occupy different levels of the trophic web and exploit
separate resources. The researchers proposed that the evidence of response diversity
occurs as a means of distributing the hardship of sudden environmental change across a
population. Response diversity means that not all individuals occupy the same niches at
any given point in time. Thus, it may be considered “an evolutionary strategy for
spreading risk and avoiding brood failure in the presence of unpredictable watershed or
ocean conditions” (Bottom et al., 2009, “Response diversity”).
Iverson (2008) uses the North of Falcon (NOF) monitoring process and looks at
the Genetic Stock Identification (GSI) in the Genetic Analysis of Pacific Salmonids
(GAPS) database using a Fishery Regulation Assessment Model (FRAM). While GSI
data provides helpful insight in researching and understanding the temporal and spatial
scale of salmon genetics/populations, the data has limitations. Kennedy (2008) studied
the abundance of hatchery vs. non-hatchery chinook and found that hatchery salmon

21

numbers far outweighed non-hatchery fish, which suggest that improving habitat may not
be the only factor in trying to increase native fish populations.
In 1990, Waples and Teel discussed the rapid genetic change that occurs in
hatchery salmon populations. They warned that “[a]ccelerated [genetic] change may
compromise the long-term fitness of the species by reducing overall levels of variability
and eliminating adaptive gene complexes…” (Waples & Teel, 1990, p. 145). Therefore,
many of the genetic variations that occurred in hatchery populations might have been
partially in response to artificially engineered conditions, which can often be less extreme
when compared to wild environments. Thus, higher diversity of life histories translates to
an increase in resilience of salmon populations (Waples et al., 2009). The Columbia
River Basin has seen drastic decline in Pacific salmon populations, partly attributed to the
overall reduction of life history diversity among the species (Gustafson et al., 2007).
Compounded by the cumulative effects of dams, hatchery production, intensive harvest,
and habitat degradation, reduced response diversity in the Columbia River populations
may limit salmon resilience to future environmental changes (Bottom et al., 2009).
Lagasse et al. (2014) conducted a study of salmon habitat using a communitybased assessment program which they hoped would successfully inform watershed
management practices by integrating local and scientific knowledge. The program
enabled the collaboration between the Coastal First Nations Regional Monitoring System
(RMS) and the Canadian Provincial government. According to Lagasse et al., the RMS
stream assessment program encouraged the development of crucial related data. The
authors argue that the acquisition of such knowledge is necessary for learning about
salmon conservation from the perspective of the First Nations community and thereby

22

enhance restoration efforts by integrating local knowledge with western science. While
Lagasse et al. focused on the Great Bear Rainforest in Canada, it may be possible to
implement their study protocols in other salmon habitats; however, their study lacks any
information regarding native versus non-native vegetation. This thesis seeks to cover that
common information gap.
Larsen et al. (2004) examined trends in both spatial and temporal habitat changes
over time, surveying 392 stream reaches for a duration between one and six years each.
They agree with Lagasse et al. and added that to adequately gauge habitat changes,
“research could focus on specific geographic subpopulations of streams [and] specific
stream channel types within them[; additionally,]… it seems wise to begin monitoring
programs that focus, at a minimum, on a core set of habitat elements, recognizing that
complete agreement on the exact set, and the field procedures for their measurement, is
unlikely” (Larsen et al., 2004, p. 289). Malick et al. (2017) attempted to take this one step
further, examining a few specific challenges to ecosystem-based management (EBM)
policies. The researchers found that the ability to make EBM policies for salmon species
was largely affected by lingering scientific uncertainties about human impact and
consequences, ecological processes occurring in too small or large an area to be widely
applicable, spatial asymmetries in the distribution of costs and benefits associated with
management decisions, and static management strategies that prevent timely action based
on current science. Ultimately, since salmon migrate, management of habitats should
account for their entire range. Furthermore, the impact human activities have on the
ecosystem services provided by salmon should be considered. Equivalent management
resources should be made available based at this scale level (Malick et al., 2017).

23

2.2 Invasive Vegetation Introduction
There remains some ambiguity surrounding the validity of invasive vegetation
management. Mark Sagoff (2005) and Rejmánek et al. (2002) discussed the difficulty of
defining terminology surrounding words and concepts related to ecology, such as
‘invasive/invasion’, ‘naturalized’, ‘native’, and ‘exotic’. Thus, more efficient
management occurs when the various agencies share the same understanding of these
definitions, allowing for deeper communication. Noxious weed research has advanced to
the point at which it can now unequivocally quantify many environmental driving factors
that contribute to a particular plant’s tendency to become invasive. These factors include:
a greater phenotypic and genotypic plasticity (Walls, 2010), production of defensive
compounds (allelopathy) (Inderjit, 2005), interspecific associations (i.e., mycorrhizal
relationships) (Henderson et al., 2006), rapid evolutionary changes, and climate change
(Sun et al., 2020).
One influential factor that promotes invasibility includes the plant species’
potential to propagate beyond a stable population. IVS dominate new territory based on
traits which allow them to capitalize in ways the native species cannot. This can result in
their population growing exponentially (Henderson et al., 2006). Allendorf and Lundquist
(2003) discussed how invasive species go against the foundation of what we know about
genetics in small populations. Initially brought over in isolated small populations, these
invasive species can overcome the problems of inbreeding, reduced genetic variety, and
the bottleneck effect; in addition to outcompeting already established native counterparts.
Allendorf and Lundquist (2003) explain some of these anomalies, such as how a lack of
predators could allow the IVS to divert energy it would have used in defending itself to

24

energy used for creating more offspring. This energy surplus could translate to a greater
success towards outcompeting the natives (Allendorf and Lundquist, 2003). However,
more research needs to be conducted before fully understanding the phenomenon behind
the concepts that allow IVS to overcome such obstacles and become aggressive
competitors.
This section helps to illustrate the commonalities of IVS, but does not
comprehensively explain their characteristics, traits, and behaviors. The subject of
invasive species science continues to be nuanced in high complexity and interspecific
relationships which have only recently been explored. Nonetheless, the need for noxious
weed mitigation on behalf of Pacific salmon habitat restoration has a foundation in strong
scientific research and supportive evidence.

2.2.1 A Growing Problem
Only recently have we begun to fully acknowledge that humans play a major part
in the distribution, spread, and management of invasive plants. Similarly, the impacts of
such species to various ecosystems have been a more recent topic of study (Ewel et al.,
1999; Henderson et al., 2006). Henderson et al. (2006) also goes further into theoretical
explanations for invasion success by plants. For instance, a greater genotypic/phenotypic
plasticity of a species may allow it to adapt more readily to a novel environment
(Henderson et al. 2006). The mechanisms which promote invasiveness in non-native
plant species can vary greatly between situations and circumstances. Several current
hypotheses attempt to explain the possible processes which may enable invasion by a
species. Often labeled by catchy names, such as ‘biotic resistance’, ‘resource fluctuation’,
‘superior competitor’, ‘enemy release’, and ‘invasion meltdown’, these concepts provide
25

theoretical frameworks which describe how certain plant species may achieve success
and abundance in a novel ecosystem (Inderjit, 2004). This thesis will not go in-depth to
the characteristics that promote invasion, instead it will elucidate the harmful effects that
currently established IVS have on Pacific salmon habitat.
The presence of invasive vegetative species constitutes a growing concern for the
health of ecosystems (Delach, 2006; Simberloff, 2003; Stuart, 2015) in Washington State
(Smith, 2018). The current management strategy regarding IVS thus far has been
inadequate, and the problem continues to progress. In a 2005 article in the Ecological
Society of America, Simberloff, Parker, and Windle described this failure as a resulting
combination from insufficient policies and research, partially due to a lack of appropriate
funding as well as gaps in the scientific knowledge. These shortcomings only exacerbate
the rapid spread of IVS in Washington State (Simberloff et al., 2005). Although
Washington has taken a proactive stance on IVS management, the problem persists. A
brief explanation of the state’s IVS prioritization will be necessary to describe the current
circumstances and severity of the issue. IVS have been categorized into three
designations based on their current distribution status. These classifications range from
Class A to Class C. Class A has the smallest population sizes and Washington mandates
control for each of these species, while Class C includes recommended control due to
having such a large population that control becomes too costly or timely, and Class B lies
between them in prevalence and priority of control. These classifications are further
explained in Chapter 2.3.3.

26

2.2.2 Anthropogenic Impacts
Numerous causes of IVS proliferation exist, but the most significant among those
includes human activities. In fact, homo sapiens owe much of their success to the
deliberate redistribution of plant species (Henderson et al., 2006). This began with the
advent of agriculture, in which humans selectively cultivated certain beneficial plants and
subsequently translocated those species outside of their geographical barriers (Henderson
et al., 2006). As a common side effect of human activity and development, “invasive
species can cause dramatic changes to ecosystems, including shifts in species
composition, species mortality, biodiversity, disturbance regimes, and ecosystem-level
nutrient dynamics” (Reo et al., 2017, p. 201).
Human-caused introductions of invasive species occurs by a wide array of
mechanisms including agricultural practices, forestry, inadvertent dispersal of seeds or
propagules, importation of contaminated foreign products, and deliberate cultivation.
Typically, anthropochory of invasive vegetation most often occurs unintentionally. Some
species easily adhere to clothing, pets, or car tires and are transported in that manner. IVS
can also escape from nearby gardens or can be deposited as yard waste in natural areas.
Furthermore, modern advances in efficient transportation technologies and development
of intercontinental shipping logistics only exacerbates the spread of invasive plants by
increasing their rate of distribution (Smith, 2018).

2.2.3 Benefits of IVS
Invasive vegetation can provide benefits as well as the widely understood
negative impacts. As mentioned previously, the first attempts at translocation of
vegetative species occurred for the benefit of human livelihood and society (Sagoff,
27

2005). Humans have depended on non-indigenous plant species throughout much of their
history. The reason for this dependence ranges from “…food, shelter, medicine,
ecosystem services, aesthetic enjoyment, and cultural identity” (Ewel et al., 1999, p.
619). Quantifying the impact of a particular vegetative species in terms of a cost-benefit
analysis can be complicated. This complication becomes evident in the many documented
cases of an IVS being deliberately propagated; often, such a species will be provided to
consumers as a beneficial organism (Coelho, 2018; Chace, 2013). For example, the most
notorious noxious weeds within North America includes Himalayan blackberry (Hays,
2012). Yet, this species of blackberry remains revered for its many benefits. Humans
commonly harvest the large nutritious fruit, while inadvertently spreading its seeds across
landscapes (Soll, 2004). Additionally, many people use the thorny thicket of Himalayan
blackberry to act as a ‘barrier’, this same concept forms in the wild, where the barrier
prevents the movement of wildlife, especially fauna such as deer (Soll, 2004).
Beekeepers appreciate the benefits of Himalayan blackberry and another highly invasive
species, purple loosestrife (Lythrum salicaria), due to the belief that it improves the
palatability of honey (Chace, 2013, p. 13).
Another reason for fondness of IVS includes aesthetic value. Several species of
ornamental plants cause severe impacts to the ecosystem, economy, and human health
(Aronson et al., 2016; Pejchar & Mooney, 2009; Simberloff, 1996). English ivy (Hedera
helix) and Morning Glory (Convolvulus arvensis) have long been admired for their
beauty. Often seen adorning the sides of old buildings or growing over garden trellises,
these plants can efficiently overcrowd and smother native species (Western Washington
University, 2019). English ivy has been known to grow to a height of ninety feet as a vine

28

(Chace, 2013, p. 218). Yellow archangel (Lamiastrum galeobdolon) commonly escapes
gardens and forms dense root-mats while outcompeting the native vegetation and
displacing wildlife food as well as habitat. Additionally, the moment of initial
observation of an invasive vegetative species happens long after the species has had time
to establish itself, thus leaving management always ‘a step behind’; which can vary
depending on each species’ or locale’s circumstances (Ewel et al., 1999).
In his book, Invasive Plant Medicine, Timothy Lee Scott describes the numerous
ways in which various invasive plant species can be utilized in homeopathic and clinical
medicines (Scott, 2010). For instance, Japanese knotweed (Fallopia japonica) can be
used to treat Lyme disease, West Nile disease, the flu, Staphylococcus aureus,
Streptococcus pneumonia, E. coli, and Salmonella (Scott, 2010, pp.142-149). Also, both
English ivy and the tree of heaven (Ailanthus altissima) have been used to treat malaria
as well as dysentery (Scott, 2010, pp.142-149). The tree of heaven has further been used
to also treat giardia (Scott, 2010, p. 147). Although there have been many benefits
derived from invasive vegetation, by definition, the harm caused by IVS outweighs any
potential benefit.

2.2.4 Disadvantages of IVS
To address any ambiguity concerning the classification of IVS, the essential
nature and characteristics of IVS must be examined more thoroughly. Invasive vegetation
includes those plants whose current traits and behaviors have been widely regarded as
more harmful than beneficial (RCW 77.135, 2017). Often, when left unchecked, these
plants can multiply at exponential rates (USFS, 2004). Many IVS reproduce so
vigorously that they form a monoculture in the area of proliferation (Poland et al., 2021;
29

Polster et al., 2006). By doing so, that species could reduce local biodiversity to
negligible amounts. When monoculture proliferation of IVS occurs, the native ecosystem
can suffer catastrophic results (Ainouche, & Gray, 2016; Byun et al., 2018; Godfree et
al., 2017; USFS, 2004). In extreme cases, the entire trophic web collapses. Without
substantial mitigation efforts, desertification becomes a possible outcome. Ravi et al.
wrote a paper, titled Can Biological Invasion Induce Desertification, and explored the
function of invasive exotic grass species in extreme desertification events (2009). They
concluded that IVS can contribute to complete sterilization of localized areas by
chemically altering the environment, increasing erosion, providing fuel to wildfires, and
depleting soil nutrients (Ravi et al., 2009). Instances of IVS concentrations rarely reach
this level of severity, which could be mostly attributed to the many
agencies/organizations/etc. which have taken a serious interest in IVS management
practices.
Observing secondary effects of IVS on freshwater environments, such as impacts
to invertebrate populations (Going & Dudley, 2008), alterations to water chemistry
(Hladyz et al., 2011), changes to stream structure, and decrease in DO (Kuehne et al.,
2016) can be apparent. A 2020 thesis by Angela Dillon demonstrated the dysfunction of
IVS on salmon habitat by statistically correlating the presence of invasive plants to the
reduction of macroinvertebrate populations within the Puyallup-White watershed in
Western Washington. In her study, Dillon compared taxa concentration of salmon habitat
restoration sites managed for IVS with unrestored areas. She found that after three years,
higher biodiversity existed within restored sites when compared to unrestored areas
(Dillon, 2020).

30

In this ecologically dynamic world, it has become increasingly apparent that
humans must intervene in the diminishing function of natural systems to preserve Pacific
salmon habitat (Bottom et al., 2009); especially, when humans and numerous other
species greatly benefit from healthy salmon populations (Garibaldi & Turner, 2004;
Helfield & Naiman, 2006; Hyatt & Godbout, 2000). IVS undoubtably play a role in the
decline of salmon numbers, and the content within this thesis will attempt to clearly
illustrate the extent of that role.

2.2.5 Economic Impact of IVS
Invasive species have a national impact cost measured in billions of U.S. dollars
annually (Jardine & Sanchirico, 2018; Reo et al., 2017; USFWS, 2012); a portion of that
total goes towards IVS management. The cost of noxious weed control to business,
commerce, and citizens in Washington State continues to be of great interest in recent
years. Furthermore, the costs of managing individual species only increases over time as
its presence becomes more established (Figure 5). This increasing management cost
shows how important prevention can be when managing for invasive species.
A coalition of environmental agencies, including the Washington State Noxious
Weed Control Board (NWCB), the Washington Invasive Species Council (WISC), and
the Washington State Department of Agriculture (WSDA), contracted the firm
Community Attributes Inc. (CAI) to run an analytical model predicting the potential
impact cost of 23 selected high-priority invasive species to Washington State (2017).
This high-priority species list includes plants, animals, and invertebrates.

31

Figure 5: The invasion curve
The invasion curve demonstrates how management costs increase over time as the area becomes more infested by an invasive species
(Adapted from the Victorian Department of Primary Industries, 2010).

In 2018, the Washington Noxious Weed Control Board published the results of
that analysis and found that those 23 species, if left unchecked, could cost the state
upwards of $1.3 billion in economic losses to agriculture, infrastructure, navigable
waterways, property value, recreational activities, etc., each year (Washington Noxious
Weed Control Board [NWCB], 2018). This analysis excludes estimates from the dozens
of additional economically detrimental ‘mid-priority’ invasive species. Yet, when
comparing the potential cost of a ‘do nothing’ approach to that of the current Washington
State budget for IVS management, the mitigation efforts become the fiscally responsible
option.
Washington State maintains a flourishing recreation industry which supports
248,000 jobs and contributes over $40 billion yearly in total economic contributions,
according to a 2020 report by the Recreation and Conservation Office (RCO). This same
32

report indicates that ecosystem services provided by Washington state recreational lands,
such as “climate stability, disaster risk reduction, soil retention, … water supply, and
carbon sequestration” ranges between $216 billion to $264 billion in yearly value (RCO
report, 2020). Therefore, the threat from IVS demonstrates a clear and present danger to
Washington State’s economy and environment.
The biennial amount of support from the Washington State general fund for the
Noxious Weed Program in 2017 was $864,367 (NWCB, 2018). According to Washington
State Citizen's Guide to the Budget – 2019 (Staff of the Senate Ways and Means
Committee & Legislative Evaluation and Accountability Program (LEAP) Committee
[SWM & LEAP], 2019), Natural Resources departments gets a combined total of about
2% of the biennium budget for 2017-19; this includes the Department of Ecology, Fish &
Wildlife, State Parks and Recreation, etc. Other state agencies and universities spend
more than $25 million a biennium to control invasive species in Washington
(2Washington Invasive Species Council [WISC], 2016).
Washington State has a thriving forestry industry deeply invested in Invasive
plant management (NWCB, 2018). The 2017 CAI report estimates the economic loss
from the twenty-three high priority species for the Washington timber industry to be
approximately $124.8 million annually. Scotch broom (C. scoparius), a ubiquitous class
C noxious weed in Washington State, has a marked effect on conifer suppression (Jetter,
2000); thereby, posing potential negative impacts on growth rates to commercial forests
(Slesak et al., 2016). Daniel Simberloff, a consummate authority on invasive species
science, states that “Several introduced plant species simultaneously affect many native
species by drastically modifying existing fire regimes” (Simberloff, 2013, p.14). This

33

modification can translate to timber resource vulnerability and potential economic loss
during a severe wildfire event.
The agricultural industry, remaining tightly bound to the salmon habitat
restoration debate, has shown a strong negative correlation between IVS presence and
profitability. The 2017 CAI report indicates that the twenty-three invasive species
analyzed had a total potential economic impact of $239.5 million yearly for
Washington’s agricultural industry. IVS impacts all agricultural sectors, costing millions
of dollars to control, and reducing operational productivity (NWCB, 2018). Attempts to
manage IVS on cropland ecosystems can be costly and very complicated. The cost of
invasive plant management to farmers and agricultural workers eclipses the total
combined cost of insects, rodents, and pathogen management (Mullin et al., 2000).
Livestock ranchers also suffer effects of IVS spread. Approximately three
quarters of all domestic animals depend on rangelands for sustenance (Mullin et al.,
2000); these ecosystems are uniquely susceptible to IVS. Increased instances of drought
can promote non-native species that adapt more readily than native vegetative species to
such arid conditions (Skaggs, 2008). As such, rangeland ecosystems suffer from low
resilience, changing climate conditions, and competition from non-native vegetation
(Skaggs, 2008). The authors of the 2017 CAI report claim that potential economic losses
from the 23 priority invasive species to livestock ranchers in Washington State totals
approximately $120 million each year. Some noxious weeds, such as the various
knapweed species and yellow star-thistle (Centaurea solstitialis), have become a problem
to Washington ranchers in recent years because of their unpalatability to livestock and
tendency to outcompete forage species that herds depend on (NWCB, 2018). Many other

34

IVS, such as poison and water hemlock (Conium maculatum & Cicuta douglasii), kochia
(Bassia scoparia), common groundsel (Senecio vulgaris), tansy ragwort (Senecio
jacobaea), and many others can cause problems in multiple species of livestock ranging
from sickness to death (NWCB, 2017). These examples help to illustrate the
interconnectedness of invasive vegetation and the economics in Washington State. This
thesis will attempt to clearly relate the topics mentioned in this section to the salmon
population crisis and the ways in which humans, salmon, and the economy may mutually
benefit.

2.3 Restoring Salmon Habitat
The benefits of restoring Pacific salmon habitat transcend any economic, cultural,
or environmental reasons. The obligation falls upon humans to do everything possible to
ensure the survival of this species. Indigenous peoples have had a relationship with these
animals much longer than any other culture/ethnic group, and they understand the
urgency to preserve and protect them. While he was serving as the Chairman of the
Northwest Indian Fisheries Commission, Billy Frank jr. expressed this responsibility as
follows, “It is our inherent duty to protect them, and to the degree that we fail to do so,
we fail as human beings” (Frank & Neumeyer, 2015, p. 26).

2.3.1 Habitat Requirements
Put into the simplest terms possible, the habitat of Pacific salmon includes the
Pacific Ocean and its constituent streams, rivers, lakes, and inlets. The native range of
Pacific salmon spans from Northern Mexico to the Arctic Ocean on the North American
continent and from Southern Japan and Korea to the Arctic Ocean on the Asian continent
(Quinn, 2005). These anadromous fish can regularly travel hundreds of kilometers inland
35

during homing migrations (Quinn, 2005, pp. 37-52). For the purposes of this thesis,
oceanic populations of salmon species will largely be omitted from discussion. Further
examination of the freshwater system will be necessary to fully grasp the environmental
conditions which support healthy salmon populations. Glacial meltwater from the high
elevation ranges of the Cascade and Olympic mountains feed the rivers, streams, and
lakes of Washington. These spring glacial melts provide salmon with enough clean cool
water to navigate their way upstream to spawning sites (Close, 2015). Furthermore, the
glacial till and lithology of these streams provide proper gravel substrate for egg
deposition and embryonic development (Quinn, 2005).
Climatic fluctuations have caused instability in natural systems, which adds to the
difficulty of predicting future conditions of Pacific salmon habitat. For example, the
general atmospheric warming trend observed in recent years has caused earlier snowmelt
which altered seasonal flow regimes in many Washington rivers (Zhang et al., 2019).
Evidence of this change can be observed in Washington’s Columbia River Basin, a major
salmon migration route. A 2009 study of the effects of climate change on freshwater
salmon habitat in Washington State provided strong evidence that the prolonged duration
of low summertime flow is problematic for many salmon populations that migrate,
spawn, or rear in the interior Columbia River Basin (Mantua et al., 2009). Though the
primary focus of this thesis does not include climate variability, future research would
benefit greatly from linking IVS and salmon habitat to climate change.
Aquatic environments must contain adequate concentrations of DO in order to
support populations of salmonid species. DO regulates metabolic activity and permits
strenuous exertion during migration, making it essential to salmon health and survival

36

(Fellman et al., 2015). Thus, oxygen depleted environments pose lethal risks to salmon.
Low DO levels deprive salmon of oxygen required to breathe, feed, or swim upstream to
spawn. Even if adults can migrate upstream, anoxic levels deprive salmon eggs, fry, and
juveniles of the oxygen required for their growth and development. This can seriously
affect the vitality of future generations.
The oxygen requirements for salmonids vary according to several factors
including, season, life stage, stream temperature, metabolic activity level, time of day,
and species. A study conducted in 1989, using respirometric analysis and a simulated
natural light cycle, indicated that rainbow trout oxygen intake fluctuated between 100 and
360 milligrams of O2 per kilogram of fish weight per hour during an eighteen-hour
period. The highest levels of oxygen consumption by the fish were recorded during the
greatest intensity of light exposure, while the lowest respiration occurred in darkness
(Steffensen, 1989). Most diurnal ectothermic fish species, including salmon, commonly
adhere to circadian respiratory cycles (Eliason & Farrell, 2016). Furthermore, the
respiratory rate of salmon varies relative to their digestive activity; oxygen requirements
are higher during active food consumption and lower during periods of homing starvation
(Van Leeuwen et al., 2012). Not only does DO concentration directly affect the faunal
species that inhabit an aquatic ecosystem, but it also enables populations of invertebrates,
plants, and microbes, thereby influencing the composition of the entire local biome (Doke
et al., 1995).
Varying levels of DO concentration can have either a positive or negative
correlation to organism abundance depending on the species involved. For instance,
anaerobic microbial colonies can thrive in low DO environments, further altering the

37

chemistry of the local ecosystem by their metabolic processes. Many of these organisms
can be extremely harmful to the health of fish and humans alike. For example, the
notorious anaerobic bacteria Clostridium botulinum type E causes considerable mortality
in juvenile salmon reared in earth bottom ponds (Abdelsalam, 2017).
Conversely, aquatic macroinvertebrates with tracheal gills or submergent
respiratory mechanisms depend on DO much the same way that fish do, and there exists a
positive relationship between species abundance and DO levels (Jacob et al., 1984).
Much of a juvenile Pacific salmon’s diet consists of such macroinvertebrates which spend
all or some of their life stages in the aquatic ecosystem. The larval stage of some salmon
prey species, such as mayflies (Ephemeroptera), caddisflies (Trichoptera), and stoneflies
(Plecoptera), possess gill adaptations which require constant oxygenation in order to
survive (Dillon, 2020).
Water temperature has a direct control on DO levels; see Table 3. Thermally
stratified bodies of water have marked variations of oxygenated water layers due to this
temperature control function. In 2002, researchers for the University of Thessaloniki,
Greece proposed a model to simulate oxygen distribution in stratified lakes, in which the
thermocline prevents oxygen transfer between the epilimnion and hypolimnion. The
researchers determined that in these situations, oxygen sources are restricted primarily to
the epilimnion (Antonopolous & Gianniou, 2003). Examination and analysis of aquatic
biology in lentic ecosystems revealed that primary respiration of the organisms that
resided in the hypolimnion, as well as seasonal deposition of reduced material, accounted
for the depletion of DO in that water layer (Antonopolous & Gianniou, 2003). These
findings have relevant implications for lacustrine habitats of salmon in Western

38

Washington due to salmonid’s biological sensitivity to temperature and aqueous DO
concentrations.
Table 3: Physical Parameters of Lotic Waters
This table illustrates various environmental factors associated with dissolved oxygen in riverine ecosystems (Adapted from Fellman et
al., 2015, Table 1).

Lotic environments also have a direct temperature-oxygen relationship, similar to
lacustrine environments, in addition to several factors of DO control unique to riverine
ecosystems (see Table 3). These factors include flow regime, turbidity, sedimentary
inputs and bank erosion, salmon spawning processes, as well as decomposition of salmon
carcasses (Fellman et al., 2019) An in-depth examination of the various ways in which
the top IVS alter the environmental factors that affect water flow, turbidity, and
allochthonous inputs will be covered throughout Chapter 4.
Habitat temperature variations outside optimal ranges can create complications in
salmon species (Zhang et al., 2019). Pacific salmon require cool water temperatures
around 13°C (~ 55°F) for optimal healthy function (Zhang et al., 2019), but not in excess
of around 23°C (~ 73°F) (Mantua et al., 2009). Fellman et al. conducted a field study
which analyzed the stream conditions in two Alaskan watersheds over the course of a sixmonth period, and determined that DO concentration peaked around May, when water
temperature was between approximately 2 - 4°C (~ 36 - 39°F) (2015). Temperature
39

affects many water quality parameters, including nutrient cycling, biological productivity
(Antonopolous & Gianniou, 2003), metabolic activity of salmon, and the solubility of
dissolved gasses, such as carbon dioxide and oxygen (Fellman et al., 2015). The
Washington Department of Ecology (Ecology), with approval from the Environmental
Protection Agency (EPA), established water temperature standards for Pacific salmon
habitat in Chapter 173-201A of the Washington Administrative Code (WAC, 2020).
Therein, contains a water temperature range going from healthy function to life
threatening. Such temperature ranges include a healthy temperature at less than 14°C (⁓
57°F), while temperatures above 14 °C increases disease and stress, and temperatures
over 23°C (⁓ 73°F) can be lethal (Mantua et al., 2009). Regular temperature readings
conducted on the Columbia and Snake Rivers in Washington showed that some sections
of these crucial salmon habitats regularly reached 20 - 23°C (⁓ 68 - 74°F) (Beechie et al.,
2013; Mantua et al., 2009; Zhang et al., 2019).
A necessary component of stream structure in salmon habitat includes DWD
(May et al., 1998; Nelson et al., 2015), as it provides shelter to salmon, creates pools and
side channels, as well as houses macroinvertebrates (Close, 2015). Juvenile salmon are
especially dependent on shelter for many reasons. Not only does the existence of shelter
decrease the risk of predation but it may also provide metabolic benefits to young fish
and thereby improves growth potential and development. For example, a 2006 study
provided measurable evidence that adequate shelter abundance translated to a reduction
in energy budget of juvenile salmon, due primarily to the fact that increased vigilance of
predators equated to greater physiological stress and energy expenditure (Millidine et al.,
2006). Furthermore, the ability of drift-feeding fish, such as juvenile Pacific salmon, to

40

effectively consume prey items depends on the availability of low-velocity zones created
by DWD (Hafs, et al., 2014). In their 2015 study, Nelson et al. analyzed the ten separate
habitat characteristics that they hypothesized would affect the density of spawning chum
and pink salmon. Their research indicated that, out of those ten considerations, the most
significant characteristic correlating to spawning pink salmon densities had been the
presence of large woody debris; for chum, it appeared to be water pH.
Several professional and academic projects in recent decades have provided
insight into the importance of DWD inclusion in salmon habitat. The 2011 Chehalis
Basin Salmon Habitat Restoration Strategy included a comprehensive long-term
management plan in which DWD installation projects remain a high priority. This
strategy illustrated the several ways in which DWD features enable a wide range of
habitat benefits. For instance, juvenile salmon prefer to over-winter in the deep pools
created by DWD (Kliem & Holden, 2011). A 2014 paper, titled Quantifying the role of
woody debris in providing bioenergetically favorable habitat for juvenile salmon, utilized
hydrodynamic and bioenergetic models to simulate the effects of DWD components on
several stream characteristics, including flow, velocity, and turbidity (Hafs et al., 2014).
The models included simulations for six different configurations ranging from sparse
placement to excessive placement of DWD as illustrated in Figure 6. The authors used
linear regression models to predict the favorable juvenile salmon habitat. The findings of
this study showed that in the absence of DWD, there was not adequate juvenile salmon
habitat. Conversely, the models indicated that high abundance of DWD reduced stream
velocity by as much as 5% - 19%, and juvenile salmon habitat area increased by a factor
of four (Hafs et al., 2014).

41

Figure 6: DWD placement simulation
Correlation of Down Woody Debris (DWD) to stream velocity and juvenile salmon growth potential. This simulation shows how
potential salmon growth occurs at a positive correlation to the addition of DWD placement within a reach of stream (Hafs et al.,
2014, Figure 1).

This section summarizes the basic requirements of optimal Pacific salmon habitat
but does not delineate conditions for individual species or populations of fish. The
minimum target range for each of the vital environmental criteria for Pacific salmon
habitat covered in this thesis will be assessed partially on the requirements for the WAC
standards concerning the ‘salmonid spawning, rearing, and migration’ category set by the
EPA (Table 2) (WAC, 2020). The remaining criteria, not addressed within these
standards, will be based on cumulative data gathered from various comprehensive
scientific studies; with the understanding that many of the criteria examined is site
specific and should be reassessed accordingly. The impacts on salmon species habitat
based on these criteria ranges will be further examined in Chapter 4.
2.3.1.1 WAC Standards. The WAC water quality standards have been
designated for fresh surface waters to protect aquatic life, with a focus on salmon species.
42

These WAC standards provide detailed information about temperature, dissolved oxygen
(DO), turbidity, and pH. These standards have been established in accordance with
Washington State Department of Ecology guidelines for water quality and approved by
the EPA.
WAC water temperature criteria has been designed with consideration of Pacific
salmon biological responses, as a way to limit potential harmful effects, such as reduced
feeding or starvation, thermoregulative stresses, and decrease in spawning activity and
reproduction; which can contribute to lower survivability (Sauter et al., 2001). Water
temperature remains an important factor for salmon survival and is directly linked to the
available DO content in a water source. Washington standards for stream temperatures
over a seven-day average of the daily maximum are suggested to not exceed 17.5°C (⁓
63.5°F) (WAC, 2020).
DO is a measure of the amount of aqueous oxygen in the water and is essential for
the respiratory function of aerobic life (Finch & Brown, 2020). Low DO concentrations
can cause negative impacts to growth and development of salmon at all life stages, and
can affect swimming, feeding, and reproductive behaviors of both juveniles and adults
(Carter, 2005). Washington standards for spawning, rearing, and migrating salmon range
between 8.0 to 9.5 milligrams per liter as the minimum range during a 24-hour period
(Finch & Brown, 2020).
Fine sediment generally consists of particles less than 2 millimeters (~ 0.08
inches) and can block water flow and oxygen, increase fish mortality, reduce habitat, and
lessen the success of hatching embryos (Finch & Brown, 2020). One measurement for
suspended fine sediment concentrations includes turbidity, which can be expressed in

43

"nephelometric turbidity units" (NTUs) (WAC, 2020). The higher the NTU number, the
more turbid and murkier the water appears. It is recommended to consult WAC 173201A-200 directly for each case to reference the appropriate use of NTUs. NTU values
are unclear as they have been based on information compiled from a particular stream’s
history, which varies by stream, instead of by salmon requirements. Currently, these
measurements are used in reference to NTU values previously collected for that particular
waterbody, which may not depict a clear long-term profile of local turbidity. However, it
has been suggested by some Washington ecologists that this method of turbidity
assessment be revised in respect to salmon needs (A. Dillon, personal communication,
May 10, 2021; Finch & Brown, 2020).
The pH of a stream needs to remain within 6.5 to 8.5, with an allowance of 0.5
units of deviation for human-caused variables (WAC, 2020). As deviation from these pH
standards increases, the worse the physiological effects can be for the fish inhabiting that
water body, ranging from diminished growth rates to mortality (Robertson-Bryan, Inc.
[RBI], 2004). Severe effects of high pH on fish include “hypertrophy of mucus cells at
the base of the gill filaments and destruction of gill and skin epithelium, with effects on
the eye lens and cornea” (Alabaster & Lloyd, 1980, and Boyd, 1990, as cited in RBI,
2004). Effects of acidic water conditions, or low pH levels, manifest in respiratory
distress and osmotic imbalances in salmon species, which translates to a reduction in
growth rates and survivability (RBI, 2004).

2.3.2 Human Impacts
Freshwater habitat loss and degradation remain among chief factors contributing
to the decline of Pacific salmon populations (Bisson et al., 2009; Hill et al., 2010).
44

Anthropogenic alterations to the environment advance this destruction (Lackey, 2003),
and nearly every aspect of urban development promotes changes to salmon habitat.
Human activities of notable concern include excessive commercial and recreational
fishing, dam building and operation, flood control, municipal or commercial components,
hatchery culture, as well as certain farming and ranching practices (Lackey, 2003).
A primary consideration in the salmon habitat conservation debate includes
mankind’s use of water. In the last hundred years, half of the world’s wetlands have been
drained, 48,000 large scale dam construction projects have been completed, and
approximately 80% of the Earth’s large rivers have been diverted for human purposes
(Vince, 2014, p.72). According to a dam inventory report in September of 2020, the
Washington Department of Ecology regulated 1,226 separate dams in the state
(Washington Department of Ecology [Ecology], 2020). Dam building and operation
fundamentally changes natural salmon habitat in Washington State.
Numerous other methods of water diversion used by humans also cause impacts
to natural systems. Take for instance, the ways in which water has been redirected to
facilitate Washington’s public road construction. The high court determined these
methods to be detrimental to salmon; therefore, remediation has been mandated (Brown
& Footen, 2010, Blumm, 2017; Donovan, 2016). Water use and redirection by humans
may have a profound effect on the distribution and spread of certain IVS species.
Although hydraulic systems are not the focus of this thesis, they must be taken into
consideration as a potential vector for IVS dispersal.
Hydrochory, a process of long-distance passive vegetative propagule dispersal
along a waterway, may increase the spread of invasive species (Nilsson, et al., 2009).

45

Several high priority invasive plants in Washington State, such as Scotch broom, reed
canarygrass (Phalaris arundinacea), and Himalayan blackberry commonly propagate by
hydrochoric means (Woodward et al., 2011). Knotweed species often infest large areas of
riparian zones and reproduce predominately by aquatic transport of rhizome fragments
(Arnold & Toran, 2018). Brazilian elodea (Egeria densa), a class B noxious weed in
Washington State, propagates strictly by clonal fragmentation instead of sexual
reproduction, due to the lack of female individuals existing in the state (King County
Noxious Weed Control Program [KCNWCP], 2014).
Properly maintained riparian buffer zones around streams within developed areas
drastically improve stream quality. These vegetative margins offer several functions for
improving stream quality, increasing biodiversity, and enhancing ecosystem resiliency
(Stutter et al., 2019). Suitable salmon habitat has a narrow range of water quality
standards, and any deviation outside of that range may threaten the health of fish and
increase mortality. Neglecting the necessity of including adequate riparian buffers around
streams allows toxic stormwater runoff, excess sediment, and potential biological
contaminants to easily enter freshwater environments that house populations of salmon
(Mooney & Eisgruber, 2001; Wilhere & Quinn, 2018). Conversely, a densely vegetated
wide riparian zone acts as a natural filter for water flowing through it, thereby limiting
any toxic runoff from entering the stream. In addition to water filtration, riparian buffer
zones with substantial canopy cover regulate stream temperature by blocking solar
radiation from reaching the surface of the water (Mooney & Eisgruber, 2001; Wilhere &
Quinn, 2018).

46

A study conducted by Mcintyre et al. (2018) found increasing evidence that toxic
stormwater runoff caused premature mortality to adult transitional salmon. The study also
points out other non-fatal symptoms of water toxicity on salmon, such as loss of
orientation, surface swimming and gaping, and loss of equilibrium (Mcintyre et al.,
2018). A recent analysis of PNW stream water composition by Tian et al. (2020)
indicated that stormwater runoff in developed areas commonly contained a toxic
compound from car tires and has been directly linked to salmon mortality. A previous
study in 2006 shows the strong correlation between urbanization and aquatic ecosystem
degradation in a region of Western Washington. In their paper, titled The Cumulative
Effects of Urbanization on Small Streams in the Puget Sound Lowlands Ecoregion,
University of Washington researchers showed the impacts of urbanization on Pacific
salmon habitat and the role that riparian buffer zones play in mitigating non-point source
pollution in Washington streams. Furthermore, this study demonstrated the implications
of riparian buffer zones for stream quality and biotic integrity in the Puget Sound
Lowlands region (May et al., 1998); see Figure 7. May et al. (1998) found that riparian
buffers must maintain a general minimum width of 30 meters (⁓ 98 feet), or 100 meters
(⁓ 328 feet) in more sensitive areas, in order to mitigate the effects of urbanization. The
data collected in this study indicated that at least 70% of the corridor’s length must be
maintained as a healthy riparian margin to promote optimal stream conditions (May et al.,
1998). These riparian buffers are just one factor in ecological integrity that is best used
when combined with other natural functions (May et al., 1998).

47

Figure 7: Riparian zone quality at various urbanization levels
Model depicting the relationships between riparian buffer widths, biological integrity, and watershed development (taken from May et
al., 1998, Figure 16)

The agricultural industry strongly supports Washington State’s economy and
society. Recently, there has been increased attention brought to this necessary practice,
and the ways in which farming and ranching activities influence the conditions of the
environment. Although there remains much controversy over which farming practices
pose the most significant harm to salmon habitat (Breslow, 2014), many have been
widely identified as undeniably detrimental. Fertilizer use (Seiter, 2008), pesticide
application (Seiter, 2008), riparian canopy reduction (Chapman & Knudsen, 1980), water
capture and irrigation (Essaid & Caldwell, 2017), nutrient inputs from animal waste
(Seiter, 2008), as well as excessive soil tillage (Fu et al., 2006) have been documented to
be among the most notorious dangers to salmon habitat currently in use by Washington
farmers. For instance, Gerald Whittaker, in a 2005 paper titled Application of SWAT in
the Evaluation of Salmon Habitat Remediation Policy, detailed an analytical model used
by the United States Department of Agriculture (USDA) to assess non-point source water

48

pollutants which contributed to the environmental distress of salmon runs in the Pacific
Northwest (2005). Whittaker pointed out that agricultural practices, which include the
heavy application of fertilizers and pesticides, were directly responsible for habitat
degradation from non-point sources (2005). He goes on to describe the cascading effects
that fertilizer can have on lotic systems,
Nutrient loading is thought to be responsible for ‘increased primary and
secondary production, possible oxygen depletion during extreme algal blooms,
lower survival and productivity, increased eutrophication rate of standing waters,
certain nutrients (e.g., non-ionized ammonia, some metals) possibly toxic to eggs
and juveniles at high concentrations’ (2005, p. 841).
Agricultural activities can have a profound effect on aquatic organisms. Soil
tillage can contribute small particulate matter to streams at unnatural rates, which may
adversely affect aquatic organisms. This fine sediment (<2mm) fills spaces between
larger particles, thus reducing the flow of oxygen to salmon eggs, fry, and other benthic
dwelling organisms (Larsen et al., 2004). Average stream temperature can also be
influenced by local farming activities. If the cleared land of an agricultural site abuts a
fish bearing water body, then an adequate riparian buffer zone must be maintained to
regulate stream temperature sufficiently in order to promote optimal conditions for
salmon habitat. The research conducted by Larsen et al. (2004) found that tree canopies
were essential to the cool conditions required for salmon reproduction and growth.
Many commercial farmers have a profit driven perspective concerning their use of
land. In that sense, a common farming practice has been to dedicate all possible land area
to the goal of maximizing production. A case in Skagit Valley, Washington illustrates
this mentality well. From 1996-2008 the Swinomish Tribe pursued legal action against
the local farmers to include a riparian buffer zone of 50-180ft for salmon habitat recovery
(Breslow, 2014). The case eventually made its way to the Washington Supreme Court. In
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the proceedings, the “Skagit farmers argued that habitat restoration on farmland would
undermine an already dwindling land base to the point that arable acreage would slip
below a "critical mass" necessary to maintain the economic viability of the local
agricultural industry” (Breslow, 2014, p. 739). This paper features numerous instances
which allude to a much-needed reformation of the agricultural industry and its degree of
environmental responsibility (Breslow, 2014). Yet, there remains resistance from
agricultural landowners to meet this challenge, which this thesis expands upon in
Chapter 2.4.1. Anthropogenic changes to the habitat of salmon are extensive and will be
a recurring theme throughout this thesis.

2.3.3 Ownership Boundaries
Like all U.S. territories, Washington has been divided into
legislative/congressional districts and counties, and further sub-divided into
municipalities. Each of these distinct areas have designated governing bodies and legal
jurisdictions. These jurisdictions determine allocation of federal and state funding and
legislative function. Municipalities include cities and towns, which have been separated
into public and private land parcels. Often there exists discrepancies between federal and
state laws, much like the differences between county ordinances. This convolution often
causes much discourse regarding environmental law.
Regulatory standards have become a ‘hotbed issue’ for interjurisdictional cases
involving salmon habitat recovery (Bisson et al., 2009; Breslow, 2014; Donovan, 2016).
Difficulties often arise between stakeholders of differing perspectives, conflicting goals,
or interpretations of information regarding policy and regulations. This can be especially
true where an unclear jurisdictional boundary exists. Some of the cases in this thesis will
50

feature such instances, and offer areas of ‘common ground’, in which conflicting
stakeholders may mutually reach amenable solutions to their individual challenges.
The Washington State Noxious Weed Control Board updates the Washington
State Noxious Weed List annually. This includes adding any new species [as well
as] re-classifying any existing species. Noxious weeds are defined in RCW 17.10
as non-native highly invasive plant species. The weed list is divided into three
classifications, A, B, and C. Class A noxious weeds are very limited in
distribution and eradication is required for infestations. Class B noxious weeds are
limited in some parts of the state and more prevalent in other parts. Class B
noxious weeds can be designated by the state noxious weed board for required
control within a county or selected by the county for required control. Class C
noxious weed species are found throughout the state. County noxious weed
boards may select class C species for required control within their county. RCW
17.10 and 17.04 are the [legislative] statutes that require noxious weed control
throughout the state. RCW 17.10 requires that the noxious weed list be updated
annually by the State Noxious Weed Control Board and gives the authority to the
county noxious weed boards to require control of noxious weeds. It also mandates
that [property] owners have the duty to control noxious weed species [on their
lands]. RCW 17.04 is a very similar law governing noxious weed districts rather
than noxious weed boards. Both noxious weed boards and districts have the
authority to enforce noxious weed control on all private, county, and state
landowners within their jurisdiction. Only federal lands are exempt from noxious
weed districts and boards jurisdiction. However, cooperative weed management is
strongly encouraged between state, federal, and local agencies [as well as] private
landowners (M. Fee, personal communication, April 15, 2019).

2.3.4 Habitat Availability
Current predictions claim that salmon habitat loss will be 5% to 22% in
Washington State, by the year 2090 (Mantua et al., 2009). This loss of habitat will be
precipitated mainly by increasing water temperatures and disappearance of glacial ice due
to anthropogenic climate change (Zhang et al., 2019). In their 2002 Roadmap for Salmon
Habitat Conservation at the Watershed Level, The State of Washington Joint Natural
Resources Cabinet proposed that reduced flow, water quality, streambank erosion and
sediment inputs, riparian degradation, habitat accessibility, as well as channel complexity
pose significant risks to Pacific salmon habitat (Washington Joint Natural Resources
51

Cabinet [WJNRC], 2002). Furthermore, future atmospheric warming may render much of
Western Washington’s freshwater environments uninhabitable to Pacific salmon (Zhang
et al.,2019; Rubenstein et al., 2019; Sullivan et al., 2000).
A paper published in 2013 by Beechie et al., used a two-step modelling analysis
to predict future conditions in the Pacific Northwest in regard to salmon habitat
suitability. By using the variation in global climate (VIC) model, which incorporated
dynamic runoff routing, stream flow, and stream temperature simulations, they predicted
that minimum monthly summertime flow rate in the region will decrease by 10% to 70%
by the year 2100. They forecasted a stream temperature increase between 1 to 4°C (⁓ 34 39°F) during the period of 2030 to 2069, and an increase between 2 to 6°C (⁓ 36 - 43°F)
by the year 2100 (Beechie et al., 2013). The findings of this study indicate that future
stream conditions may be incapable of supporting Pacific salmon populations.
Many high priority critical salmon habitats fall within regions which are
especially susceptible to erosional risks. The Columbia River Basin has experienced
drastic changes in hydrologic function since the late nineteenth century. These changes
frequently manifest in ways that have led to the degradation of Pacific salmon habitat.
For example, the 2013 ESA Recovery Plan for Lower Columbia River Coho Salmon,
Lower Columbia River Chinook Salmon, Columbia River Chum Salmon, and Lower
Columbia River Steelhead, cited evidence that sediment deposition from the interior
Columbia Basin to the Columbia River estuary has been reduced to around 40% of the
late nineteenth century volumes (National Marine Fisheries Service [NMFS], 2013).This
has occurred not because of a decrease in bank erosion throughout the Columbia River
watersheds, but as a result of reduced flow throughout the system. This reduction in

52

discharge due to agricultural water usage and municipal hydraulic systems in the region
allows for sediment particles to fall out of solution sooner than they would if flow rates
were higher. This limitation of estuarine deposition has translated to an approximate 60%
increase in sediment loads to the interior Columbia watershed, which includes WRIAs 24
through 29 (Brannon et al., 2004).
The Chehalis Basin Salmon Recovery Plan indicates that riparian degradation,
water temperature increase, low discharge, low DO concentrations, poor water quality,
and bank erosion pose a substantial threat to salmon habitat within WRIAs 22 and 23
(Kliem & Holden, 2011). The main stem of the Chehalis River, a critical Salmon habitat
in Southwestern Washington, experiences high sediment loading from several of its
tributaries including, Satsop River, Wynoochee River, Newaukum, South Fork Chehalis
River, and the mainstem above the town of Doty, WA. (Kliem & Holden, 2011). Lack of
riparian vegetation, inadequate quantities of woody debris, agricultural practices, and
urbanization have contributed to the salmon habitat destruction observed in the Chehalis
River Basin (Kliem & Holden, 2011).
These examples highlight some of the current and future problems facing Pacific
salmon populations in Western Washington and demonstrate a crucial need for habitat
restoration as a means to preserve the species. The conditions detailed above are
commonplace throughout freshwater ecosystems in developed areas of Western
Washington, and salmon habitat availability continues to decline. The following section
will illustrate some of the detrimental effects that IVS have been documented to cause on
Pacific salmon habitat and the related ecological harms to the environment.

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2.3.5 IVS Potential
This section will synthesize concepts taken from previous research and scientific
studies by incorporating those findings into a framework that forms connections between
salmon habitat degradation and IVS proliferation in Western Washington. There have
been rigorous studies conducted on some invasive plant species and their ecological
effects on natural systems, but there currently exists substantial knowledge gaps
regarding the ways in which IVS impact Pacific salmon habitat. Noxious weeds that
cause direct alterations to overall biodiversity, sediment loads, stream chemistry, water
flow regimes, stream temperatures, shelter abundance, migration route obstruction, and
predator habitat should be species of concern for Pacific salmon habitat conservation.
A common error in attempting to quantifying the detrimental effects that IVS
have on local ecology often occurs when comparing a single invasive plant species to its
native counterpart. Two separate vegetative species which may fill the same particular
ecological niche typically provide similar ecosystem services, regardless of their
respective nativity (Sagoff, 2005). The complete truth may only be revealed by
conducting a long-term critical study of the effects that the non-native species has on the
whole ecosystem.
It may also be tempting to assume that a positive correlation between a non-native
species and ecosystem health equates to a low impact assessment of said plant, but this
would be an incomplete analysis. For instance, although the class C noxious weed reed
canarygrass has shown promise as a suitable bank stabilizer in erosion prone areas
(Martinez, 2013), this single metric is insufficient to deem it as ecologically beneficial in
all circumstances. Reed canarygrass has also been documented to reduce the growth

54

potential of juvenile salmon by altering the diversity of macroinvertebrate populations
and limiting accessible lateral stream area (Klopfensein, 2016). Similarly, knotweed has
been shown as an adequate food source substitute of native leaf litter for many aquatic
detritivorous invertebrates (Braatne, et al., 2007), which salmon regularly prey upon, but
it is also notorious regarding stream bank erosion (Arnold & Toran, 2018). These
examples simply highlight some of the pitfalls which may occur in the risk assessment of
IVS regarding Pacific salmon habitat. Many other IVS in Western Washington may
provide some ecosystem services that are equivalent to, or even superior to, their native
counterparts. Therefore, it is imperative to analyze the overall effects of the species to a
comprehensive list of environmental response metrics in order to quantify its inherent
impact level.
The biological or environmental conditions which enable a particular vegetative
species to become invasive may not always be recognized during its early introduction to
a novel ecosystem. Sometimes, the mechanisms of invasion are only understood after
years of prolonged study. Take knotweed for example, recent genetic analysis indicates
that species within this genus propagate primarily through clonal replication rather than
sexual reproduction; previously, science was unable to explain its rapid mode of dispersal
(Engler et al., 2011). Japanese knotweed, often seen growing along the banks of salmon
bearing streams, has become widespread in all but one county within WA (NWCB,
2018). Molecular analysis of this knotweed revealed that only a single male-sterile clone
of the plant introduced into the environment generated its subsequent invasion
(Rotherham & Lambert, 2012). These examples show how long-term observation may be
the best way to determine the true impact of IVS in Western WA.

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Modern science has yet to adopt a unified system for classification and
prioritization of IVS. As a result, invasion ecology features a wide spectrum of opinion
and bias concerning the environmental harm of invasives. The impacts from most
invasive plant species have not been fully quantified, and those that have, are frequently
analyzed by such a limited set of response metrics that their ecological impact may be
considered inconclusive (Barney et al., 2013). This inadequacy can be especially
problematic concerning newly introduced non-native plant species in which risks to the
environment, economy, or public health may not be obvious.
In contrast, other instances of IVS include impacts to the health of humans and
livestock, which can manifest so severely that they become almost immediately apparent.
Poison Hemlock, for example, can arguably be considered the most well-known invasive
plant in the world and has a substantial presence throughout North America. This plant
can cause illness and death when ingested by animals and humans (NWCB, 2017).
Yellow flag iris (Iris pseudacorus), a class C noxious weed in Washington, contains
dangerous toxins harmful to animals and contact with its resin causes skin irritations in
humans (NWCB, 2018). Giant hogweed (Heracleum mantegazzianum), found in 15
western Washington counties, exudes an extremely caustic sap that causes skin blisters
and sensitivity to ultraviolet radiation, exposure symptoms to this plant can last for years
(NWCB, 2018).
The effects that IVS have on salmon habitat can be difficult to quantify because of
the intrinsic complexity of ecosystems and the extensive interspecific relationships
between organisms. The burgeoning field of invasion biology remained ambiguous until
around turn of the 21st century, when the scientific community recognized that more

56

advanced research would greatly benefit this newly founded branch of ecology
(Simberloff et al., 2005). Bisson et al. summarized this inadequacy in regard to salmon
habitat:
Very little is known of the effects of invasive riparian plants on the water quality
and physical habitat of streams inhabited by Pacific salmon. Moreover, the effects
of exotic riparian plants on the contribution of terrestrial organic materials to
aquatic ecosystems have rarely been studied (2009, Climate change section).
Riparian zones of the Pacific Northwest typically have a composition of
heterogeneous sedimentary soils that have been deposited by the influence of water flow
and associated erosional effects (Mikkelsen & Vesho, 2000). The combination of this
type of soil composition, active geology, and moderate to heavy precipitation makes
erosion a frequent occurrence in Western Washington. Native tree species such as
Douglas-fir (Pseudotsuga menziesii) (Sakals & Sidle, 2004), western redcedar (Thuja
plicata) (Bennett et al., 2002), western hemlock (Tsuga heterophylla) (Bennett et al.,
2002), and big-leaf maple (Acer macrophyllum) (Purewal, 2004) have deep extensive
root systems that provide bank stability along water bodies; thereby, regulating soil
erosion regimes.
A plant’s root system has a profound effect on its ability to stabilize stream banks
in riparian zones. Root cohesion is a measure of a plant’s ability to bind soil mechanically
and hydrologically. Mechanical reinforcement by roots contributes to a higher shear
strength of a sloped soil mass, while hydrological resistance of roots decreases soil pore
water pressure; thereby, reducing sub-surface stress loads. (Mickovski & Gonzalez,
2017). Several root characteristics, such as depth and total underground root volume
(Gyssels, et al., 2005), fiber tensile strength (Roering, et al., 2003), and quantity of fineroot material (Martinez, 2013), contribute to a plant species’ overall root cohesion value.
57

Root strength is often quantified as a function of root diameter, in which fine roots
maintain a higher tensile strength per unit area than those with larger diameters
(Martinez, 2013). In fact, studies have indicated that there exists an exponential increase
in root soil cohesion as fine root mass increases (Gyssels, et al., 2005).
Many IVS, like knotweed (Arnold & Toran, 2018), giant reed (Arundo donax)
(Stover et al., 2018), reed canarygrass (Martinez, 2013), or Himalayan blackberry (United
States Department of Agriculture [USDA], 2015) possess relatively shallow root systems
which do not bind soil as well as their native counterparts. Unbound soils can increase the
frequency of large-scale erosion events, translate to sediment inputs many magnitudes
greater than the maximum threshold permitted for freshwater salmon habitat, and reduce
salmon survival in a local area for up to several years (Waples et al., 2009). Severe
monocultures of IVS in areas of steep topography have even been linked to landslides
(Malik et al., 2016; Al Mahmud et al., 2018), which can render a stream impassible by
fish. Increased sediment loads to salmon bearing streams can limit available nesting
habitat, clogs gills, and lower survivability of fish (Close, 2015). A study published in
2014, in Access International Journal of Agriculture, found that native plants have most
often been the best option for slope stabilization and a feasible remediation method in
landslide prone areas (Lu, 2014).
As reiterated many times throughout this thesis, DO in Pacific salmon habitat
must exists in adequate concentrations in order to permit several necessary biological
functions in this species and enable the perpetuation of vital ecosystem services. The
ways in which vegetation may affect aqueous DO concentrations varies by species and
can be the result of biotic or abiotic processes. As previously explained in Chapter 2.3.2,

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Washington standards for DO in spawning, rearing, and migrating salmon range between
8.0 to 9.5 milligrams per liter for a one-day minimum (Finch & Brown, 2020). The
following section addresses some potential effects that vegetation can have on DO in
aquatic ecosystems and attempts to correlate IVS occurrence in Western Washington and
salmon habitat degradation.
Some emergent macrophyte species deplete oxygen in water by venting oxygen
produced during photosynthesis directly above of the water-air barrier, rather than into
the water column (Kuehne, 2016). A 2016 study indicated that the invasive emergent
macrophyte parrotfeather (Myriophyllum aquaticum) within the Chehalis River system
reduced DO concentrations to hypoxic levels in areas dominated by the plant; “The
lowest DO concentrations were observed in quadrats dominated by parrotfeather”
(Kuehne, 2016, p. 1853). An early study on Eurasian watermilfoil indicated that it
reduced DO during seasonal periods of senescence and subsequent decomposition (Aiken
et al., 1979). Other invasive plants, such as reed canarygrass, (Klopfenstein, 2016), giant
reed (Stein et al., 2000), and saltcedar (Stein et al., 2000), mechanically restrict water
flow to the point at which available DO is consumed by aerobic aquatic organisms faster
than it can be replenished (Mitchell-Holland et al., 2018). It has been established as
scientific fact that there exists a negative correlation between the water temperature and
solubility of DO (Fellman et al., 2018). Many IVS in Western Washington have the
tendency to form monocultures in the area of proliferation, which can reduce native tree
canopy cover and thereby increase solar radiation exposure to a water body.
It is possible for invasive plants to have a larger effect on an entire ecosystem, as
their proliferation can alter the local hydrology quite drastically. In Washington State,

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“…common cordgrass has transformed intertidal areas and gently sloping mudflats into
poorly drained marshes” (Simberloff, 2013). Several well-studied invasive plants
contribute allochthonous material to streams, rivers, and lakes which can alter many
characteristics of the local environment. The addition of organic material to freshwater
ecosystems by non-native plants can introduce novel chemicals that the native biology is
ill-equipped to cope with (Bottollier-Curtet et al., 2015). In a paper published in 2008,
Going and Dudley monitored and documented the laboratory growth and survival of the
aquatic saprophagous caddisfly (Lepidostoma unicolor) upon feeding on a diet of plant
litter native to the study site (white alder [Alnus rhombifolia], Frémont’s cottonwood
[Populus fremontii], and willow [Salix spp.]) versus non-native invasive plant litter
(saltcedar [Tamarix ramosissima] and giant reed). Going and Dudley concluded that giant
reed promoted significant reduction in caddisfly colonization and even induce high
mortality (~ 80%) in larvae, likely due to the plant’s production of alkaloid and sterol
compounds (2008).
In 2015, Bottollier-Curtet et al. analyzed the effect of invasive plant litter,
Japanese knotweed, in riparian areas on the diversity of detritivorous organisms, and
found that “…native microorganisms and invertebrates may have to face unusual
secondary compounds produced by exotic plants” (Ehrefeld as cited in Bottellier-Curtet
et al., 2015, p.266). Although, the authors found no significant correlation between
organism abundance/diversity and the particular exotic plant litter used (Bottollier-Curtet
et al., 2015). A separate similar study performed in Clear Creek Idaho arrived at the same
conclusion: “Japanese knotweed exhibited no differences from native leaf litter in either

60

decomposition rate or macroinvertebrate colonisation dynamics” (Braatne et al. 2007, p.
664).
The native mixed conifer/deciduous forests of the Pacific Northwest provide
shade to streams by their extensive canopy cover and decrease stream surface area
exposed to solar radiation. One of the greatest threats posed by IVS in riparian zones
along salmon habitat has been their tendency to outcompete and displace native tree
species. By doing so, non-native plant species can reduce native canopy cover and expose
large areas of salmon habitat to warming sunlight and predators (Zedler & Kercher,
2004). This reduction in canopy cover and increase in water temperature directly affects
the solubility of aqueous DO and limits the respiratory capacity of aquatic aerobic
organisms. This has crucial implications for Pacific salmon habitat as the species are
sensitive to low DO concentrations. Healthy riparian zones are especially important
within urbanized areas, particularly those which contain freshwater streams that support
salmon populations (May et al., 1998).
DO concentrations in salmon habitat can be altered by IVS in other ways besides
increased stream temperatures resulting from riparian canopy reduction. A paper
published in the journal Freshwater Biology in 2016 shows the devastating effects of the
notorious Pacific Northwest invader parrotfeather on local conditions of the Chehalis
River, a major salmon migration route (Kuehne et al.). The authors asserted that areas
proliferated by parrotfeather provide poor quality habitat for native species (Kuehne et
al., 2016). Relative abundance of native fishes in the river, including Pacific salmon,
were diminished around high concentrations of this invasive macrophyte, likely because
“DO concentrations were significantly reduced and approached hypoxic levels in areas

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dominated by parrotfeather [when] compared with native vegetation” (Kuehne et al.,
2016, p. 1846). The depleted DO concentrations in the Chehalis river system due to
parrotfeather proliferation are believed to be caused by mechanisms associated with
emergent floating-mat macrophytic species (Kuehne et al., 2016). These mechanisms
include the minimal rate of photosynthesis and venting of oxygen directly into the air
rather than the water column (Kuehne et al., 2016).
Invasive plants can affect the chemistry of a freshwater environment either
directly or indirectly. Direct chemical inputs to an aquatic ecosystem by IVS can include
contributing allochthonous materials during seasonal senescence (Urgenson, 2006),
exudation of allelopathic compounds (Murrell et al., 2011), or by altering nutrient cycling
regimes (Corbin & D’Antonio, 2012). The effect of natural plant toxicity, another aspect
of chemical alteration to salmon habitat, warrants future research. Species such as poison
and water hemlock have a notable presence in Washington state, can grow within riparian
zones, and have been found to be toxic to both humans and animals (NWCB, 2017).
Research conducted on the effects of toxic phytocompounds on Pacific salmon habitat is
currently limited and wide knowledge gaps exist on this subject.
Indirect effects that IVS may have on the chemical composition of an ecosystem
often manifest as a result of alterations to the physical structure of the local environment.
Invasive plants that commonly establish severe monocultures have the capability of
drastically changing the environmental foundation. IVS, such as Himalayan blackberry
(Bennett, 2006), English ivy (Ingham, 2008), and knotweed (Urgenson, 2006), regularly
form monotypic stands in Western Washington and can effectively suppress the growth
and development of native vegetative species. By suppressing native vegetation, either

62

through allelopathy, hyper competitiveness, or nutrient appropriation, these IVS may
reduce the native tree abundance in a riparian zone and limit the efficiency of several
riparian ecosystem functions which are beneficial to salmon species.
Natural riparian zones exist as considerably diverse ecosystems which provide
several services, including filtering of surface and ground water, bank stabilization by
vegetation, as well as buffering a stream from toxic stormwater runoff and aerosol drift
pollutants (Everest & Reeves, 2007). Riparian ecosystems are efficient at trapping,
binding, degrading many common types of pollutants, including phosphoric and
nitrogenous chemicals, hydrocarbons, heavy metals, polychlorinated-biphenyl
compounds, as well as agricultural chemicals (Desbonnet et al., 1994). Severe
degradation to riparian zones may further compromise the health of the local aquatic
ecosystem which they envelop by allowing excess toxins and contaminated particulate
matter to easily enter the water column. May et al. (1998) submitted a comprehensive
analysis on the ecological benefits of riparian zones in urban settings in the Pacific
Northwest region. By performing extensive multi-parametric analyses on water samples
in the Puget Sound ecoregion and taking comprehensive riparian zone vegetative
inventories, the researchers of this study provided substantial unequivocal data that
demonstrated the function of healthy riparian zones in providing suitable Pacific salmon
habitat (May et al., 1998).
Aside from the previously mentioned ability of some IVS to suppress native
vegetation, there remains a concern of alterations to species composition, diversity, and
abundance of an ecosystem. Introduced vegetative species tend to support different
dependent organisms than those of native vegetative species. There have been several

63

recent studies that indicate there is often a negative correlation of IVS and species
diversity at the ecosystem level (Colleran & Goodall, 2013; Going & Dudley, 2008;
Simberloff et al., 2005; Weilhoefer et al., 2017).
One example, is a 2008 study by Going and Dudley which examined the
colonization characteristics of an aquatic detritivorous invertebrate shredder-species on
native leaf litter versus non-native leaf litter. This study found that the aquatic caddisfly
(Lepidostoma) larvae showed preferential feeding habits towards the native vegetation
litter, such as white alder and willow. The larvae selectively fed on leaf margins of the
non-native vegetation, giant reed, and avoided other parts altogether. Whereas the
invertebrate indiscriminately consumed all portions of the native vegetation.
Similarly, Klopfenstein (2016) conducted research on salmon habitat in partially
and fully restored sites within the Lower Columbia River floodplain. By taking surveys
of vegetation types and performing feeding experiments in artificial enclosures, the
researchers determined that an invasion of reed canarygrass in the Columbia River
estuary altered the abundance and diversity of many species of energy-rich invertebrates
which juvenile salmon depend on for growth and development (Figure 8) (Klopfenstein,
2016). The IVS-induced change to invertebrate diversity and abundance translated to a
seasonal growth variance, between juvenile salmon feeding in enclosures dominated by
reed canarygrass and native vegetative cover, by as much as approximately 29%
(Klopfenstein, 2016).

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Figure 8: Chinook size variances across two habitat types
This two-year study was conducted on the Columbia River just northwest of Portland, OR in the Multnomah Channel Marsh Natural
Area (MCM) and compares salmon growth and diets in areas dominated by reed canarygrass (referred to as PHAR in this study) to
areas dominated by native vegetation. This figure displays those growth characteristics in both habitat types across two years, 2015
and 2016; illustrating that the chinook displayed more growth in areas dominated with native vegetation than in reed canarygrass
infested areas (Klopfenstein, 2016, Figure 9).

There exists a wealth of research regarding knotweed and its effects on
invertebrate populations. Yet, the determination on whether or not the invasive plant
diminishes biodiversity differs widely between studies. While some studies indicate that
knotweed may contribute organic material that fulfills a detrital function similar to native
vegetation (Braatne et al., 2007), other studies indicate a pronounced negative correlation
of invertebrate biodiversity and knotweed presence (Claeson et al., 2014; Gerber et al.,
2008). Knotweed presence has even been linked to a reduced growth potential of a green
frog species (Rana clamitans) native to New York State (Maerz et al., 2005). Based on
the literature gathered in this thesis, knotweed related impacts to native vegetation
diversity and abundance appear to be more common than the invasive plant’s effects on
invertebrate, amphibian, or faunal populations. Pacific salmon habitat restoration efforts

65

would benefit greatly from future research into knotweed’s effects on invertebrate species
that salmon rely on for growth and development.
The potential of IVS to significantly impact Pacific salmon habitat has been well
established through previous research efforts. The available literature on the subject has
demonstrated a great need for natural habitat restoration as the first step to preserving this
iconic species. The role of invasive plants in the destruction of salmon habitat in Western
Washington must be addressed as a high priority element of future management plans.

2.4 Stakeholder Relationships
The degree of efficiency in which entities cooperate to accomplish mutual goals
can determine the ultimate outcome of a particular situation. Good working relationships
are based on trust, equality, and respect. For interrelated parties to work effectively
together in achieving common objectives, there needs to be transparency of information,
alignment of values, dedicated individuals, and flexibility. Each constituent of the
partnership must keep the group’s interests at the forefront of their agenda and be able to
make compromises when needed, in order to accomplish the greater good. The following
section will feature some of the challenges of interagency relationships, as well as
provide examples of good stakeholder relationships, in the practice of land management
and Pacific salmon conservation.

2.4.1 Communication/Collaboration
A major challenge when managing invasive species and protecting riparian
habitats has long included the inability to effectively communicate across stakeholders.
Lackey postulates key points in his 2003 article about forecasting Pacific Northwest
salmon populations into the year 2100, claiming that serious changes in society must
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occur if wild salmon runs are to be restored. He articulates his belief that society’s failure
to effectively manage salmon habitat derives from policy conundrum, by stating that even
though a strong majority is in favor of taking action to preserve the species, preexisting
deeply entrenched policy stances by established bureaucracies convolute and obstruct the
process (Lackey, 2003). Furthermore, Lackey believes that the salmon conservation
debate has been politicized to the point of which policy preferences and political
affiliation have become more of a focus than scientific fact and objective reasoning
(2003). Lackey’s (2003) statements exemplify many of the difficulties experienced
between concerned parties regarding the importance of salmon preservation.
Various groups/agencies have conflicting perspectives about the priority of their
interests. Although, each party has valid arguments, compromises must be made for
salmon populations to survive. Malick et al. have identified other difficulties in the
interdisciplinary approach to salmon habitat management; stating that “Ecosystem
openness presents a [challenge] to integrating highly migratory species into [ecosystembased management (EBM)] policies because these species frequently move across
ecosystem and jurisdictional boundaries” (2017, p. 123). Because of this fact, there can
be ambiguity with understanding which local agency/department has operational status.
For example, a salmon migration route which spans private, public, and tribal lands is
often the topic of policy disagreements between stakeholders. In these instances, it can
be common to see fragmentary or partial restoration sites.
In 2014, Sara Breslow wrote an insightful article for Anthropological Quarterly in
which she describes many of the incongruities between private landowners and
environmental advocates surrounding the topic of salmon habitat restoration. In her

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submission, Breslow focusses on a case study which occurred in the Skagit River Valley
of Washington State, where various state agencies, two state-supported salmon habitat
restoration groups, and other environmental organizations worked in concert with local
tribes to persuade farmers to convert part of their land to suitable salmon habitat. The
tribes “…produce[d] scientific research in support of fisheries management and salmon
recovery by hiring teams largely comprised of non-native biologists…” (Breslow, 2014).
The restoration strategies proposed by the project developers include planting of trees
along streams, removing and setting back dikes, removing and modifying culverts and
tide gates, recreating spawning channels, and adding stream structure by anchoring logs
into riverbanks. Most of the farmers approached with this proposition had demonstrated
significant resistance, stating that the project failed to consider “…ecological processes,
such as invasive species and local drainage and flooding patterns…” (Breslow, 2014, p.
728). Some landowners have even expressed outrage and claimed that the scientific data
tends to be biased towards abstract anti-farming assumptions. Although ample evidence
remains for the need to restore salmon habitat, some of these landowners adopted a
defensive stance when asked for their cooperation. Interviews conducted by Breslow
revealed that the farmers’ defiance seems more to do with the perceived feeling of
disrespect rather than disagreements with the scientific methods employed in the project
(2014). Farmers coalesced around a defensive position and opposed this project proposal
by writing letters to the editor of a local paper, bringing their arguments to the courts, and
successfully lobbying against changes to the state’s hydraulics code. By employing
social, economic, and cultural counter-arguments, the farmers gained the full support of
county officials. To date, this project effort has gained little traction in the local farming

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culture, and the breadth and scope of its aspirations have not yet materialized. Though,
this study highlights some of the difficulties experienced when pleading the case for
salmon habitat restoration.

2.4.2 Relationships with Salmon
It is feasible to claim, based on the information covered in this literature review,
that stakeholders of salmon habitat restoration fall into one of four groups: economic,
tribal, environmental, private. Each of those constituents hold their own unique
perspective on the topic. A substantial portion of Washington State fisheries businesses
have an inextricable dependance on Pacific salmon. In fact, all levels of
fishermen/women, from Washington businesses to individuals, are affected by Pacific
salmon conservation legislation on some level. Businesses operating in the state are
required to adhere to strict environmental regulations, many of which have been strongly
influenced by salmon restoration efforts, such as the water quality standards, and land use
restrictions set by the Washington State Department of Ecology (see Table 2). Many of
the indigenous tribal organizations of Washington State are interconnected with salmon,
and rely on them for cultural, subsistence, and economic reasons (Colombi, 2012; Cronin
& Ostergren, 2007; Dillon, 2020). The U.S. Supreme Court upheld the Boldt Decision to
grant Pacific Northwest indigenous people legal rights to fifty percent of harvestable fish
(Blumm, 2017; Brown & Footen, 2010; Donovan, 2016). Several federally recognized
state tribes still practice cultural ceremonies during the major seasonal salmon runs and
regard these animals as sacred. In addition to providing a food staple to indigenous
peoples, salmon have been a major part of tribal economy for thousands of years
(CRITFC, 2016).
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2.4.3 Stakeholders and IVS
Concerned parties of noxious weed invasion exist in all sectors of Washington
State society. IVS impact private landowners by damaging infrastructure, posing a risk to
health, and decreasing property value (NWCB, 2018). Industries such as forestry and
farming are commonly impacted by IVS. Timber lands can become particularly
vulnerable to IVS as they are often the site of soil disturbance from logging practices,
which non-native plants can readily establish. A study by Slesak et al. provides
statistically significant evidence of suppression by Scotch broom on Douglas-fir forests
of the Pacific Northwest (2016). As previously stated in this literature review,
agriculturists experience impacts due to IVS in a direct effect on profitability and reduced
crop production (NWCB, 2018).

2.4.4 Perceptions and Controversies
Invasive Vegetative Species (IVS) management suffers from a lack of clearly
defined terms. Lackey (2003) explained how certain terms prevent management from
progressing; for example, different groups have different ideas for what constitutes
‘ecosystem health’, so they continue to debate the terms’ definition. Lackey also provided
evidence of backlash to the Endangered Species Act concerning salmon populations,
specifically regarding the inability to protect salmon without impacting humans or
changing human behavior, as well as the inability to protect salmon when completely
ignoring human needs (Lackey, 2003). This debate can lead to bias on the part of some
agendas.
Drs. Mark Sagoff and Daniel Simberloff have had a long rivalry and debated the
terms and the management of IVS. One of the recurring themes of their debates concerns
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the term, ‘environmental harm’. Dr. Simberloff has advocated for invasive species
control whereas Sagoff states that management based on this concept typically remains a
waste of time and resources (Sagoff, 2009). While Sagoff (2009) stated that he agrees
that controlling invasive vegetation is warranted when it causes ‘economic harm’ or
‘harm to human health’, he also states that ‘environmental harm’ exists as an imaginary
concept (Sagoff, 2005 & 2009), that it cannot be used in science, and even considers it to
be ‘diktat’ and ‘diatribe’. Thus, Sagoff argued that management cannot be justified for a
species based on this concept. Sagoff (2009) also proposed that ‘environmental harm’ is
based solely on opinion set by those who are ‘offended’ or ‘do not like’ the species.
According to Sagoff, “Science on occasion may be able to tell us what is false or true[,]
but it can never tell us what is bad or good” (2009, p.84). Sagoff added that a biodiversity
increase may result from the invasive species adding pressure to the native counterparts
(Sagoff, 2009); while there is always the ‘exception to the rule’, IVS tend to establish
towards creating a monoculture of the species – the very opposite from being bio-diverse.
Sagoff (2018) made a claim that when differentiating between the terms of
‘invasive’ or ‘colonizing’ species as well as between ‘established alien’ and ‘native’
species that we need to remove the human component and the time of arrival in the
definition; however, humans are very much a part of the ecosystem and thus must be
included. Also, the time of arrival certainly makes a difference in determining specific
terms of a species nativity. Sagoff held his position about an invasive species posing
‘ecological damage’ as something that “cannot possibly be tested because [it] is a
normative idea that can mean almost anything” (2018, p. 28). On the contrary, each of
Simberloff’s articles supported management and control of invasive species without any

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terminological confusion. This can be especially evident when Simberloff, Parker, &
Windle (2005) stated that with more research, better technologies, and innovative
approaches IVS have a real chance at being detected early, managed quickly and
efficiently, as well as eradicated in many instances. Simberloff, Parker, & Windle (2005)
insisted that all this potential success for management does not fall within the realm of
fiction.
Allendorf and Lundquist (2003) discussed the long-standing controversy in
invasion biology, typically referring to a debate over the need to manage for such species.
Proponents of invasive species management have often relied on terminology which has
been deemed by some scientists as confusing or vague to support their position. Allendorf
and Lundquist also argue that non-native species have invaded throughout history and
that natural systems adapt to the invaders. The statement “There are many unknowns, but
[a] lack of information should not stop scientists from influencing such decisions”
(Allendorf & Lundquist, 2003, p.26) provided a strong argument for the advancement of
invasive species management. Ruckelshaus et al. simplified interagency disputes by
stating that, “our charge as scientists is to respond to the intense pressure for biologically
defensible answers in a way that clearly distinguishes scientific conclusions from policy
choices” (2002, p. 667).
The literature featured within this thesis provided a wealth of knowledge
concerning the relationship between Pacific salmon and the occurrence of invasive
vegetation in the Pacific Northwest. Through the investigation of previous scientific
endeavors and in-depth research studies, this project has shown the importance of
effective IVS management for protecting and maintaining salmon habitat. The

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information established the prominence of salmon in Western Washington’s
environment, society, indigenous cultures, and economy. It also provided an extensive
background of Western Washington’s invasive plant species and their role in natural
systems. Furthermore, the effect of IVS on freshwater habitat has been established to
contribute significantly to the decline of salmon populations. Knowledge gaps do exist,
specifically related to the impacts of noxious weeds, which can only be satisfied through
future scientific research. As science gains more understanding into the subject, various
agencies invested in salmon conservation and land management may be better equipped
to address the problem of an iconic Pacific Northwest fish species’ declining population.

Chapter 3: Methods
This methods section has been broken up into various sub-sections and organized
chronologically by the order of completion for this thesis project. These sections include
the creation of the support team as well as methods for the survey creation and
distribution, survey analysis, and post-survey literature review and analysis.

3.1 Team
I initially met with Justin Bush, the Executive Coordinator for the Washington
Invasive Species Council (WISC), who suggested this thesis topic and later began
introducing me to those who would ultimately become part of my team of field experts.
This team was designed to provide professional support, maintain proper focus, and
supplement my research with data and resources. Those who initially joined the group
include Justin Bush with WISC, Mary Fee with the Washington State Noxious Weed

73

Control Board (NWCB), Chad Phillips with the Washington State Department of
Agriculture (WSDA): Pest Program, Alice Rubin with the Salmon Grants Section of the
Recreation and Conservation Office (RCO), as well as Lizbeth Seebacher and Jenifer
Parsons with the Washington Department of Ecology (Ecology). This team was later
joined by Irene Weber as a Vegetation Ecologist with the Washington State Department
of Natural Resources (DNR), as well as Angela Dillon and Caleb Graham with the
Puyallup Tribe Fisheries (PTF). Once the survey was collected, new additions to this
team included: Danny Najera, PhD, biology instructor at Green River College (GRC);
Patricia Grover, Mason County NWCB; Gavin Nishiyori, West Fork Environmental;
Susan Bird, Yakima County NWCB; Jennifer Mendoza, Cowlitz County NWCB; Sarah
Zaniewski, Squaxin Island Tribe; Jeff Nesbitt, Pacific County NWCB; Marty Hudson,
Klickitat County NWCB; Kiley Smith, Grays Harbor NWCB; and David Heimer,
Washington Department of Fish and Wildlife (WDFW).

3.2 Survey
This survey involved a multi-step process requiring approval for implementation.
As a first step in the process for this research, I completed a Human Subjects Review
(HSR), detailing the purpose and objective of this study. The HSR was approved on July
15th, 2020 by The Evergreen MES Human Subjects Review committee. Once the HSR
was approved, the creation, distribution, and analysis of the survey followed.
The survey (see Appendix A, C, & D) consisted of three parts: Part 1 (Appendix
A) provided the introduction to the survey, Confidentiality Agreement, Letter of Interest,
and optional demographic information; Part 2 (Appendix C) consisted of the survey

74

body which will soon be discussed in more detail; and Part 3 (Appendix D) included
feedback on the survey itself.
After completing Part 1 of the survey, respondents were asked to select a single
invasive vegetative species from a list of 52 possible species within Washington
(Appendix B). This list was generated from a broad list of candidates using the NWCB
website for Class A, B, and C invasive weeds. Once a species had been chosen, the
respondent was directed to Part 2 of the survey; a page for that specific species and asked
a series of questions relating to its location, extent/abundance, potential future
impact/spread, and current level of control for that plant, as well as research availability.
Respondents also had the option to provide any additional comments, concerns, or
suggestions for that species (such as any Water Resource Inventory Area (WRIA)
information or information about multiple county locations for that species).
I chose to group the data by county because the majority of respondents were
more familiar with county level operations than on the WRIA level. Making the questions
more relatable to the group majority allowed for more respondents to finish the survey.
However, salmon information may be more relevant to watershed boundaries than at the
county level. This sacrifice of WRIA data, which could potentially provide for more
appropriate data to the study, is justified by the possibility of a larger sample size.
However, a follow up email to those who received the survey was issued shortly after the
distribution, as the questions regarding infestation, impact, and control (see Questions 10,
11, & 12 in Appendix C) had referenced the previously designed watershed format
instead of county distributions. This email was intended to inform the recipient of the

75

survey to disregard the word ‘watershed’ in the relevant questions and substitute it for
‘county’ instead.

3.3 Survey Distribution
This survey was distributed as a judgement sample. A judgement sample is when
the researcher decides who the survey is distributed to and based on their own judgement
(businessjargons.com, 2016). The justification for this type of sampling was to narrow
the respondents to those with invested interest in the subject matter in order to create
more accurate results since the survey focused on a very narrow field of study.
With the help of the NWCB Executive Secretary, Mary Fee, I used the NWCB
Survey Monkey account to administer the initial survey. I sent the original email to my
team members in January of 2021. The Team each had a copy of the SurveyMonkey link
and then forwarded the email to various professionals within their agency/professional
listservs; for instance, Mary Fee was able to send the link to each of the County NWCBs.
Each of the pre-survey team members were able to choose recipients at their own
discretion based on who they determined to be a “best fit” candidate for taking the
survey. They were also encouraged to ask their recipients to redistribute the survey where
applicable. I too included the same SurveyMonkey link in emails from my personal
account which were distributed to my undergrad professors, who spend many hours in the
field collecting data with students, fellow alumni from my undergraduate institution, who
currently work in the field at various agencies, and other professional contacts which I
felt were appropriate for this study.
The initial distribution occurred between January 13th and 15th of 2021; the
respondents were given until February 1st, approximately two weeks, to complete and
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submit their responses. Initially, there were very few returns on the survey, thus limiting
the sample size and making it very hard to draw any conclusions about a top number of
IVS. As a result, the deadline became extended into late-March and new recipients were
included to take the survey.

3.4 Survey Analysis
The purpose of the survey was to narrow down the list of 52 potential invasive
vegetative species found in Western Washington (Appendix B) to a more manageable
number of approximately five species (Table 4). The narrowing down of the list was
achieved by focusing on the species mentioned most often by the respondents. In essence,
the species selected by respondents may not represent their true abundance. It is possible
that respondents based their choices on their familiarity with them, visual abundance, or
for more scientific reasons. Nonetheless, this thesis is designed to value the perspective
of field experts, assuming a certain degree of professional integrity and individual
competency relating to their respective disciplines. To understand the choice of species, a
question was included asking the respondents for reasoning behind their choice. To
further account for the bias, I examined literature pertaining to each of the top species and
discuss this further in Ch 4.
The literature review explored various criteria and environmental conditions
proven to be important for salmon survival needs. These criteria, also briefly explained in
Chapter 2.1.2 and Chapter 2.3.1, includes overall biodiversity, sediment loads, stream
chemistry, water flow regimes, stream temperatures, shelter abundance, migration route
obstruction, and predator habitat.

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Once the post-survey literature review was completed, a comparison between
survey results was analyzed and examined in Ch 4. Information gaps, created by the lack
of available scientific literature, on the impact an IVS has on salmon habitat were also
noted (Table 5). The results on the impact these invasive species have on salmon survival
is detailed in Chapter 4. Each of the top species has its own dedicated sub-section, where
the survey results are compared with relevant scientific literature.

3.5 Mapping
Multiple data layers were created in ArcGIS Pro and uploaded to ArcGIS Online
for further analysis. County shapefiles were collected from Washington Department of
Natural Resources GIS Open Data Portal. There are 19 counties selected from this
shapefile and used to represent the study area as well as to analyze the locations of
salmon streams and IVS presence within Western Washington (Appendix E1).
Salmon-bearing streams were downloaded from SalmonScape’s website
(Washington Department of Fish and Wildlife [WDFW], 2020). Salmon streams were
filtered by species and represented with unique colors to each species as it pertains to
their spawning (darkest tint), rearing (middle tint), and migration/presence (lightest tint)
(Appendices 2 – 7 & 9 – 14). It is important to note that there is a disclaimer with this
data; for instance, the data represented may not be complete due to insufficient staff
availability, funding constraints, and changes in populations which may occur over time
(WDFW, 2020).
The top four IVS species were selected from EDDMapS website and downloaded
as specific points for estimating each species locations (Appendices E8 – E14)
(UGCISEH, 2020). The IVS points are represented as a flag with a unique color value to
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each species. EDDMapS is a software application created by members of the Center for
Invasive Species and Ecosystem Health at the University of Georgia (UGCISEH, 2020).
This application can be downloaded to a smartphone or tablet allowing the general public
to find, map, and track invasive species in their area, which becomes verified by
professionals in the field before becoming available for access to view and/or download
(UGCISEH, 2020). While this can be a great tool for early detection and rapid response
(EDRR) of invasives in an area, there remain limitations. Some of these limitations,
similar to the SalmonScape data, include the lack of available resources for verifying
species (such as available personnel, time, or funding), a lack of public awareness and/or
knowledge in identifying certain species, a lack of awareness to the application itself (not
everybody knows this app exists), or limitations in mobility (not all areas where IVS
prevail are easily accessed by the public) (UGCISEH, 2020). Thus, this data serves as
starting points for restoration projects, but do not necessarily reflect the true population of
invasive species.
After the collection of each of these types of data (county, salmon streams,
invasive vegetation location), they were analyzed in various maps that show their
approximate locations (salmon are represented in Appendices E2-E7 and IVS in
Appendix E8) and relations to one another (Appendices E9-E14). The proximity
analysis was based on a 61-meter (200-foot) buffer between IVS locations and salmon
stream segments. This buffer was selected in accordance with the Forest Practices
Illustrated manual for Washington’s riparian buffers (Washington Department of Natural
Resources [WA DNR], 2021).

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Chapter 4: Results & Discussion
Based on the survey results, the four most frequently mentioned for highest
priority of noxious weeds within Western Washington included knotweed (all four
knotweed species in general but with preference for Japanese knotweed), reed
canarygrass, yellow flag iris, and Brazilian elodea (Table 4). According to surveyed
individuals, knotweed appears to have the most research available for sufficiently
meeting the needs of their agencies/organizations/etc. Responses concerning reed
canarygrass research availability fluctuated widely. Both yellow flag iris and Brazilian
elodea were suggested as understudied (Table 5).
Table 4: Survey Results and Ranking of top IVS
This table displays the number of votes for each of the highest ranked species. These counts are generated from the survey. The
columns are defined below:
➢ “Rank” shows which species was counted the most times within the survey
➢ “Common” displays the common name for the species on the survey
➢ “‘Class” depicts the invasive species’ national classification system based on abundance
➢ #’s “1” - “6” illustrate whether an individual noted the species first through sixth as the respondents ranked them within their
survey, and the count within those columns is based on how many individuals chose that ranking for the correlating species.
➢ “NC” is the ‘no-count’ column is for individuals that picked a species in the survey but did not include them in the ranking process.
➢ “Total” was then sorted from most to least allowing for a ranking of the top (including the NC’s).

Table 5: Percentage of available research by species
This table illustrates how much research on each IVS is perceived to be available to various agencies/organizations/groups/etc. This
question is based on “Question 13” from the survey as shown in Appendix C: Survey Part II.

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Japanese knotweed, a class B noxious weed, appears in 95 total locations (Table
1 and Appendix E8). When search parameters are limited to a an approximate 61-meter
(200-feet) buffer of each other, knotweed appears within 22 locations across eight of the
counties (Table 6 and Appendices E9-E14). Reed canarygrass, a class C noxious weed,
has been documented in 108 total locations (Table 1 and Appendix E8). When search
parameters are limited to the same buffer amount, reed canarygrass appears within six
locations across four of the counties (Table 6 and Appendices E9-E14). Another class C
noxious weed, Yellow flag iris has been found in 284 total locations (Table 1 and
Appendix E8). When search parameters are limited to the buffer amount, yellow flag iris
appears within 68 locations across 15 of the counties (Table 6 and Appendices E9-E14).
Furthermore, Brazilian elodea, a class B noxious weed, has 113 total documented
locations (Table 1 and Appendix E8). When search parameters are limited to the buffer
amount, Brazilian elodea appears within 24 locations across nine of the counties (Table 6
and Appendices E9-E14).

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Table 6: Top IVS within 200 feet of salmon streams
Table illustrating the number of IVS found within 200-feet of salmon streams within Western Washington. These amounts have been
mapped and can be seen in Appendices 9-14.

Many studies have documented the direct biodiversity impacts of knotweed and
reed canary grass. The direct impacts of Brazilian elodea and yellow flag iris on overall
biodiversity are understudied, but there remains a vast amount of literature on indirect
impacts, such as specific traits that could make them better competitors. Sediment is also
well studied in knotweed and reed canarygrass while understudied in yellow flag iris and
does not apply to Brazilian elodea. Impacts on stream chemistry is well studied in
knotweed and Brazilian elodea, but underrepresented in reed canarygrass, mostly
inconclusive in yellow flag iris. Disruption of water flow is typically a widely accepted
trait among all four of the IVS but appears to be very underrepresented in quantitative
data. Shelter abundance effects are a tricky category to synthesize in available literature
since they are mostly an indirect effect caused by IVS outcompeting any native
vegetation that would normally provide DWD or cover. Migration route obstruction is
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better studied in reed canarygrass and yellow flag iris and largely unexplored in
knotweed or Brazilian elodea. Promotion of salmon predator habitat is not applicable to
knotweed or yellow flag iris but has been observed in literature for reed canarygrass and
Brazilian elodea. There was difficulty in exploring information regarding IVS as salmon
predator habitat, because it requires preexisting knowledge of salmon predator species in
freshwater stream environments in order to do a complete investigation.

4.1 Knotweed (Fallopia spp.)
The four species of invasive Knotweed found in Washington include: Japanese
(F. japonica), giant (F. sachalinensis), Himalayan (Persicaria wallichii), and Bohemian
(F. x bohemicum). The total allotted budget for Washington State’s knotweed
management program was $950,484 over the course of two years (2017-2019). That
funding was spent managing 835.2 miles of riparian ecosystems, of which 469.2 miles
were located in Western Washington counties (Washington State Department of
Agriculture [WSDA], 2017). The taxonomic designation of knotweeds has often been the
subject of debate, as they are categorized within several genera (i.e., Fallopia,
Reynoutria, Polygonum, and others). This thesis will use the most recent North American
nomenclature associated with knotweed, Fallopia. These rhizomatous, herbaceous
perennial plants range in size from 1.5 meters (~ 5 feet) to 5 meters (~ 16.5 feet) in height
(Parkinson & Mangold, 2010). Due to the climate of the Pacific Northwest region,
knotweed experiences accelerated growth in early spring, usually around April, with its
first flowers appearing in late summer, and a complete dieback of the plant occurs soon
after the first frost. (McHugh, 2006). The four species can be easily distinguished from
one another by their different leaf sizes (Figure 9).
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Figure 9: [photo] Knotweed leaf identification
Differences in knotweed leaf sizes compared between species (Knotweedkillers.com, n.d.).

The biological traits inherent to this aggressive plant promote its ability to harm
local ecosystems by degrading riparian ecology, causing stream bank erosion, as well as
negatively affecting native vegetation, wildlife, and salmon habitat (Andreas &
DesCamp, 2015). The ability of knotweed to hybridize with similar knotweed congeners
may provide it with a competitive edge over native vegetation. Japanese and giant
knotweed have cross bred to create a successful hybrid, Bohemian knotweed, commonly
found in Washington State. In a controlled greenhouse experiment, Parepa et al. (2014)
compared the competitive behaviors of Japanese and giant knotweed to their hybrid,
Bohemian knotweed. The researchers discovered that the hybrid generally outperformed
either parent plant in terms of growth and development, fragment regeneration,
competitive behaviors, and overall success (Parepa et al., 2014).
The rhizome network of knotweed, which can extend to a depth of 4.5-meters and
laterally by 20 meters (approximately 15 by 65 feet), possesses characteristics that have

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enabled its aggressive clonal reproduction and hyper competitiveness (Jones et al., 2018).
These invasive plants can easily reproduce from root and stem fragments less than 2.5
centimeters (1 inch) in size (McHugh, 2006; Urgenson, 2006; Harbaugh, 2017). Research
conducted by Colleran & Goodall (2014) indicated that approximately 70% of the
Japanese knotweed clones observed in natural settings had sprouted from rhizome
fragments, and their subsequent laboratory experiments confirmed this regeneration rate.
Knotweed has been observed sprouting from rhizome fragments 20 years after the
complete removal of its surface material (Stuart, 2015). While all four knotweed species
listed will be discussed, Japanese knotweed will be given priority as it has the most
research associated with it (Figure 10).

Figure 10: [photo] Japanese knotweed identifiers
Identifying characteristics of Japanese knotweed (Olaf B. et al., n.d.).

Knotweed ranked the highest from the survey results, with 67% of respondents
mentioning this genus as having a high impact on freshwater ecosystems. When asked
why this plant was specifically a priority, respondents mentioned that knotweed:

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1) outcompetes native species thus reducing biodiversity as well as preventing
species that would otherwise provide better canopy cover and shelter (80% of
knotweed respondents),
2) grows rapidly as a highly aggressive invader (60%),
3) causes soil instability which increases erosion rates and sediment (50%),
4) is common along streams (40%),
5) has roots that can alter stream morphology (30%),
6) is difficult to remove (20%),
7) can be costly to manage with limited and intensive options (20%),
8) increases water turbidity (10%),
9) increases flooding events (10%), and
10) reduces food availability for macroinvertebrates (10%).
The survey responses indicate that this highly invasive species drastically degrades
natural riparian conditions to the point which management becomes a top priority.

4.1.1 Dichotomy
The following dichotomy is taken directly from the second edition of the book,
Flora of the Pacific Northwest (2018), in which the genus Fallopia for giant, Bohemian,
and Japanese knotweeds begin on page 330, and the genus Persicaria for Himalayan
knotweed begins on page 331 (Hitchcock & Conquist, 2018). This dichotomous
breakdown of the plants allows for a deeper look into the plants ‘personality’.
Fallopia (p. 330)
Flowers perfect or some to all pistillate or staminate, inflorescence spikelike,
panicle, or racemose; pedicels not jointed at tip; perianth 5-parted most of length
or only near tip, greenish, white, or pink, outer tepals winged or keeled, largest;
stamens 6-8; pistil 3-carpellate; stigmas capitate, fimbriate, or peltate; fruit 386

angled; annual or large perennial herbs, some twining, or woody climbing vines;
stipules light to dark brown; leaves alternate, cauline, never jointed at base. Many
noxious weeds.
1b. Stems erect; stigmas fimbriate
3a. Veins of leaf underside with multicellular hairs (15x); midstem leaf bases deeply cordate; inflorescence much lower than
subtending leaf; riparian zones, roadsides, meadows, ditches;
aggressive Asian intro, escaped from cultivation; both sides
Cascades, Alaska to California, east to Atlantic coast; giant
knotweed (P.s.)
3. F. sachalinensis (F. Schmidt) Ronse
Decr.
3b. Veins of leaf underside scabrous or with simple hairs (15x);
mid-stem leaf bases slightly cordate to truncate or slightly cuneate;
inflorescence above or below subtending leaf
4a. Veins of leaf underside with scattered, simple, stoutbased hairs; mid-branching leaf base usually slightly
cordate; well-developed mid-stem leaves usually greater
than 20 centimeters long; riparian zones, roadsides,
wastelots; aggressive Asian intro, escaped from cultivation;
Alaska to Oregon, east to Montana and scattered east to
Atlantic coast; hybrid knotweed [aka Bohemian knotweed]
hybrid of 3 [giant k.] x 5 [Japanese k.]
4. F. xbohemica (Chrtek & Chrtova) J.P. Bailey
4b. Veins of leaf underside minutely scabrous with
scattered swollen cells or knobs; mid-branching leaf base
truncate (rarely slightly cuneate); largest mid-stem leaves
over 18 centimeters long; aggressive Asian intro, escaped
from cultivation, riparian zones, roadsides, wastelots;
Alaska to California, east to Atlantic coast; Japanese
knotweed
5. F. japonica (Houtt.) Rouse decr.
Persicaria (p. 331)
Flowers perfect; inflorescence capitate, spikelike or panicle; pedicels not jointed
at tip, or absent; perianth 4-5-parted about 1/5-2/3 length, greenish, white, pink,
red, or purple, outer tepals unkeeled and largest; stamens 5-8; pistil 2-3 carpellate;
stigmas capitate; fruit 2-3-angled; annual or perennial herbs, subshrubs; stipules
green to brown; leaves alternate, mostly cauline, never jointed at base, often with
a dark triangular mark. Plants of little or no grazing value; many noxious weeds.
1b. Stem smooth; leaf blade base usually truncate to tapered, rarely cordate but
then not clasping stem.
2b. Petioles unwinged; inflorescence usually more elongate in spikes or
panicles; anthers pink to red or purple
3a. Inflorescence a branched panicle; stigmas 3, achenes trigonous;
tepals 5, spreading, white (rarely faint pink); rhizomatous
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perennial, 7-25 decimeters; leaf blades 9-22 centimeters;
floodplains, roadsides, disturbed ground; Asian intro; west
Cascades, Alaska to California, mostly near coast; Himalayan
knotweed
3. P. wallichii (Greuter & Burdet)

4.1.2 Overall Biodiversity (Flora, Fauna, Invertebrates)
Knotweed species possess a host of evolutionary adaptations which may provide
the plant with several environmental advantages over native flora. These biological traits
and physical attributes converge to make this plant one of the most ecologically
destructive organisms in Western Washington. Knotweed’s rapid growth potential,
efficient use of nutrients, tolerance for environmental stresses, and hyper-competitive
nature enable this IVS to infest vast areas and drastically reduce native biodiversity.
Knotweed demonstrates a considerably high growth rate when compared to competitor
species, which allows it to grow taller, develop greater foliar surface area, and form
underground tissues faster than most competitors at the same stage of development.
Knotweed has been documented to grow as much as 15 centimeters (6 inches) per day in
early spring (Urgenson et al., 2009; Bailey et al., 2009). By growing taller than its
competitors, knotweed gains unobstructed access to sunlight and establishes
photosynthetic dominance.
The biological functions which provide knotweed with a high growth potential
reside in its rhizome network. The manner in which this plant utilizes carbon and
nitrogen is vastly superior to most Pacific Northwest native species. Prior to leaf-fall,
knotweed begins transferring the majority of their foliar nutrients to rhizome tissues for
storage; in this way, the species utilizes carbohydrate reserves the following spring for
instantaneous rapid growth. Confirmed observations of nutrient appropriation by
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knotweed demonstrates that the plant possesses specialized biology conducive to extreme
invasiveness (Walls, 2010). A study by Urgenson (2006) indicated that knotweed can
retain around 75% of its foliar nitrogen during seasonal senescence. By doing so, the
plant limits the amount of nitrogenous nutrients available to competitor species. This
aggressive tactic of reabsorbing its own nitrogen stores gives knotweed a significant
advantage over most other plants (Urgenson, 2006).
There has been increased attention brought to knotweed’s ability to exude
allelopathic phytochemicals as a mechanism to suppress competitive native vegetation
(Murrell et al., 2011; Vrchotová & Šerá, 2008; Bailey et al., 2009); although definitive
evidence of effective allelopathy by knotweed remains inconclusive. A controlled
greenhouse experiment by Murrell et al. (2011) tested the allelopathic potential of
Bohemian knotweed on six separate plant species (Roberts geranium [Geranium
robertianum]; spotted dead nettle [Lamium maculatum]; red campion [Silene dioica];
common comfrey [Symphytum officinalis]; perennial ryegrass [Lolium perenne]; and
rough bluegrass [Poa trivialis]) native to the study region. The results of this study
showed a significant indication of allelopathy by knotweed, though it was only effective
on the native forbs used in this experiment. The plants that grew in pots with knotweed
and absent of added activated carbon showed an average weight reduction of 57%, when
compared to pots without knotweed and activated carbon. Adding carbon to the pots
containing Bohemian knotweed and native plants provided a 35% reduction in the
suppressive effects of knotweed. The cutting of the knotweed shoots also had a profound
effect on all species in this study. For the single cutting treatment, biomass of knotweed
rhizome was reduced by 75% and biomass of the natives increased an equal amount. In

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the pots where knotweed was cut three times, knotweed rhizome biomass was reduced by
94% and native plant biomass increased by 177% (Murrell et al., 2011).
Knotweed can alter the composition of invertebrate taxa in areas where the plant
establishes a substantial presence (Claeson et al., 2014). Research shows knotweed may
support different assemblages of detritivores than native Pacific Northwest riparian plants
(Claeson et al., 2014). For example, Claeson et al. (2014) conducted a study in
Washington State which demonstrated that a variety of native aquatic invertebrate
detritivores prefer to feed on native leaf litter over knotweed. The results of this study
indicated that knotweed litter packs hosted considerably different invertebrate
assemblages than either the alder or cottonwood litter packs (Claeson et al., 2014).
Shredder invertebrate species, primarily stoneflies Zapada sp., Malenka sp., and Capnia
sp., were recorded in lower abundance in knotweed packs than on alder packs; “…these
results suggest that the influence of native species replacement by knotweed on stream
ecosystem function may be exacerbated by the loss of benthic invertebrate shredders”
(Claeson et al., 2014, p. 1540).
Gerber et al (2008) performed a similar study of invertebrate diversity in Swiss
knotweed infestations. The researchers in this project used pitfall and window traps to
collect indigenous invertebrates in native vegetation and Japanese knotweed infestations,
and then analyze the abundance, richness, and diversity of species (Figure 11). Through
the two-year duration of this study, the researchers documented around 40% less
invertebrate abundance collected in pitfall traps from knotweed infestations when
compared to native vegetation. The diversity of invertebrates was also affected by
knotweed presence, with fewer herbivorous invertebrates found in knotweed; predatory

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and detritivorous invertebrate reductions were less pronounced but still significantly
reduced. Furthermore, the researchers noted that morphospecies richness was 20% to
30% lower in knotweed plots than in native vegetation (Gerber et al., 2008).

Figure 11: Knotweed influences on the food web
There is an overall declining pattern of invertebrates, herbivores, predators, and detritivores in plots dominated by knotweed than by
native grasses or bushes in all three categories, total population, richness of morphospecies, and biomass.

Research studies such as the ones mentioned above indicate the severity of
knotweed alterations to the local biodiversity in areas of its substantial presence. The data
collected in these rigorous scientific projects contribute invaluable knowledge for Pacific
salmon habitat restoration; the goal of restoring this iconic species is contingent on
providing them with an environment that maintains native biodiversity and natural
ecological functions. The aggressive invader knotweed presents a substantial obstacle in
Pacific salmon habitat restoration efforts.

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4.1.3 Sediment Loads
Knotweed is well-known for its devastating ability to erode streambanks. Less
well known are the particular mechanisms by which these species degrade fluvial
geomorphology. Anecdotal accounts describe the dangers to streambank erosion by
knotweed and subsequent sedimentary deposition but fail to quantify the processes.
Researchers have acknowledged this gap and call for more research on the subject
(Lavoie, 2017). Thoroughly analyzing factors, such as the plant’s root cohesion value and
tensile strength, fine root material, as well as water pore pressure resistance, will lead to a
better understanding of knotweed’s effect on riparian zones and salmon habitat.
Much of the literature featured in this thesis suggest that the physical
characteristics of the plant may hold the key to understanding its erosional capabilities.
Several research studies allude to the rhizome network as a chief facilitator in knotweed’s
erosional rates. These species utilize a reproductive strategy primarily dependent on the
fragmentation of its rhizome structure rather than sexual propagation. “Rhizome
fragments have been found to sprout even when buried up to 1 [meter (around 3.3 feet)]
deep” (Seiger, 1993 as cited in Talmage & Kiviat, 2004, p. 5). These rhizomes are
relatively weak and are not suitable for binding sloped soil masses effectively
(Mummigatti, 2008).
When compared to many native tree species, knotweed has shallow underground
biomass which lacks substantial fine root material. Additionally, the seasonal growth
cycle of the invasive includes a complete die back of its aboveground biomass upon
exposure to freezing temperatures, leaving the local area unable to attenuate the erosional
effects of precipitation and stormwater runoff during winter months (personal

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communication with D. Ross as cited in Van Oorschot et al., 2017). In areas of knotweed
monoculture, there may be no available surface vegetation to dampen the effects of
extreme precipitation that accompanies Pacific Northwest winters.
In his 2003 doctoral dissertation, Richard Keim proposed that conifer species may
decrease the occurrence of erosion events in Pacific Northwest forests, not only by
anchoring the soil with deep extensive root systems, but also intercepting rainfall with
their dense wide canopies. He asserted that conifer forests may decrease soil saturation
and water pore pressure by, temporarily storing large volumes of water in their canopies,
and then slowly releasing that water over a prolonged duration (Keim, 2003). The results
of this study indicated that peak instantaneous rainfall intensities were diminished by
31% to 83% in old growth conifer stands (Keim, 2003). However, in the wintertime,
knotweed monocultures have negligible vegetation cover to intercept Pacific Northwest
rain. In fact, erosion rates in knotweed dominated areas remains consistently higher
during the fall-winter rainy season than in spring and summer (Arnold & Toran, 2018;
Van Oorschot et al., 2017; Urgenson, 2006).
Additional research needs to be conducted on knotweed and its impacts to
streambank erosion. A critical analysis of knotweed’s rhizome characteristics – primarily
belowground architecture, rhizome tensile strength, amount of fine material, and overall
cohesion value – may shed light on its inferior nature in stabilizing soil masses. By
methodically analyzing the physical and biological characteristics of the plant, science
may gain a clearer understanding of what unique mechanisms knotweed may employ that
exacerbate geomorphological riparian degradation. Any knowledge gained from such

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investigations would provide ecological conservationists with invaluable tools to apply to
Pacific salmon conservation efforts.

4.1.4 Stream Chemistry
Knotweed alters water chemistry by reducing biodiversity in the areas where it
proliferates. By suppressing native vegetation, knotweed reduces ecosystem services
provided by healthy riparian zones and negatively impacts water quality. Natural riparian
zones serve multiple functions in providing suitable habitat to Pacific salmon, including
filtering inflowing surface and groundwater, buffering streams from airborne pollutants,
and regulating nutrient cycling regimes (May et al., 1998; Everest & Reeves, 2007).
Monotypic stands of knotweed can reduce native plant abundance to negligible
levels, through out-competing, allelopathy, and nutrient appropriation. Riparian
conditions devoid of healthy vegetative layers, including tree canopies as well as
understory plants, may allow contaminants to enter a stream with minimal restrictions.
May et al. (1998) provided unequivocal evidence that adequate riparian buffer zones
around Pacific salmon habitat significantly improved the survival rate of the species. By
mitigating the effects of transitional pollutants in urbanized areas, healthy vegetated
riparian zones provide a substantial ecosystem service in the form contaminant
interception (May et al., 1998). Conversely, riparian areas lacking in adequate vegetation
can contribute to biological dysfunction and mortality of salmon populations. Knotweed
reduces native vegetation to critically low quantities if left uncontrolled. In winter
months, after complete dieback of surface material, monocultures of knotweed may leave
streambanks fully exposed to the inundation of chemical pollutants and toxic
contaminants.
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Additionally, Knotweed infestation can alter the nutrient cycling regime by its
unique ability to reabsorb the majority of its foliar nitrogen during seasonal senescence,
upwards of 70% (Figure 12) (Urgenson et al, 2009). This biologic function has a
profound effect on the success of the invasive as well as a considerable disadvantage for
all other proximal vegetation. Additionally, the minimal amount of nitrogen (N)
contained in knotweed leaf litter may contribute significantly less soluble N to streams.
By storing the nutrient reserves in its rhizome tissue, this plant can diminish available
nutrients to many important native vegetative species that provide a greater benefit to
Pacific salmon habitat (Urgenson et al, 2009). Knotweed essentially functions as a
nitrogen sink, slowly extracting nitrogen from the local environment as it efficiently
dominates the landscape. A European study by Parepa et al., (2019) found that Japanese
knotweed was more effective at nitrogen uptake when compared with five other plants
native to the geographic research area. The results of this study indicated that although
the knotweed demonstrated a similar rate of nutrient uptake to its native competitors, it
had a superior nitrogen-use efficiency (Parepa et al., 2019).

Figure 12: Knotweed N resorption prior to litterfall.
Leaf litter sapped from nutrients contributes less to the stream input of N (Urgenson et al, 2009, p. 1540).

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The research examples above allude to the biochemical nature of knotweed
species’ ability as a mechanism to alter the nutrient cycling regimes in areas of
proliferation. Similar research studies are recommended for the Pacific Northwest region,
in particular, to riparian areas that support populations of Pacific salmon. There also exist
substantial knowledge gaps regarding knotweed’s ability to alter several other water
quality parameters, such as pH, DO concentration, and pathogen transmission. Future
salmon conservation efforts would benefit greatly from further scientific investigation
into the processes by which knotweed alters chemical composition of aquatic ecosystems.

4.1.5 Water Flow Regimes
The potential effects that knotweed species may have on hydrologic processes
remains largely unexplored. The seasonal growth cycle of knotweed includes a complete
dieback of aboveground biomass soon after the first frost and provides no resistance to
water flow during that time. Anecdotal accounts claim that knotweed may obstruct
waterways when its stem material separates from the plant, floats downstream to an
accretion point, and concentrates in dense masses (McHugh, 2006). A few authors
speculate that knotweed may be the cause of increased flood risk (Cygan, 2018; Michigan
Department of Natural Resources [MIDNR], 2012), water flow reduction, and stream
obstruction (Lavoie, 2017; McHugh, 2006), but the extensive literature review contained
in this project did not uncover substantial quantifiable data on the subject.

4.1.6 Stream Temperatures
One prominent characteristic of knotweed infestation is a decrease in riparian
canopy cover as a result of native tree suppression. This could arguably be considered
this invasive plant’s most harmful effect on salmon habitat since reductions in canopy
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cover equate to an increased amount of solar radiation able to reach the water’s surface.
Healthy native riparian forests exert a strong control on stream microclimates by
absorbing the sunlight during photosynthesis. Knotweed does not possess an adequate
foliar canopy to intercept a significant amount of solar radiation at any point during its
growth cycle (Harbaugh, 2017). Substantial riparian vegetation also has a temperature
control function on streams during the cold season, when it acts as an insulating layer and
prevents radiant cooling of the water; thereby keeping water warmer than outlying
temperatures (Everest & Reeves, 2007). Knotweed simply does not possess the physical
structure necessary to regulate the temperature of riparian environments. The literature
cited indicates that any negligible effect this invasive plant may have on blocking solar
radiation or insulating stream water approaches the values associated with bare ground.
Therefore, knotweed must be considered as an aggravating factor in high temperature
stream conditions that are extremely detrimental to Pacific salmon habitat.

4.1.7 Shelter Abundance (Woody Debris)
Knotweed also limits woody debris recruitment into riverscapes, negatively
impacting Pacific salmon habitat. By suppressing the establishment, growth, and
development of large native tree species, knotweed renders large areas of riverine
environments completely absent of DWD components. Since juvenile salmon rely so
heavily on DWD for their survival, this aspect of knotweed ecology should be considered
a high priority reason for mitigation and control of large infestations that occur around
salmon bearing streams. The 2011 Chehalis Basin Salmon Habitat Restoration and
Preservation Strategy for WRIA 22 and 23 considers inclusion of DWD a necessity for
effective salmon habitat restoration and mentions it a total of 387 separate times
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throughout the body of the document; coincidentally, all four of these knotweed species
found in Western Washington are listed as invasive plants of concern for the
implementation of that project. Since knotweed has a highly effective competitive ability
to displace native tree species in riparian ecosystems, it must be considered a major threat
to juvenile Pacific salmon.

4.1.8 Migration Route Obstruction
Knotweed can also cause blockages in waterways and obstruct the migration route
of Pacific salmon. While the research for this project did not discover substantial
quantitative data on the occurrence of knotweed related waterway obstruction, previous
studies have indicated that the canes of this plant, when detached from their base, can be
transported by flowing water as well as collect in tangled masses (McHugh, 2006).
Hypothetically, any obstruction in a stream channel can accrete additional material and
further increase the blockage; careful measurement of these occurrences was not
uncovered in the literature reviewed.
Any significant knotweed related occurrence of salmon migration route
obstruction most likely originates from the invasive plant’s ability to induce streambank
erosion (Figure 13), an impact also explained previously in Chapter 4.1.3. Arnold and
Toran (2018) asserted that the greatest risk of knotweed erosion occurs in areas of
streambank that have been incised during periods of high discharge. Over their 9.5-month
observation of knotweed infested streambanks, the researchers measured averages of 29
centimeters (~ 11 inches) of erosion on incised banks and nine centimeters (~ 3.5 inches)
of erosion on banks with little incision (Arnold &Toran, 2018).

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Figure 13: [photo] Knotweed-induced erosion
This is an image of a Japanese knotweed infestation and a streambank slump
(photograph by Jenn Grieser, New York City Department of Environmental Protection, Bugwood.org).
This image was cited as specified by the author.

These observations have implications for the plants’ ability to trigger large soil
mass displacement into salmon bearing waterways. Arnold and Toran’s (2018) work
suggest that knotweed induced erosion is more pronounced in streambanks that have a
sharp vertical slope gradient or project horizontally over a waterbody than those with a
gradual slope gradient. The modern universal soil loss equation, commonly used by
geoscientists, considers the slope length factor and slope steepness factor in the overall
prediction of soil loss quantity in a given area.

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A= (R)(K)(L)(S)(C)(P)
Where: A is mean annual soil loss (metric tons per hectare per
year), R is the rainfall and runoff factor or rainfall erosivity
factor (megajoule millimetres per hectare per hour per year),
K1 is the soil erodibility factor (metric ton hours per megajoules
per millimetre), L is the slope length factor (unitless),
S is the slope steepness factor (unitless), C is the cover and
management factor (unitless), and P is the support practice
factor. (Benavidez et al., 2018)
This equation expresses the probability of a greater volume of mass-wasting occurring
with steeper slopes than with gentle slopes of the same length (Benavidez et al., 2018).
Incised streambanks containing knotweed infestations can instantaneously deposit large
volumes of material during the event of streambank collapse and possibly block passage
of migrating Pacific salmon.

4.1.9 Predator Habitat
The literature reviewed for this thesis was insufficient on the topic of knotweed’s
influence on salmon predation. It is possible that a gap in scientific literature exists,
warranting future research, or that because knotweed grows alongside water rather than
within it, any possible predator habitat would be more terrestrial rather than aquatic in
nature.

4.2 Reed canarygrass (Phalaris arundinacea)
Is reed canarygrass (P. arundinacea) native to Western Washington? Native
populations of reed canarygrass may have hybridized with multiple European genotypes
and thus they have become indistinguishable (Lavergne & Molofsky, 2007). As stated in
Chapter 4.2.1, there have been Phalaris specimens collections by David Douglas, David
Lyall, and others from before 1860 which are considered to be the native North American
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grass; however, the native genotype seems morphologically identical to the invasive
European population (Hitchcock & Conquist, 2018). For the purpose of this thesis and
because there is no good way to discern between the two, it will be assumed that all reed
canarygrass in Washington State is the invasive European genotype.
A large rhizomatous wetland perennial, reed canarygrass, has been designated a
class C noxious weed in Washington due to its tendency to dominate wetland areas,
negatively impact local ecology, and alter hydrologic processes. In temperate regions,
growth of reed canarygrass begins early in the spring, senescence occurs with summer
drought, and limited vegetative growth resumes in autumn with increased precipitation
(Stannard & Crowder, 2003). This cool-season C3 grass possesses sturdy rigid stems
about 1 centimeter (less than half an inch) in diameter with a reddish hue at the top
during the growing season (Seebacher, 2008) (Figures 13 & 14). Reaching an average
mature height of 1 to 2 meters (~ 3 - 6.5 feet) tall, it produces dense crowns and extensive
underground rhizome networks. This invasive propagates both by vigorous seed dispersal
and rhizomatic regeneration (Barnes, 1999; Kim et al., 2006), as well as stem
fragmentation (Wisconsin Reed Canary Grass Management Working Group
[WRCGMWG], 2009).
Reed canarygrass has a considerable tolerance for environmental stress, such as
cold temperatures, (Seebacher, 2008), hydrologic inundation, and anoxic soil conditions
(Martinez, 2013; Lavergne & Molofsky, 2004) but less of a tolerance to shade (Kim et
al., 2006). Reed canarygrass commonly forms highly productive monotypic stands that
negatively impact many wetland ecosystems throughout Washington State (NWCB,
1995). This invasive grass has been documented to slow water velocities, increase

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sediment deposition rates, and affect local flood regimes in areas which it dominates
(Seebacher, 2008). In fact, this ubiquitous species causes such significant damage that
David Heimer with the Washington Department of Fish and Wildlife (WDFW) has
cleverly deemed it the “plastic grocery bag of the weed world” (D. Heimer, personal
communication, February 10, 2021). However, shade could be a limiting factor in its
growth potential. Kim et al. examined multiple studies that indicated how reed
canarygrass’ above ground biomass was not only stunted by 97% in shaded greenhouse
experiments, but new seedlings did not show germination in the dark environments until
a disturbance allowed a gap of light to penetrate through the canopy (Kim et al., 2006).
Reed canarygrass ranked the second highest in the survey results, with 47% of
respondents mentioning this species as having a high impact on freshwater ecosystems.
When asked why this plant was specifically a priority, respondents mentioned that reed
canarygrass:
1) outcompetes other vegetative species (71% of reed canarygrass respondents),
2) is highly aggressive and spreads easily (71%),
3) is ubiquitous in both streams and upland areas (57%),
4) can be difficult to manage (57%),
5) chokes out freshwater systems (57%),
6) alters stream morphology (43%),
7) reduces available salmon habitat (14%),
8) reduces passageways for salmon (14%),
9) increases water temperatures (14%), and
10) creates dense matting (14%).

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The survey responses indicated that reed canarygrass can quickly dominate an area,
changing stream morphology, and reduces the survivability of Pacific salmon.

Figure 14: [photo] Reed canarygrass identification drawing
Drawing to identify reed canarygrass (1University of Florida Center for Aquatic and Invasive Plants, 2001).
Cited with authors permission.

Figure 15: [photo] Reed canarygrass identifying photos
Photograph used to help identify reed canarygrass features (Michael D. C. & Daniel J. U., 2019).

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4.2.1 Dichotomy
The following dichotomy is taken directly from the second edition of the Flora of
the Pacific Northwest (2018), in which the genus Phalaris begin on page 809 (Hitchcock
& Conquist, 2018).
Phalaris (p. 809)
Spikelets in congested, often spikelike panicles, articulated above the glumes,
occasionally spikelets deciduous as a whole, strongly compressed, (1-)3 flowered,
the uppermost floret generally perfect, the lower one(s) represented by a sterile,
generally hairy, more or less linear lemmas, or lacking; glumes approximately
equal, greatly compressed, often strongly keeled, generally 3-nerved; fertile
lemma generally hardened, mostly appressed-hairy, rounded to acute, much lower
than the glumes; stamens 3; annual or perennial with hollow culms, open sheaths,
membranous ligules, and flat blades rolled in the bud.
1a. Plants long-rhizomatous, perennial; glumes broadest near base, lanceolate, the
keels not winged, or wings less than or equal to 0.2 millimeters wide;
inflorescence an elongate more or less oblong to lanceolate panicle, generally
slightly lobed at base, with numerous ascending to spreading branches visible in
flower, appressed in fruit; fertile lemma shiny; marshes, shores, swales, wet
meadows, ditches, disturbed ground; collections by David Douglas (east Cascades
along Columbia River), David Lyall (Washington Cascades), and others from
before 1860 are apparently the native North American race, but inseparable
morphologically from the invasive European introduced race in our area used for
rangeland improvement by around 1885; Alaska southward, both sides Cascades,
to California, east to Atlantic coast; reed canarygrass
1. P.
arundinacea L.

4.2.2 Overall Biodiversity (Flora, Fauna, Invertebrates)
Many scientific studies have shown that reed canarygrass can reduce the
abundance and diversity of local plant and invertebrate assemblages (Green &
Galatowitsch, 2002; Lavergne & Molofsky, 2004; Spyreas et al., 2010). Several
biological and evolutionary traits converge to provide this plant with advantages over
competitors. Miller and Zedler (2003) indicated that reed canarygrass possesses a high
degree of architectural plasticity when grown in high competition settings. This enables
reed canarygrass to allocate nutrients to increase canopy volume, by altering its root
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length to biomass ratios, effectively shading out its competitors (Miller & Zedler, 2003).
Coops et al. (1996) discovered that this grass has the ability to transfer nutrients from its
roots to its shoots during periods of inundation, and from its shoots to its roots during
drought, presumably developed as an evolutionary water management adaptation. In
addition, when in proximity to competitors, reed canarygrass can preferentially distribute
nutrients to increase its shoot length which intercepts sunlight more effectively than
neighboring plants (Lavergne & Molofsky, 2004).
Tamura & Moriyama (2001) found that reed canarygrass is better equipped to
survive harsh winters and may also have a stronger growth response in the early spring
than other plant species. The authors performed a controlled experiment to study the
nutrient storage capacity of reed canarygrass, orchard grass, timothy, and ryegrass roots
during late summer to early spring (Tamura & Moriyama, 2001). After sampling the
plants, once in November and once in March, the researchers measured the aboveground
and belowground growth, then conducted high-performance liquid chromatography
analysis on the foliage and root tissues (Tamura & Moriyama, 2001). The non-structural
carbohydrates in the reed canarygrass roots were found to be three times higher than in its
foliage, and significantly higher than any of the other plants in the study (Tamura &
Moriyama, 2001). This early spring ‘jump-start’ could prove to be especially
advantageous in the cold dark winters of the Pacific Northwest.
This domineering species has the strong propensity to exclude all other plant
species from within areas it infests. A 2013 report for the U.S. Army Corps of Engineers,
stated that reed canarygrass was the most prolific non-native plant found in the main stem
Columbia River estuary, accounting for approximately 28% total cover of all vegetative

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species present (Diefenderfer et al., 2013). Spyreas et al. (2010) investigated the impacts
on wetland ecosystems associated with reed canarygrass invasions and found that there
existed a negative correlation between the plant’s density and local biological integrity
(Spyreas et al., 2010). They uncovered a diminishing effect of the invasive grass on
multiple taxa, including plants, small mammals, birds, and arthropods (Spyreas et al.,
2010).
Reed canarygrass has a strong positive growth response to eutrophic soils and
when exposed to agricultural runoff it can surpass the development of most other native
plant species. Green and Galatowitsch (2002) performed a field experiment using
controlled quantities of a common form of agricultural fertilizer (NO3-N) in sedge
meadows with occurrence of reed canarygrass. Native vegetation, primarily meadow
sedge species, consistently demonstrated reduced growth rates when in proximity of reed
canarygrass. This study indicated that, with the application of the fertilizer, the native
sedges showed a growth reduction by as much as 50% (Green & Galatowitsch, 2002).
Klopfenstein (2016) conducted a study on the effects that reed canarygrass had on
Pacific salmon habitat within the Columbia River estuary and found that the plant altered
the composition of macroinvertebrate populations in areas of dense proliferation. Her
research indicated reduced growth and development among juvenile salmon when
confined to areas dominated by reed canarygrass. Klopfenstein insisted that this occurred
as a result of a decrease in certain energy-rich invertebrate species that are supported by
more diversely vegetated ecosystems, rather than the common assumption of a
diminished abundance in invertebrate prey resources in response to invasive plant
presence (Klopfenstein, 2016); as previously illustrated in Figure 8.

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Reed canarygrass does support some native organisms in the Pacific Northwest.
Holzer and Lawler (2015) conducted a study of native frog species of Oregon within 62
separate ponds, with varying densities of reed canarygrass, and the ecological benefits
provided to the amphibians by the invasive grass. By taking an inventory of vegetation
and amphibian populations within the ponds during summer months, the researchers
determined that reed canarygrass hosted greater abundances of Pacific chorus frogs
(Pseudacris regilla) than any other vegetation in the study area (Holzer & Lawler, 2015).
The ponds that had an occurrence of reed canarygrass contained an average of five times
the number of adult male Pacific frogs than ponds with other vegetation. Out of the 386
separate frog egg masses observed, 205 of them had been laid in ponds with reed
canarygrass (Holzer & Lawler, 2015). Tadpoles showed a strong positive statistical
correlation to reed canarygrass presence as well (Holzer & Lawler, 2015). The
researchers also noted that approximately ten percent of the ponds surveyed contained
four separate native amphibian species, including two frog species and two salamander
species (Holzer & Lawler, 2015).
Reed canarygrass provided Pacific chorus frogs with conditions beneficial to its
development and survival (Holzer & Lawler, 2015), by doing so it may also negatively
impact any Pacific salmon which coincide with populations of the frog. Since salmon do
not regularly choose to feed on amphibians (Richter & Azous, 1995), the contributions of
these frogs to salmon habitat may be negligible. On the other hand, Pacific chorus frogs
and salmon species may be competing for the same prey resources within their mutual
range. Pacific chorus frogs have been documented with arachnids, such as those in the
order Araneae in both female and male stomachs; insects in the order Coleoptera in both

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male and female stomachs, the Diptera, Hemiptera, and Hymenoptera order in male
stomachs; the moth/butterfly order of Lepidoptera in female stomachs; and the woodlice
order of Isopoda in both female and male stomachs (Hothem et al., 2009). Many of the
invertebrate species mentioned above are also commonly preyed upon by Pacific salmon
in Western Washington (Dillon, 2020).

4.2.3 Sediment Loads
Available scientific literature on reed canarygrass does not point to a direct
relationship between this plant and streambank erosion. Conversely, it acts much like a
natural sediment trap, building up the elevation in the areas it proliferates. Martinez
(2013), performed an extensive analysis on the geomorphic effects of reed canarygrass on
a Pacific Northwest river and determined that the invasive possessed high root cohesion
values which indicated it as a suitable streambank stabilizing species (Martinez, 2013).
Additionally, the tendency of reed canarygrass to form dense mats of above ground
biomass may protect streambanks from erosional effects of high-water flow and scouring.
In fact, the invasive plant’s ability to build up layers of sediment may be so effective that
it can clog waterways, potentially decreasing side channels accessible to salmon (Silver
& Eyestone, 2012).

4.2.4 Stream Chemistry
Since reed canarygrass commonly dominates areas of intense stormwater runoff
(Galatowitsch et al., 2000), it is presumed to have some effect on the chemistry flowing
into the water body it encompasses. Although evaluations of this plant’s ability to
intercept toxic stormwater runoff or aerosol pollutants has not been thoroughly discussed
by any of the literature discovered in this project, it may be inferred that reed canarygrass
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monocultures do not possess the physical attributes, such as those of native Pacific
Northwest riparian forests, necessary to mitigate significant quantities of common stream
contaminants. Pacific Northwest riparian integrity is characterized by wide buffers of
mature conifer forests and well-developed morphologically complex floodplains (May et
al., 1997).
Reed canarygrass can simplify the biological diversity of riparian zones and
floodplains by forming dense monotypic stands along vast stretches of streambanks.
Since this invasive grass grows to an average maximum height of two meters (~ 6.5 feet),
it can be considered inferior, in its ability to intercept high elevation aerosol drift, to
many of the large Pacific Northwest tree species which grow to heights in excess of 20 to
30 meters (~ 65 - 98 feet), respectively. Additionally, the grass’ tendency to act as a
sediment trap may impair the water filtration value of an area by reducing the soil
percolation rate; thereby, limiting the subsurface water flow; though, studies on the
subject remain inconclusive.
Quantitative data suggests that reed canarygrass may provide some value in
removing heavy metal contamination (Marchand et al., 2014; Moschner et al., 2020). C.
R. Owen (1999) used a piezometer, a device used to measure electrical conductivity of
water, to determine that reed canarygrass dominated wetlands within the study area
maintained higher average specific conductance’s when compared to the other twelve
vegetation dominated sites assessed. Future research on reed canarygrass’ efficacy to
intercept toxic compounds, pollutants, and agricultural chemicals should be conducted to
gain a better understanding of its ecological impacts, specifically on Pacific salmon
habitat.

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This aggressive wetland plant has been documented to decrease DO concentration
in streams that it envelops. By outcompeting native riparian plants and forming dense
aboveground biomass, reed canarygrass can change the local hydrology so significantly
that water quality is drastically reduced. Reed canarygrass can restrict water flow to the
degree that it may absorb a greater to amount of solar radiation than if it were flowing at
faster rates. This increase in water temperature negatively affects the solubility of DO and
adversely impacts the survivability of salmonid species.
Questions remain about whether reed canarygrass contributes organic material to
the environment that may be considered toxic to aquatic organisms. Due to the fact that
reed canarygrass contains naturally high levels of several alkaloid compounds (Coulman
et al., 1977; Østrem, 1987), it may have the potential to impact salmon species or their
prey resources by chemical contamination. Further research into the effects of these
alkaloids, primarily Phenols, Indoles, and β-carbolines, on Pacific salmon habitat should
be conducted.
Although reed canarygrass has been successfully utilized in phytoremediation for
extremely toxic environmental conditions, such as sewage sludge spills (Antonkiewicz et
al., 2016; Rosikon et al., 2015), mining operations (Moschner et al., 2020), and industrial
manufacturing sites (Chekol et al., 2002), its capacity for long-term phytoremediation
remains inconclusive. Rosikon et al. (2015) compared the heavy metal (Cd, Ni, and Zn)
contaminant removal by reed canarygrass and giant miscanthus from given inputs of
municipal or industrial sewer sludge (Rosikon et al., 2015). After two years of study and
analysis, the researchers concluded that reed canarygrass could provide effective removal
of Zn and Ni during the initial growing season, with Zn retention considerably higher in

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the biomass of reed canarygrass when compared with miscanthus (Rosikon et al., 2015).
Soil amendments did provide some significant increase in the absorption rate of heavy
metals by reed canarygrass when compared to the control samples during the second year
of the study, but this ability was significantly diminished compared to the first growing
season; reed canarygrass showed little capacity to remove Cd in any of the experiments
(Rosikon et al., 2015). Timing and the type of contaminant thus appear to be key factors
in the phytoremediation capabilities of reed canarygrass.
Still, reed canarygrass can be effective in obscure applications of
phytoremediation. An experiment by Moschner et al. (2020) shows that reed canarygrass
can be used as an effective ‘phytomining’ method to extract precious metals from
contaminated soils, though the researchers indicated that this wetland grass was most
effective when provided with regular inputs of soil amendments or compost (Moschner et
al., 2020). These researchers concluded that reed canarygrass could successfully extract
Mn, Fe, Zn, As, Pb, Cd, and rare earth elements when provided with soil amendments
(Moschner et al., 2020). This wetland perennial grass has even been confirmed to
successfully mitigate the toxic effects of soil contamination by the widely used mining
explosive trinitrotoluene (Chekol et al., 2002).
Although the examples provided in the studies referenced above indicate that reed
canarygrass can be an effective phytoremediator in moderately to severely contaminated
sites, studies focusing on the ability of this invasive plant to remove low levels of toxins
common to riparian zones in Pacific salmon habitat remain underrepresented in scientific
literature. Since Pacific salmon habitat must maintain high environmental quality
standards, it may never reach a level of toxicity at which reed canarygrass could provide

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substantial detoxifying effects. Questions about the efficacy of reed canarygrass to extract
low levels of environmental pollutants, chemical wastes, and toxic compounds may only
be resolved by thorough investigation and scientific analysis.

4.2.5 Water Flow Regimes
Due to a combination of its physical characteristics, such as the high density of
above ground material, stiff stems, and large foliar surface area, reed canarygrass can
mechanically obstruct water flow to the point that it negatively impacts local ecology
(Martinez, 2013). Gebauer et al. (2015), Owen (1999), and Schilling and Kiniry (2007)
discussed the severe water loss associated with this invasive grass, but few have
submitted quantifiable data or described the processes by which water loss occurs. It is
widely accepted that reed canarygrass performs as a wetland sediment trap, has the
tendency to partition water flow, and in extreme cases, even forms stagnant pools of
isolated water. A combination of specialized biology and unique architecture enable this
plant to drastically alter the hydro-morphology of a local area (Owen, 1999). In
monotypic stands of reed canarygrass within floodplains, these biological traits can
enable a positive feedback loop of reduced flow followed by sediment deposition and
plant growth (Seebacher, 2008).
Previous studies have looked at the transpiration rates of reed canarygrass as a
mechanism by which this plant may limit water availability (Gebauer et al., 2015;
Schilling & Kiniry, 2007). A 2015 study on Eastern Washington wetlands infested with
reed canarygrass provided detailed data that suggests this aggressive plant can greatly
diminish water resources by foliar transpiration (Gebauer et al., 2015). By measuring leaf
area transpiration with a Li-Cor® portable photosynthesis system, the researchers
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assessed the water use of several wetland species in the project area (Gebauer et al.,
2015). They revealed that in the active main channel bank and floodplain the
transpiration rate of reed canarygrass was many times greater than all of the other plants
studied, except one. It was suggested that this high transpiration rate was likely due to
reed canarygrass having three times the total average evaporative surface area per square
meter of ground surface compared to other vegetation in the study (Gebauer et al., 2015).
The measurements of reed canarygrass transpiration rate, based on mean leaf area, were
not significantly different from other plants; yet, when the cumulative transpiration rate
of its total canopy was measured, it surpassed all others. The researchers concluded that,
because of its high transpiration rates, reed canarygrass may play a significant role in
regional water loss within wetland ecosystems (Gebauer et al., 2015).
A 2007 project by Schilling and Kiniry attempted to quantify the average water
use by reed canarygrass in an Iowa wetland ecosystem. By relying on proven predictive
models for plant transpiration rates based on leaf area index, light absorption and
photosynthesis, as well as biomass production among other parameters, Schilling and
Kiniry were able to simulate the estimated water use of reed canarygrass (2007). The
results of this study elucidated several insightful characteristics of this wetland invader.
The researchers noted that nocturnal water use by reed canarygrass decline precipitously
from daytime levels (Schilling & Kiniry, 2007). Furthermore, the grass’ water
consumption was relatively consistent from the months of May through September, but
water use after October was nearly imperceptible (Schilling & Kiniry, 2007). Reed
canarygrass had the greatest daily water table extraction rate during the month of July at
around 3.3 millimeters (0.1 inch), May through September averaged 2.3 to 2.8

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millimeters (Schilling & Kiniry, 2007). This study could be replicated, with a few
adaptations for Pacific Northwest conditions, to determine reed canarygrass’ water use
effects on Pacific salmon habitat.

4.2.6 Stream Temperatures
Reed canarygrass can increase stream temperatures of a local area by impeding
water flow, thereby extending the duration of solar radiation exposure to the water’s
surface. This prolonged exposure increases water temperature and evapotranspiration,
and as a result, initiates a positive feedback loop of warming water temperatures,
increasing rate of evaporation, and reduced water volume. These processes create a
convergence of inhospitable environmental conditions for Pacific salmon species. Not
only does this prolific wetland grass raise water temperatures to the point at which it may
inhibit the biological function of salmon, but it also diminishes aqueous DO
concentrations and reduces the volume of water available.

4.2.7 Shelter Abundance (Woody Debris)
Because reed canarygrass can reduce native tree species abundance in riparian
areas, it can limit woody debris recruitment to aquatic environments. By forming dense
monotypic stands over large areas, this invasive wetland perennial can establish
sprawling ‘grass deserts’, devoid of substantial biodiversity. Reed canarygrass commonly
covers 50% to 100% of invaded habitats in Washington (Lavergne & Molofsky, 2004).
Furthermore, the physical structure of this invasive does not provide any substantial
material which could serve as in-stream shelter for juvenile salmonids, as does DWD
(Seebacher, 2008).

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4.2.8 Migration Route Obstruction
Several features of reed canarygrass enable it to drastically alter channel
morphology and stream embankments. Formation of dense impenetrable mats is a
defining characteristic of this successful invader; few native plant species can produce
such highly concentrated biomass as reed canarygrass. Vast quantities of sediment can
then accumulate and increase the elevation directly below stands of the invasive. One
year’s sediment deposition becomes the growth substrate of reed canarygrass in the
subsequent year. The cycle can perpetuate to the point of complete stream channel
obstruction during part of the year, typically in late-summer and early fall (Seebacher,
2008). For example, in the Quinault River basin reed canarygrass remains a major
concern of off-channel access for juvenile salmon (Silver & Eyestone, 2012). The
Columbia River estuary contains a considerable presence of this high-risk grass
(Diefenderfer et al., 2013), and it may pose a substantial threat to homing salmon
populations. For these reasons, reed canarygrass must be considered harmful to salmon; it
limits access to off-channel habitat and can totally obstruct passage routes.

4.2.9 Predator Habitat
Northern pike (Esox lucius) is a carnivorous fish with a voracious appetite known
to prefer salmonid species (Carim et al., 2019) (Figure 16). This predator is also
considered an invasive species in Washington (Washington Invasive Species Council
[WISC], 2020) and has been documented in parts of the Columbia River (Carim et al.,
2019) as well as other Eastern Washington rivers (WISC, 2020). In Wisconsin, Northern
pike is an actively managed native species (Wisconsin Department of Natural Resources,
n.d.). A 1977 technical bulletin for the Wisconsin Department of Natural Resources
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advocated for the dispersal of reed canarygrass seeds in marshes that were devoid of
grasses in an effort to maintain northern pike habitat (Fago, 1977). Due to the age of this
report, the reed canarygrass discussed was most likely a native genotype and not the
invasive form that also currently plagues Wisconsin. However, if northern pike receives
habitat benefits from reed canarygrass, then it will be beneficial to remove this grass from
salmon habitat in order to better protect Western Washington’s declining salmon
population from such an aggressive invader.

Figure 16: [photo] Northern pike stomach contents
An image of northern pike stomach contents full of juvenile salmon (photo by Kristine Dunker).

4.3 Yellow flag iris (Iris pseudacorus)
Designated a class C noxious weed in Washington State, yellow flag iris (Iris
pseudacorus) is easily distinguished by its vibrant yellow coloration with three upward
pointing petals and three larger hanging sepals which are often streaked with brown or
purple venation (Figures 17 - 19). Yellow flag iris is native to Eurasia (Morgan et al.,
2018; Sutherland, 1990). Reaching an average mature height of 1.5 meters (5 feet), this
invasive perennial flower is commonly found in wetlands throughout the temperate
regions of the world (Sutherland, 1990). Single or multiple flowers with a diameter
between 8 to 10 centimeters (3 - 4 inches) can form from seed pods attached to long
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round stems and surrounded by long blade-like leaves (Sutherland, 1990). This prolific
invasive plant reproduces effectively by sexual and vegetative means, such as by seeds or
clonally (Sutherland, 1990). Yellow flag iris develops seeds 6 to 7 millimeters (around a
quarter of an inch) in diameter in three-sided capsulate pods around 3.5 to 8.5 centimeters
(1.4 to 3.3 inches) long (Morgan et al., 2018). The rhizomes are 1 to 4 centimeters (0.4 1.5 inches) in diameter, up to 30 centimeters long (11.8 inches), prefer saturated
substrate, and can withstand acidic soil conditions, pH around 3.6 (Sutherland, 1990;
Yousefi & Mohseni-Bandpei, 2010).
Due to a substantial lack of literature describing this invasive plant’s ecological
effects in the Pacific Northwest, accumulation of relevant data has been fraught with
difficulty. Many publications express field observations of yellow flag iris but do little to
quantify its effects on cooccurring organisms. Speculations on the harms this aggressive
wetland plant may have on Pacific salmon abound, yet most studies on the subject remain
inconclusive. There exists a significant knowledge gap of how yellow flag iris impacts
water quality standards, such as flow, chemistry, and turbidity. The effects this plant has
on native biodiversity has not been adequately documented, and its impacts to salmon
habitat require extensive future investigation. The following sections will attempt to form
correlations between existing yellow flag iris data and Pacific Salmon habitat.
Yellow flag iris ranked the third out of the top four species from the survey
results, with 33% of respondents mentioning this species as having a high impact as an
invasive on freshwater ecosystems. When asked why this plant was specifically a
priority, respondents mentioned that yellow flag iris:
1) is very widespread (60% of yellow flag iris respondents),

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2) easily outcompetes other vegetation (40%),
3) lacks sufficient management (40%),
4) proliferates aggressively (40%),
5) changes hydrology (20%),
6) difficult to control (20%), and
7) the seeds have a high germination rate (20%).
The survey responses speak to the difficulty in managing such a prolific species.

Figure 17: [photo] yellow flag iris flower
Yellow flag iris flower photograph by Jonathan Billinger (Jonathan B., 2019).

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Figure 18: [photo] Yellow flag iris identification drawing
Drawing to identify yellow flag iris (2University of Florida Center for Aquatic and Invasive Plants, 2001).
Cited with authors permission.

Figure 19: [photo] Yellow flag iris proliferation
Yellow flag iris displaying its ability to form monocultures in a seasonal stream area. Photo taken by Jennifer Petrie (Jennifer P.,
2020).

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4.3.1 Dichotomy
The following dichotomy is taken directly from the second edition of the Flora of
the Pacific Northwest (2018), in which the genus Iris begin on page 695 (Hitchcock &
Conquist, 2018).
Iris (p. 695)
Flowers 1-several, subtended by paired leaf like spathes; perianth segments fused
at base, forming a short to much-elongate, slender to more or less flaring tube;
sepals (the outer 3 segments) showy, spreading to reflexed, strongly pencilled
with brown to purple and with a thickened ridge or line of hairs near the base
(signal); petals generally ascending to erect, generally narrower than the sepals;
stamens opposite the sepals; style branches opposite the sepals and generally
curved over them and concealing the stamens, generally petaloid, with 2 terminal
lobes (crests), the stigma generally a short flap projecting on the lower side at
base of the crests; capsule fusiform to subglobose, generally coriaceous; ours
rhizomatous herbs with linear, generally flattened, chiefly basal leaves and leafy
to naked flower stems.
1a. Widest leaves 2-6 centimeters wide; rhizomes 1.2-3 centimeters wide; stems
6-15 decimeters
2b. Sepals glabrous; seeds 6-10 millimeters
3b. Seeds dull brown, flattened; flowers bright yellow; leaves
deciduous, grass-green to light green, not foul-smelling when
crushed; wet areas to shallow water around lakes, ponds, ditches,
and stream banks; invasive European intro; British Columbia
southward, both sides Cascades, to California, eastward across
most of North America; yellow forms or i. [“i.” is not defined;
assumed to mean irises]
3 I. pseudacorus L.

4.3.2 Overall Biodiversity (Flora, Fauna, Invertebrates)
Much like several of the invasive vegetative species mentioned in this project,
yellow flag iris has been shown to from dense proliferations in the areas it dominates.
This can result in a drastic reduction in floristic complexity of aquatic ecosystem which
may diminish natural functions in wetland environments (Jacobs et al., 2010). Several

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biological and physical characteristics of this invasive plant may provide it with an
effective arsenal of adaptations to outcompete native species in infested areas.
The high tolerance to environmental stress may give yellow flag iris a foothold in
settings where local conditions are less suitable to its native counterparts. Research has
been shown that yellow flag iris can withstand freezing temperatures, acidic soils, and
brackish waters (Fagerstedt, 1988; Simon, 2008; Sutherland, 1990). Additionally, this
wetland invader can tolerate sustained periods of full submersion in water without
suffering irreparable damage (Jacobs et al., 2010; Hetherington et al., 1983).
Furthermore, yellow flag iris is considerably tolerant of drought, and has been observed
growing three months during the absence of water (Sutherland, 1990). The large
carbohydrate storage potential within this plant’s rhizome, upwards of 80% total weight,
may give it the ability to persevere through stressful conditions (Hanhijarvi and
Fagerstedt, 1994 as cited in Tarasoff et al., 2016).
In his doctoral thesis for the University of St. Andrews, Scotland, Fagerstedt
(1988) detailed his study on the anoxic tolerance of three barley cultivars in comparison
to yellow flag iris. The author conducted several lab experiments which subjected the
four plant species to prolonged periods of anoxia, then analyzed the biochemical changes
that occurred in their tissues (Fagerstedt, 1988). The results of this study indicated that
yellow flag iris possessed a far greater resistance to anoxic stress than the barley species
(Fagerstedt, 1988). By producing high quantities of a plant enzyme (superoxide
dismutase), during and after anoxia, yellow flag iris was able to negate any potential
oxidative damage its tissues would have incurred upon reintroduction to aerobic
conditions; “It can be seen that the extraordinarily high anoxic [superoxide dismutase]

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SOD activity in rhizomes of I. pseudacorus in comparison to that of barley and rice, is
correlated with the ability to survive prolonged anoxia…” (Fagerstedt, 1988 pg. 123).
This adaptive biochemical ability, in addition to the possession of well-developed air
sacks in their rhizomes (aerenchyma), provide yellow flag iris with an exceptional
tolerance for natural flooding conditions which most plant species are ill-equipped to
cope with (Fagerstedt, 1988).
Mopper et al. (2016) performed a common garden experiment which studied the
effects of competition between yellow flag iris and a native Southern U.S. iris species (I.
hexagona) when subjected to a series of salinity treatments. The researchers measured the
growth of each plant and then applied the collected data to a predictive statistical model
in order to evaluate the long-term probability of domination in a natural setting for each
iris species. The yellow flag iris plants appeared to be unaffected by the intra- and
interspecific competition, but the native iris showed significantly diminished growth
when grown together with yellow flag iris (Mopper et al., 2016). The researchers noted
that in some of the pots containing both species, the native iris was literally pushed out of
the substrate by the aggressive growth of the invasive (Mopper et al., 2016). The data
collected from the salinity treatments and the competition experiment, when entered into
a computer simulated model, predicted that yellow flag iris would eventually exclude the
native iris in freshwater wetlands, but the native plant was predicted to dominate in saline
or brackish environments (Mopper et al., 2016).
Invasive vegetative species do not always limit abundance, biodiversity, richness
of all native organisms in the areas which it dominates. In some circumstances, invasive
plants may demonstrate a strong supportive function to the survival of certain species of

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flora, fauna, or microbes (Sagoff, 2009). In other instances, non-native plants may have
no impact, positive or negative, on native species. Forecasting the potential impact of an
invasive species to an introduced range often fails to approach the outcome of many
widely used predictive models of invasion ecology. The complexity of natural systems
and interspecific relationships dilute such predictions with a substantial margin of error.
Prolonged field observations and rigorous data collection remains the most accurate
method for assessing the potential impact of invasive species on native ecosystems. In
fact, general scientific literature on yellow flag iris’ effect on Pacific Northwest ecology
remains scarce. Substantial knowledge gaps regarding the impacts by yellow flag iris
could be bridged by conducting further research with respect to Pacific Northwest
ecology.

4.3.3 Sediment Loads
Because yellow flag iris mostly inhabits low-lying marshlands rather than high
streambanks, the threat of erosion by this species is not a concern widely expressed in the
available literature. Though, the ability of this aggressive invader to trap sediment has
been the topic of much discussion in invasion ecology circles. Due to its tendency to form
dense rhizome mats, yellow flag iris can effectively collect suspended solids that flow
through a stream. This sediment retention can eventually lead to a narrowing of stream
channels and increase flow velocities, thereby increasing the sediment carrying capacity
of lotic water bodies (Spaak, 2016). There exists a potential for drastic hydrologic
obstruction if infestations of yellow flag iris are permitted to encroach into the central
region of a flow field. When this occurs, yellow flag iris can sprout new plants from

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rhizomes to form a figurative wall of tangled rhizomes, leaves, and stems that spans the
width of the stream (Figure 19).

4.3.4 Stream Chemistry
This aggressive invasive flowering plant possesses potent chemistry which may
adversely impact aquatic organisms, though most studies on this subject are inconclusive.
Yellow flag iris contains various compounds which are toxic to animals and humans. The
glycoside content in yellow flag iris has been attributed to its general unpalatability for
grazing animals and can cause harmful gastrointestinal effects when consumed (Jacobs et
al., 2010). Contact with its resin can cause skin irritations, and prolonged exposure can
even cause blistering (USFWS, 2019). It is difficult to discern the effects of chemical
inputs on aquatic organisms by yellow flag iris because of the complex nature and
abundance of the compounds it produces. Some of the chemicals contained in the tissues
of yellow flag iris have been extensively studied, while others have only recently been
verified to exist in this invasive plant.
A 2014 study analyzed eight different iris species to determine the presence or
absence of eleven chemical compounds (alkaloids [ALK], phenols [PHE], flavonoids
[FLA], quinones [QIN], proteins [PRO], saponins [SAP], cardiac glycosides [C. GLY],
glycosides [GLY], tannins [TAN], terpenoids [TER], and steroids [STE]) within their
tissues (Kaššák, 2014). The conclusion of this study indicated that, out of all eight iris
species assessed for presence of those eleven compounds, yellow flag iris had the
strongest results (Figure 20) (Kaššák, 2014).

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Figure 20: Chemical Compounds Within Tissues of Multiple Iris Sp.
Header Acronyms are the eleven chemicals listed as follows: alkaloids [ALK], phenols [PHE], flavonoids [FLA], quinones [QIN],
proteins [PRO], saponins [SAP], cardiac glycosides [C. GLY], glycosides [GLY], tannins [TAN], terpenoids [TER], and *steroids
[STE]. *STE is missing from this table; it may have been accidentally cut off from the original paper due to the large size of the table.
“Complete results from all the tests are in [this table]. Reactions were evaluated on a scale with six values. The best results, strongest
reaction, are marked with four plus marks (++++), samples without any reaction are marked with two minus marks (- -). Other
reactions are marked as follows: weak uncompleted reaction (-), weak reaction (+), strong reaction, but with some deficiencies in
coloration (++), strong reaction (+++). From the results we can see that the best result, the richest reactions were in the sample I.
pseudacorus ‘Roy Davidson’, rhizome from 2013[, while the] weakest reaction, the lowest content of researched chemicals has I.
pseudacorus, flower from 2013” (Kaššák, 2014, Table 1)

Since yellow flag iris contains high concentrations of reactive chemical
compounds and populations of this plant are most often found in or near aquatic
environments, its potential to chemically alter Pacific salmon habitat must be carefully
scrutinized. The effects that these compounds may have on salmon, as well as the
invertebrate prey species which they depend on for growth and development, is not yet
conclusive. Future research into the potential of this invasive wetland invader to

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contribute toxic chemicals to freshwater ecosystems in the Pacific Northwest must be
conducted in order to determine the full impact of yellow flag iris on salmon habitat.
Yellow flag iris has been effectively used as a phytoremediation method in
wetlands which receive high toxic inputs from sewage, urban runoff, and industrial
waste. A study conducted in Iran suggested that wetlands planted with yellow flag iris
could provide an effective secondary filtration for wastewater management and found
that it removed 51% to 74% of phosphorus, 48% organic nitrogen (TKN), and 67% to
75% of O-PO4 in constructed wetlands (Yousefi & Mohseni-Bandpei, 2010). Wang et al.
(2008), performed a previously similar experiment, which compared the contaminant
removal potential of yellow flag iris to those of common reed (Phragmites australis), and
broadleaf cattail (Typha latifolia). The scientists performing this study concluded that
yellow flag iris was inferior in its ability to remove total Kjeldahl nitrogen (TKN) and
statistically similar in removal of phosphorus when compared to Phragmites and Typha
species (Wang et al., 2008). Another project in 2012 tested the phytoremediation
potential of soft rush (Juncus effusus), reed canarygrass, yellow flag iris, and a mix of
grass seeds (25% tall fescue [Festuca arundinacea], 25% red fescue [Festuca rubra], and
50% perennial ryegrass [Lolium perenne]) in the removal of polycyclic aromatic
hydrocarbons (PAHs) (Leroy et al., 2015). This study concluded that yellow flag iris
provided high initial removal of PAHs, but in time this effect was damped, and the
contaminants began to concentrate in the lower substrate levels; all other plant species in
this study showed better long-term benefits of PAHs removal than yellow flag iris (Leroy
et al., 2015).

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Based on previous studies, yellow flag iris does appear to have some value in
removing and processing toxic compounds from contaminated sites, but when assessed in
the context of natural riparian ecosystems, the benefits of this invasive in providing high
quality water conditions remains questionable. The determination of how this plant
chemically impacts Pacific salmon habitat, comes down to a cost-benefit analysis; are the
capabilities of this plant to intercept and neutralize toxic compounds greater than its
negative chemical contributions to salmon habitat? Only further research will provide a
definitive answer to this question.

4.3.5 Water Flow Regimes
The ability of yellow flag iris to clog waterways has been widely accepted as a
common trait of the plant by many environmental restorationists and invasive ecologists.
The potential effects that this invasive plant may have on water flow, flooding, and
stream obstruction have been frequently observed in wetlands throughout the world, yet
definitive studies on this subject are rare. The obstructive capability of this aggressive
plant resides in the robust architecture of its extensive rhizome networks, which often
form in subsurface net-like structures.
Single clones from yellow flag iris rhizomes can commonly form masses up to
four feet in diameter (Simon, 2008). Tightly clustered mats of intertwined yellow flag iris
were observed growing in masses up to 20 meters (65.6 feet) across in Ireland
(Sutherland, 1990). Rhizome mats of yellow flag iris can be anchored to the substrate or
found in floating mats on the water’s surface (Jacobs et al., 2010), where they collect and
accrete drifting suspended matter and sediment. This depositional process can create
raised topography in areas of high yellow flag iris concentrations, and result in further
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increased sedimentation rates along the margins of a stream (Tu, 2003). In time, this can
lead to a narrowing of a stream channel, alterations to flood regimes, and negative
impacts to native species diversity.

4.3.6 Stream Temperatures
As previously discussed in Chapter 4.3.2, yellow flag iris has a strong tendency
to exclude other vegetative species in the areas which it dominates. By doing so this
invasive flower can limit the ecosystems services provided by many naturally occurring
riparian plants. In the Pacific Northwest, yellow flag iris commonly displaces many
native wetland tree species that provide shade to waterbodies by their large extensive
canopies. Like many of the previously discussed IVS that form monocultures in riparian
zones, yellow flag iris can drastically effect stream temperatures by increasing the
amount of solar radiation striking the water’s surface. Since this invasive plant neither
possesses a canopy to adequately shade streams nor permits the establishment and growth
of vegetative species that do, it must be viewed as an aggravating factor in rising water
temperatures that have become a major threat to salmon in Washington.

4.3.7 Shelter Abundance (Woody Debris)
Similar to many other invasive riparian plants which have the propensity to
produce monocultures in riparian areas, yellow flag iris greatly inhibits natural woody
debris recruitment into riverine environments. If left uncontrolled, this plant can form
dense colonies which severely diminish the abundance of large native trees which
normally provide stream shelter components to Pacific salmon in the form of DWD.
Since DWD plays such a significant role in the survival of juvenile salmon, any threat to

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that crucial aspect of salmon habitat must be considered a major hinderance to salmon
conservation efforts.

4.3.8 Migration Route Obstruction
The biological characteristics of this wetland perennial enable it to form massive
colonies of densely clustered material that can collect vast quantities of sediment in lotic
environments. This rate of sediment trapping is so extreme that it can raise the elevation
of local topography directly under yellow flag iris stands (Tu, 2003). Repeated deposition
in areas dominated by yellow flag iris often accumulate in layers that can be substantially
higher than the water level of the local environment. Sediments, which are released
during high flow periods, floods, or disturbance, can be efficiently intercepted by
substantial stands of yellow flag iris, thereby increasing the depth of sediment in low
velocity zones; in lotic systems, this typically occurs in the margins of the stream and
along the embankment (Gurnell et al., 2012). Yellow flag iris has been shown to narrow
stream channels and form raised vertical banks which are impenetrable by fish and large
aquatic organisms. In salmon bearing streams, yellow flag iris can substantially diminish
the area of available salmon habitat by limiting access to floodplains and lateral channels.

4.3.9 Predator Habitat
More work needs to address yellow flag iris’ ability to promote salmon predator
habitat. Future research to identify the potential connection of yellow flag iris to
predators, disease, pathogens, parasites, and parasitoids of Pacific salmon is strongly
recommended. It is possible that no connection exists, yet there should be research into
this subject to explain why such habitat does not exist.

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4.4 Brazilian elodea (Egeria densa)
Listed as a Class B noxious weed in Washington State in 1993, Brazilian elodea
(Egeria densa) has successfully established a substantial presence in most of the counties
west of the Cascade Range. Although this perennial submergent plant’s common name is
elodea, its taxonomic designation places it in the genus Egeria; it is not truly a species of
elodea. Native to South America, Brazilian elodea populations elsewhere in the world are
believed to have originated by escaped specimens from the aquarium trade (Darrin, 2009;
Drexler et al., 2021; Rimac et al., 2018; Tamayo & Olden 2014). Brazilian elodea has
spread to dozens of countries and has an established presence ranging from the southern
tip of South Africa to the Canadian Arctic circle (Matthews et al., 2014). This
submergent macrophyte thrives in lacustrine environments but has also become a
problem in several river basins in Washington. As of 2014, Brazilian elodea has been
reported in 27 separate water bodies in Western Washington (1WISC, 2016). Currently,
the observed population of Brazilian elodea in Washington consists of only male plants
which have become widely distributed strictly through vegetative reproduction
(KCNWCP, 2014). In the temperate Pacific Northwest climate, Brazilian elodea
experiences seasonal dieback in autumn and overwinters in a dormant state on the bottom
of the water body it inhabits (Matthews et al., 2014). In spring when water temperatures
reach approximately 10°C (50°F), resurgence of growth occurs (Thiébaut et al., 2016).
Brazilian elodea possesses long buoyant vertical stems with short internodes and
bright green leaves configured in whorls (Figures 21 - 24). Each whorl typically contains
four linear minutely serrated leaves (NWCB, 2014) that are one to three centimeters long
and around five millimeters (0.2 inches) wide (Walsh et al., 2013). Stems of Brazilian

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elodea are approximately one to three millimeters (0.4 - 1 inch) in diameter and can grow
to more than three meters long (Yarrow et al., 2009). Typically rooted one to two meters
(3 - 6.5 feet) below the water’s surface, this aquatic plant can also form floating mats or
exist as small fragments drifting in the water column (Yarrow et al., 2009). Fragments of
Brazilian elodea with as few as two nodes can sprout roots to form a new plant (Vincent
et al., 2016). This invasive macrophyte can negatively affect aquatic ecosystems by
displacing native plants and animals, altering water quality, increasing sedimentation
rates, and changing nutrient cycling regimes.
Brazilian elodea ranked the last out of the top four species from the survey results,
with 27% of respondents mentioning this invasive species as having a high impact on
freshwater ecosystems. When asked why this plant was specifically a priority,
respondents mentioned that Brazilian elodea:
1) easily clogs sloughs and small channels thereby blocking salmon migration
(75% of Brazilian elodea respondents),
2) is a widespread aggressive invader (50%),
3) is difficult to control and can have invasive management techniques
associated with the species (50%),
4) alters water chemistry, such as disrupting oxygen flow important to rearing
salmon, (50%),
5) considered costly to manage (25%),
6) can alter the predator/prey relationship (25%), and
7) overall, has impacts on freshwater (25%).

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According to field professionals, this invasive submergent macrophyte poses significant
harm to Pacific salmon habitat by clogging waterways, altering water chemistry and
dissolved oxygen concentrations, altering salmon-predator dynamics, and can be very
challenging to manage.

Figure 21: [photo] Egeria densa identification drawing
Drawing of Brazilian elodea by Christine Payne, from Sainty and Jacobs, 1988 (as cited in Bowmer et al., 1995).

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Figure 22: [photo] Comparison drawing of Hydrilla, Elodea, and Egeria
Drawing to identify Brazilian elodea “Egeria” to the far right (University of Florida Center for Aquatic and Invasive Plants, 1990).
(Cited with authors permission)

Figure 23: [photo] Brazilian elodea in flower
Photo of Egeria densa in flower taken by Hörður Kristinsson (Hörður K., 2010).

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Figure 24: [photo] Egeria densa proliferation
A combination of Egeria densa and Egeria najas; predominantly Egeria densa (William T. Haller, University of Florida,
Bugwood.org). This image was cited as specified by the author.

4.4.1 Dichotomy
The following dichotomy is taken directly from the second edition of the Flora of
the Pacific Northwest (2018), in which the genus Egeria begin on page 669 (Hitchcock &
Conquist, 2018).
Egeria (p. 669)
Plants staminate, pistillate; spathes axillary, sessile, 1-flowered; staminate flowers
with 9 stamens; pistillate flowers solitary, with pedicle-like hypanthium generally
elongating to bring rest of flower to the water surface, stigmas 3, generally 3-4
lobed, tending to float, the styles slender; fruits ovoid, smooth, irregular
dehiscent; seeds fusiform, mucilaginous; submersed, perennial herbs with rooting
stems and whorled, rarely opposite, sessile leaves.
E. densa Planch. Stems erect, 2-3 millimeters wide, rooting directly in substrate,
rhizomes lacking; main leaves 12-40 x 2-5 millimeters, mostly in whorls of 4(up
to 9), recurved, margins entire to finely serrate; staminate flowers 2-4(or 5) per
spathe, petals 8-10 millimeters; South American intro, commonly used in aquaria
and often planted or allowed to escape; in our area chiefly lowlands west
Cascades, south Vancouver Island to California, Blaine County, Idaho, and
central and eastern US

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4.4.2 Overall Biodiversity (Flora, Fauna, Invertebrates)
The competitive effects of Brazilian elodea on native Pacific Northwest
biodiversity have not been thoroughly studied, though there have been numerous claims
by ecologists and land managers of this invasive macrophyte rapidly displacing native
aquatic plant species in Western Washington (Darrin, 2009; Matthews et al., 2014; Rimac
et al., 2018; Yu et al., 2018). Quantitative data regarding Brazilian elodea’s effectiveness
to exclude native species remains uncommon in scientific literature. Based on the
scientific literature investigated during this project and the survey results, the following
section will attempt to relate the attributes of this aquatic invader to native biodiversity
reductions and the implications for salmon habitat.
Studies indicate that Brazilian elodea may not be a superior competitor when
compared to some other aquatic plant species. For example, Mony et al. (2007) provided
evidence that common hornwort (Hydrilla verticillata) may readily outcompete Brazilian
elodea in the presence of adequate nutrients, but the opposite is true in oligotrophic
conditions. Similarly, Pierini et al. (2004) conducted a study which indicates that
Brazilian elodea may be displaced by the closely related narrowleaf anacharis (E. najas)
when grown in water with low dissolved gas concentrations. Researchers performed
another experiment in Mongolia, China, examining the interspecific competition between
Brazilian elodea and the native submergent grass narrowleaf bur-reed (Sparganium
angustifolium) when grown in close proximity to each other (Yu et al., 2018). The
researchers planted the invasive Brazilian elodea in plastic pots with narrowleaf bur-reed
and also planted monoculture of each species as control samples. In this case,
Competition by narrowleaf bur-reed significantly reduced the growth of Brazilian elodea.

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By the end of the experiment, Brazilian elodea showed a decrease of 27.13% in ramet
abundance, 32. 76% in plant Height, 18.11% in root length, and total reduction in
biomass of 63.88% when compared to control samples (Yu et al., 2018).
Brazilian elodea does appear to have several physiological and biological
limitations which may indicate that it cannot survive for extended periods under extreme
circumstances. For example, this invasive plant experiences tissue damage at a
temperature below 3°C (37°F) or above 30°C (86°F) (Matthews et al., 2014). Brazilian
elodea is most often found in still or gently flowing waters and its stem tissues are easily
fragmented in higher water velocities (Coetzee et al., 2011). This plant is not tolerant of
water velocities over one meter (~ 3.3 feet) per second (Matthews et al., 2014).
Additionally, Brazilian elodea does not tolerate salinity concentrations greater than 0.5
parts per thousands (Poirrier et al., 2010). Considering that Pacific salmon contribute
seasonal salinity inputs to freshwater during post-spawning decay, further investigation
of Brazilian elodea’s compatibility in salmon habitat must be conducted. The sensitivity
of Brazilian elodea to these water quality parameters may indicate reasons why this IVS
was rated below knotweed, reed canarygrass, and yellow flag iris in the survey results.
Since Brazilian elodea has inherent susceptibility to the factors mentioned above, it may
not establish in areas where these conditions are present.
Despite these competitive shortcomings, Brazilian elodea has been shown to
aggressively outcompete many Pacific Northwest native aquatic plants and continues to
negatively impact ecosystems in the region. This aquatic invader may not be an apex
competitor in every environment, situation, or circumstance found in aquatic ecosystems;
yet, scientific research alludes to Brazilian elodea’s proficiency as an opportunistic

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dominator; an IVS which establishes substantial populations when and where
environmental conditions are optimal. By capitalizing on its inherent biological and
physiological strengths, Brazilian elodea has efficiently spread throughout the world from
its point of origin.
A New Zealand study by Wells and Clayton (1991) indicated that Brazilian
elodea may reproduce and spread at an alarming rate. At the initial introduction site in a
large lake, Brazilian elodea coverage increased from 10% to 100% in near shore areas
over the course of two years (Wells & Clayton, 2010). After five years, this invasive
macrophyte became the most abundant aquatic plant in the lake (Wells & Clayton, 2010).
Within six years the researchers showed that this prolific plant was able to establish in
96% of sampled sites (Wells & Clayton, 2010). The drastic displacement of native
vegetative species demonstrated in this study exemplifies the potential dangers of
Brazilian elodea on ecosystems which it dominates.
The biological characteristics and adaptive traits possessed by Brazilian elodea
may provide it with a competitive advantage over other native aquatic plants in the
Pacific Northwest. This aquatic invader has been documented to tolerate stressful
environmental conditions that many native species of Pacific Northwest plants may be
more sensitive to. For instance, Brazilian elodea demonstrates rapid growth in a high
temperature range between 16 to 28°C (61 - 82°F) but can also survive for extended
periods below ice (Matthews et al., 2014). Brazilian elodea has also shown a higher
competitive capacity in oligotrophic environments, where it allocates energy reserves into
tissue growth used for passive diffusion of soluble nutrients drifting within the water
column (Mony et al., 2007). Literature on photonic requirements of Brazilian elodea have

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conflicting perspectives. According to Barko and Smart (1981), this macrophyte is
intolerant of low light environments, where other researchers assert that it tends to
increase competitiveness in turbid dim waters (Yarrow et al., 2009; Rodrigues &
Thomaz, 2010).
In the San Joaquin River delta of California, Brazilian elodea has caused major
negative impacts to the local biodiversity and the economy since the 1980’s (Caudill et
al., 2019). A post restoration assessment of the region provides strong evidence for
resurgence of native species diversity and abundance following removal and control of
Brazilian elodea. During the invasive vegetation management project timeline, from 2006
to 2017, relative frequency of non-native plants significantly decreased while native plant
occurrence showed the opposite trend (Caudill et al., 2019). The successful control of
Brazilian elodea in the project area has translated to an overall prevalence of native
aquatic plant species in the San Joaquin River delta (Caudill et al., 2019). By 2017, native
plant frequency was observed at around 80% occurrence within the study area (Caudill et
al., 2019). These management efforts were predicted to improve native fish habitat, water
quality, and navigation within the waterway.
Brazilian elodea has been confirmed to alter the community composition of
certain species of invertebrates. A paper by Espinosa-Rodriguez et al. (2017) details the
allelopathic effects of Brazilian elodea on the abundance of three species of littoral
cladocerans (Diaphanosoma birgei, Macrothrix triserialis and Simocephalus mixtus), and
the pelagic cladoceran (Daphnia mendotae). This study established a strong correlation
between high abundance of cladocerans and the allelochemicals exuded by Brazilian
elodea (Espinosa-Rodriguez et al., 2017). Two of the cladoceran species showed an

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abundance increase three to four times higher than control studies with an absence of
allelochemicals (Espinosa-Rodriguez et al., 2017). This study provides one example of
how Brazilian elodea may alter the trophic structure in an ecosystem. If this manner of
change were to occur in Pacific salmon habitat, it could alter abundance of the
macroinvertebrate species which salmon depend on for growth and development.
Not all observable effects by Brazilian elodea on biodiversity are negative.
References within scientific literature cite the benefits to some cooccurring organisms.
Mazzeo et al. (2003) found that this macrophyte had a significant correlation to high
densities of certain species of zooplankton in an Uruguayan lake. The authors postulated
that these zooplankton were using Brazilian elodea for refuge from predators as well as a
feeding zone and the result may have been an increased rate of survival (Mazzeo et al.,
2003). Many bird species rely on Brazilian elodea for a substantial portion of their diet
during parts of the year. In its native range, this aquatic plant can constitute the majority
of the dietary consumption for the black-necked swan (Cygnus melancoryphus) (Corti &
Schlatter, 2002). Populations of several avifauna species in Florida have improved
hunting success and foraging opportunities while feeding in stands of Brazilian elodea
(Bartodziej & Weymouth, 1995). The benefits to Pacific Northwest wildlife due to
Brazilian elodea presence have yet to be documented.

4.4.3 Sediment Loads
Based on the literature reviewed for this project, it appears as though increases to
erosion rates do not occur as a direct cause of Brazilian elodea infestation. The survey
results confirm this account, as none of the respondents mentioned erosion or
sedimentation as a negative ecological impact caused by this IVS. Conversely, there
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exists evidence that Brazilian elodea may be effective at trapping and collecting
suspended sediments and organic materials. According to a study conducted on the San
Joaquin River delta California, Brazilian elodea accounted for 85% of the submergent
vegetation biomass in 2010 (Hestir et al., 2016). The researchers of this study asserted
that the proliferation of this invasive aquatic plant played a major role in the hydrological
sediment yield reductions experienced in the region since the mid-1900s, ranging from
-1.1% to -2.3% in turbidity per year (Hestir et al., 2016). In dense occurrences of this
invasive plant, yearly sedimentation rates in the San Joaquin delta were measured to
range from 1,103 to 5,989 grams per square meter (Drexler et al., 2021). Furthermore,
Brazilian elodea inhabits the littoral zone of waterbodies and does not impose influence
on riparian sediment inputs. Therefore, this invasive macrophyte does not contribute to
bank erosion as many other IVS discussed in this thesis do.

4.4.4 Stream Chemistry
Brazilian elodea can effectively alter the chemical composition of freshwater
ecosystems which it infests by altering nutrient cycling regimes, depleting DO, and
contributing organic materials during senescence. In regions with pronounced seasonal
variations, Brazilian elodea demonstrates clearly defined periods of growth and
senescence; although, in climates which do not feature significant temperature
amplitudes, this aquatic plant may persist as an evergreen perennial (NWCB, 2014).
When Brazilian elodea experiences senescence, it can cause various alterations to water
chemistry.
During autumn in temperate regions, this macrophyte typically loses the majority
of its biomass due to sloughing and decay of stems and foliage in response to shorter
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photoperiod and reduced temperatures (Matthews et al., 2014). Decomposition of organic
material consumes oxygen from the water column and releases nutrients which in turn are
consumed by various fungi, saprophages, and bacteria. This process of Brazilian elodea
decomposition and decay may have pronounced effects on the nutrient cycling regime,
potentially alters the trophic web, and reduces the aqueous oxygen supply in areas of
severe proliferation. In Pacific salmon habitat this could lead to a drastic change in
macroinvertebrate prey resource abundance and diversity as well as threaten the survival
of salmon. Careful study of such processes in the Pacific Northwest is required to
definitively quantify the impacts of Brazilian elodea on salmon habitat.
Confirmed observations of direct chemical contributions to freshwater
environments by Brazilian elodea have been documented. Through the exudation of
allelopathic compounds, this plant can significantly alter the chemical composition in
aquatic ecosystems which it dominates (Espinosa-Rodriguez et al., 2017; Fujii, 2009;
Wolters et al., 2019). Brazilian elodea is known to produce reactive chemical agents, but
the specific mechanisms involved have not been thoroughly investigated (Fujii, 2009).
Quantitative data regarding the number of compounds produced by Brazilian elodea and
the composition of allelochemicals was not discovered in the research while developing
this project. These allelochemicals appear to primarily suppress species of epiphytic algae
and cyanobacteria as a possible evolutionary competitive strategy (Wolters et al., 2019).
These chemicals also effect the abundance and diversity in some species of grazing
invertebrates that preferentially feed on the epiphytes (Espinosa-Rodriguez et al., 2017).
The full effect of allelochemical exudation by Brazilian elodea on Pacific salmon habitat
is poorly understood.

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The ability of Brazilian elodea to sequester nutrients directly from the water
column enables it to drastically transform the trophic dynamics of freshwater systems it
inhabits. Reddy et al. (1987) studied the effects of nutrient use by Brazilian elodea under
non-limiting nutrient conditions and found that the macrophyte preferentially assimilated
NH4 over NO3 when both ions were present (Reddy et al., 1987). The rate of nitrogen
removal increased significantly during summer months when compared to the winter
(Reddy et al., 1987). The researchers asserted that this was due to the alterations to water
chemistry by Brazilian elodea and an increase in NH3 volatilization during warmer
temperatures (Reddy et al., 1987).
Weragoda et al. (2009) published a paper in the Journal of Freshwater Ecology
discussing their experiment to study the nitrogen removal rate of Brazilian elodea. The
researchers determined that high densities of the aquatic plant, when grown in low
nutrient substrate, were able to remove 69% to 81% of soluble nitrogen, rendering the
system extremely oligotrophic (Weragoda et al., 2009). The scientists determined that the
mechanisms responsible for this efficient nitrogen removal by Brazilian elodea were NO3
assimilation as well as volatilization of NH4, into its gaseous form NH3 (Weragoda et al.,
2009). In fact, the results of this study indicated that upwards of 60% of nitrogen removal
occurred because of volatilization and emission into the atmosphere (Weragoda et al.,
2009).
Urrutia et al. (2000) provided one example of the severity and rapidity of nutrient
depletion by Brazilian elodea in a freshwater environment. By analyzing the sedimentary
layers in a Chilean lakebed, the researchers reconstructed the sedimentary history and
nutrient composition over the last 150 years (Urrutia et al 2000). Using core samples of

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the lakebed, and examining diatom community composition at each strata layer, the
scientists determined that the lake’s history was punctuated by three distinct periods of
trophic states (Urrutia et al., 2000). The first two periods, from 1883 to 1972, experienced
gradual shifts in species diversity and nutrient composition; the last period however,
featured an initial sharp increase in sedimentation and organic inputs (Urrutia et al.,
2000). The diatomic record indicated that around 1980, a drastic depletion of nutrients
occurred, which coincided with the first introduction of Brazilian elodea into the lake
(Urrutia et al., 2000). After careful analysis, the researchers asserted that the oligotrophic
conditions were caused directly by proliferation of Brazilian elodea.
The capability of Brazilian elodea as a potential phytoremediation species has
been reviewed by several scientific researchers (Abu Bakar et al., 2013; Harguinteguy et
al., 2015; Kobayashi et al., 2014; Mustafa & Hayder, 2021). Harguinteguy et al. (2015)
conducted a short duration seven-day study to compare the heavy metal removal ability
of parrotfeather (Myriophyllum aquaticum) and Brazilian elodea. This study indicated
that parrotfeather outperformed Brazilian elodea in almost every metric of the experiment
(Harguinteguy et al., 2015). The researchers noted that during Pb retention, Brazilian
elodea suffered photosynthetic dysfunction as a result of chlorophyl production inhibition
caused by Pb toxicity, whereas parrotfeather did not appear to be significantly affected
(Harguinteguy et al., 2015). In another study, Brazilian elodea was compared with
fanwort (Cabomba piauhyensis) and hydrilla (Hydrilla verticillata) in its ability to extract
As, Al, and Zn (Abu Bakar et al., 2013). The researchers determined that the Brazilian
elodea was highly efficient in removing As and Zn but was inferior to fanwort in its

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ability to remove Al (Abu Bakar et al., 2013). Like reed canarygrass, Brazilian elodea
may be effective for phytoremediation in some cases but not all.
The ultimate assessment of this IVS’ impact to stream chemistry in Pacific
salmon habitat may be determined only by carefully weighing the positive and negative
effects of its presence. Based on the literature reviewed for this thesis project, the
detrimental effects of this invasive macrophyte species appear to outweigh its benefits,
and thus, management of Brazilian elodea infestations in salmon habitat remains
warranted. This notorious global invader can reduce the concentrations of available
nutrients in the freshwater ecosystems it infests, especially during warmer seasons. It can
create low oxygen environments during seasonal senescence and decomposition of its
biomass. Yet, Brazilian elodea also has value as a phytoremediation species in some toxic
water conditions. More research into the ability of this aquatic plant to alter water
chemistry will only strengthen invasive species management and salmon conservation
efforts.

4.4.5 Water Flow Regimes
Defining characteristics of Brazilian elodea invasion include formation of massive
monotypic stands, sediment accumulation, and reductions to water flow. In fact, results
from the thesis survey indicated that this aspect of the invasive plant was the most
concerning for its proliferation in Western Washington. The literature reviewed
throughout this project confirmed the professional opinion that Brazilian elodea can
drastically reduce water flow and alter hydrologic function in freshwater environments
which it infests.

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The determining factors regarding any macrophyte’s ability to restrict water flow
include the physical structure of the plant and stand density (Wolters et al., 2019).
Brazilian elodea can clog waterways to the point at which adjacent land may be at risk of
flooding (Matthews et al., 2014). This aquatic plant is also capable of tremendous
primary production and forms dense standing biomass which can regularly reach
concentrations of 800 to 1,000 grams dry weight per square meter in optimal conditions
(Yarrow et al., 2009). Not only can the organic biomass of Brazilian elodea create flow
obstructions, but the high sedimentation rate of this macrophyte can also effectively raise
the elevation of the bottom surface of the water body it inhabits, thereby restricting water
flow further. An analysis of sedimentation in the San Joaquin River delta, California
determined that the rate of vertical sediment deposition caused by Brazilian elodea
ranged from 0.4 to 1.3 centimeters (0.2 - 0.5 inches) per year (Drexler et al., 2021).
Brazilian elodea has become a major problem in its native range, and each year
this macrophyte is directly responsible for substantial economic losses, due to its
tendency to impede water flow in municipal reservoirs and hydroelectric systems
(Barreto et al., 2000). This invasive aquatic plant poses a threat to the agricultural
industry by clogging irrigation channels and restricting water supply to crops (Matthews
et al., 2014). Considering these examples, the implications for adversely affecting Pacific
Salmon habitat must be taken seriously. Dams and culverts already impede salmon
passage; additional challenges on their way to and from spawning grounds decrease
survivability. The experts surveyed for this thesis expressed concern of this IVS’ ability
to impose negative impacts to water flow regimes in Western Washington, and the need
for including management of Brazilian elodea in salmon conservation strategies.

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4.4.6 Stream Temperatures
Although Brazilian elodea does not impact riparian vegetation and decrease
canopy cover the way that Knotweed, reed canarygrass, or yellow flag iris do, this IVS
can indirectly alter water temperatures in environments it infests. By reducing water flow,
this invasive macrophyte allows water to absorb solar radiation for a longer duration than
it would if it were flowing at higher velocities. This flow reduction can lead to thermally
stratified water bodies (Durand et al., 2016) and temperatures, which negatively impact
salmon survival. Additionally, floating mats of Brazilian elodea have a higher rate of
sunlight absorption than surface water does, due to their photosynthetic capabilities.
Santos et al (2009) provided evidence that the water temperature surrounding floating
canopies of Brazilian elodea can be 1 to 5°C (33 - 41°F) higher than in adjacent areas
without a presence of the invasive. This aquatic plant does not directly inhibit the
establishment of native riparian tree species that provide shade to streams; which could
explain why ‘increase to water temperature’ was not a priority factor expressed in the
survey results. Based on the literature reviewed for this thesis, Brazilian elodea’s effects
on stream temperatures does not appear to be of significant concern for salmon habitat.

4.4.7 Shelter Abundance (Woody Debris)
This criterion is not applicable to Brazilian elodea. Large wood recruitment into
salmon habitat is not affected by this invasive species.

4.4.8 Migration Route Obstruction
Since Brazilian elodea commonly grows in substantial stands of dense biomass, it
may effectively impede the navigation of large fish species (Darrin, 2009). In recent

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years, this aquatic IVS has become a major concern in many Western Washington salmon
migration routes, including the Chehalis River Basin, Columbia River Basin, Lake
Washington, Sammamish Lake, and throughout the Puget sound estuary (Morgan et al.,
2021). The responses from the survey indicated that water flow impediments and salmon
migration route obstruction are the highest priority concerns for this species.
The physical structure of this aquatic plant is such that it grows in densely packed
stands, dominating all available space. Brazilian elodea could potentially clog confined
areas of water flow and prevent salmon from advancing farther upstream during homing
migrations. Thus, while it can provide refuge for small fish and juvenile salmon, it may
obstruct migration of larger fish (Roberts et al., 1999).
Ecologists from the State of California Department of Boating and Waterways
(2006) conducted a field survey and recorded 14 separate species of fish commonly
observed within the stands of this Brazilian elodea. Although the San Joaquin Estuary
exists as a major Pacific salmon migration route, none of the fish species observed were
salmon (State of California Department of Boating and Waterways, 2006). In fact,
salmon migration route obstruction caused by this invasive plant was one of the points
explicitly outlined in the Brazilian elodea Control Program (State of California
Department of Boating and Waterways, 2006).
Brazilian elodea has the potential to drastically limit salmon access to available
habitat when left unmanaged. By dominating vast areas of littoral zones in lakes and slow
flowing waterbodies this invasive aquatic plant can limit passage opportunities for
populations of migrating salmon. For these reasons, Brazilian elodea must be considered
a substantial threat to Pacific salmon habitat.

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4.4.9 Predator Habitat
Many studies link the largemouth bass (Micropterus salmoides), a voracious
predator of salmon, and Brazilian elodea patches (Conrad et al., 2016; Ferrari et al., 2014;
Grossman et al., 2013). The largemouth bass is not native to Washington. Interestingly,
Ferrari et al. (2014) found that in locations of dense Brazilian elodea patches, adult largemouth bass tended to have a reduced foraging ability, while juvenile largemouth bass
utilized the elodea as habitat as well as protection from the adult bass, which may suggest
an advantage for juveniles who also feed on salmon.
Another predator of salmon is the northern pikeminnow (Ptychocheilus
oregonensis). This predatory fish species is native to Washington and has been shown to
hide in Brazilian elodea, effectively ambushing salmon as they swim above (Celedonia et
al., 2008). Brazilian elodea also provides cover allowing the northern pikeminnow to hide
from predatory birds (Celedonia et al., 2008). To help salmon populations, the Pacific
States Marine Fisheries Commission has offered monetary rewards for catching northern
pikeminnow (Pacific States Marine Fisheries Commission, 2021).

Chapter 5: Conclusion
The information contained within this work provides a wealth of knowledge from
the fields of invasive vegetation ecology and Pacific salmon conservation. This thesis
project answered the question: Which invasive vegetative species have the greatest
negative impact on Western Washington’s freshwater salmon habitat in 2021? To answer
this question, I explored the literature and surveyed professionals. The following
subsections detail a recap of the thesis information (Chapter 5.1), overarching

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management of IVS (Chapter 5.2), and the future direction for this ongoing project, such
as the ways in which this project can be best utilized in future salmon habitat
enhancement efforts (Chapter 5.3).

5.1 Thesis Recap
As a result of this research, I narrowed down a list of 52 potential Western
Washington invasive vegetative species to the four most impactful on Pacific salmon
habitat (Appendix B). Based on survey responses, these four species were ranked in the
following order based on the survey results: knotweed, reed canarygrass, yellow flag iris,
and Brazilian elodea.
Industry professionals, mentioned that knotweed was highly detrimental to
salmon habitat due to its prolific occurrence and severe ecological destruction. The
literature collected supported the results of the survey. Knotweed aggressively
outcompetes native vegetation, commonly forms monocultures, triggers erosion events,
can deplete ecosystems of nutrients, and reduces native biodiversity.
Reed canarygrass negatively impacts the quality of Pacific salmon habitat by
altering stream morphology, displacing native wetland species, and limits stream channel
accessibility to salmon. The literature coincided with these survey results as well as
brought forth additional information on this IVS’ influence on salmon habitat. For
instance, one author suggested that reed canarygrass has extremely high-water use
requirements, which can reduce local hydrologic resources in areas of infestation. Reed
canarygrass was shown to be a useful phytoremediation species for environmental heavy
metal extraction. The most notable traits possessed by this IVS were ability to trap
sediment in its root mats as well as to alter stream temperatures by impeding the flow of
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water. Some evidence suggested that reed canarygrass could provide suitable habitat for
the invasive northern pike, which preferentially preys upon salmon.
The majority of survey respondents cited aggressive proliferation as yellow flag
iris’ most notable negative trait, while the minority noted changes to hydrology. Cross
referencing the literature did not confirm the survey results; there was an abundance of
anecdotal accounts but a lack of quantifiable data. However, the literature reviewed did
provide additional information on reed canarygrass, such as the plant’s toxicity to both
humans and livestock, and its use in phytoremediation. Furthermore, this plant’s ability to
obstruct water flow and block salmon migration routes was underrepresented in the
survey results when compared to the available literature.
Quantifying the effects of Brazilian elodea on Pacific salmon habitat was
complicated, since it was the least represented species in the survey results and had
limited scientific literature associated with it. This IVS is an opportunistic competitor,
one which only thrives when conditions are optimal, and in the absence of extreme
adversity. Literature revealed that this invasive plant possessed intolerance to adverse
environmental conditions. Cascading effects have been associated with Brazilian elodea’s
seasonal growth cycles; first, altering stream chemistry during senescence, which can
alter macroinvertebrate abundance and diversity, and ultimately affecting the survival of
salmon. The literature suggested that this macrophyte can drastically alter nutrient
cycling regimes by directly absorbing nutrients from the water column. The research
referenced alluded to Brazilian elodea’s ability to increase water temperatures by slowing
water velocities and photosynthesizing at the water’s surface. Furthermore, this invasive
plant has been documented to provide habitat to salmon predators, such as the non-native

150

largemouth bass and the native northern pikeminnow. As a result of these impacts, this
IVS must be controlled when found near salmon migration routes, and it must not be
allowed to spread into waterbodies used by salmon at any life stage.

5.2 IVS Management
The goal of management for IVS relies on a series of steps determined by the
species’ current degree of proliferation in an area (Figure 25). As an invasive, or
undesirable plant species, becomes more established in an area, the management shifts
between prevention, eradication, containment, and asset-based protection (Victorian
Department of Primary Industries, 2010). Prevention typically occurs before any species
arrives and is the most cost-effective option (Figure 5). Prevention is also the most
difficult approach because it is not easy to predict when and where a plant will become
established. Class A noxious weeds fall into the eradication approach as they have
populations that are small and thus easiest to control. Eradication involves the removal of
all viable individuals in an ecosystem. Often this removal consists of either chemical,
mechanical, or cultural methods – or a combination thereof. Class B noxious weeds are
generally managed under the containment approach which still includes eradication of
smaller satellite populations, as well as preventing the spread of the current larger
populations. There are some cases in which Class C noxious weeds are also managed
with the containment approach, depending on location and abundance. The majority of
Class C noxious weeds are managed under the approach of asset-based protection. Assetbased protection consists of preventing further encroachment of the invasive into the
desired plant populations while simultaneously promoting the spread of those desirable
species, such as native plants, into the area currently inhabited by the invasive vegetation.

151

Figure 25: Stages of IVS management
These are the various management stages that occur as infestations increase. For instance, once prevention is no longer an option the
best management is for eradication, but as the species proliferation increases containment becomes the next viable option, and so on
(Victorian Department of Primary Industries, 2010).

5.3 Next Steps
Management of IVS yields the greatest benefit when all stakeholders work
together. I have prepared this thesis so that agencies, groups, organizations, and others
can easily access information and a multitude of scientific resources that could help direct
management decisions or funding. It is my hope that science researchers may choose to

152

pursue research to fill the knowledge gaps outlined within this body of work. For
instance,
•

What are the specific mechanisms that are at work which increase the rate of
erosion in knotweed infested areas?

•

How does prolonged occurrence of knotweed impact soil chemistry and nutrient
availability (i.e., nitrogen, phosphorous, carbon)? If soil nutrient depletion is
confirmed by knotweed presence, does that translate to a reduction in aqueous
nutrients derived from soil?

•

Is alteration to water quality parameters (such as pH and DO) a feature of
knotweed?

•

What are the exact processes involved with knotweeds widely understood ability
to alter water flow regimes, such as increased flood risk, water flow reduction,
and stream obstruction?

•

Are there salmon predators that use knotweed and/or yellow flag iris as available
habitat? If so, what predator species reside in knotweed or yellow flag iris?

•

Does reed canarygrass produce high enough concentrations of alkaloid
compounds, primarily Phenols, Indoles, and β-carbolines, to impact Pacific
salmon habitat?

•

Does yellow flag iris produce high enough concentrations of toxic compounds
(Chapter 4.3.4) to impact Pacific salmon habitat?

•

Is there a statistical correlation between water flow/flooding/stream obstruction
and yellow flag iris?

153

•

Does Brazilian elodea displace native vegetation to the degree that it could be
detrimental to Pacific salmon habitat?

While many of these questions have been answered anecdotally, scientific studies of
these questions will provide a more complete understanding of Pacific Northwest
invasion ecology. Furthermore, they will provide an opportunity for individuals who are
not working in this field to learn more about invasive species and why it is so important
to help manage them. I also recommend that landowners reach out to their county
Noxious Weed Control Board to learn more about what they can do on their own
property. Additionally, the public has the opportunity to be citizen scientists by
downloading the Washington Invasive Species reporting app (Figure 26). Observing
invasive species and reporting the findings helps with early detection and rapid response
(EDRR) and assists ecologists with knowing where to focus management efforts.

Figure 26: [photo] Invasive Species Application Reporting
Download the WA Invasive Species app and report your findings. This is one of the best ways the public can help in the war on
invasives. Image used with permission by Alexis Haifley, Education Specialist with the Invasive Species Council (Haifley, 2020).
Image cited with permission.

This thesis may be written, but the project is not over. I want to reach out to each
of the county Noxious Weed Control Boards to gather the data they have on the locations
of these four IVS. By gathering this data, many of the tables will need to be updated
periodically, which I plan to do as the information becomes available. These updates will
be published within the ArcGIS story map created for presenting this thesis and is shared
as a link in the Abstract. The information will continue to evolve, as well as become
154

more refined in scale. This data should be used by everyone, from the environmental
enthusiast to the consummate professional.

155

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effects of climate change on Pacific salmon. Ecological Modelling, 397, 95-106. Doi:
https://doi.org/10.1016/j.ecolmodel.2019.02.002

188

Appendices
Appendix A: Survey Part I
2021 Survey of Freshwater Priority Noxious Weeds Impacting Salmon Habitat in
Western Washington
Survey Introduction
This survey has been created by a current Master of Environmental Studies student at
Evergreen State College working on a thesis project in collaboration with a team of
professionals specializing in related fields; including the WA Invasive Species Council,
the WA State Noxious Weed Control Board, WA State Department of Ecology, WA
State Department of Agriculture: Pest Program, and the Salmon Section of the Recreation
and Conservation Office. This survey is designed to seek additional expert knowledge to
identify high priority riparian and estuarine noxious weeds within western Washington
that affect ecosystem services as well as salmon bearing streams and salmon habitat.
Additionally, this survey is designed to compile pre-existing peer reviewed research and
documented information that may be already associated with the invasive vegetative
species inquired herein. We greatly appreciate your input and look forward to reading and
analyzing your responses. The answers provided from this survey will go far to help with
invasive vegetation management, as well as addressing funding gaps and possible future
funding opportunities. If you have been given this survey, it is because you have been
chosen as somebody who is valuable to this survey and your responses will be
greatly appreciated. Please read the letter of consent and confidentiality agreement so
that you know how your information will be used and how your privacy will be
protected. If possible, please have this survey filled out and submitted by February 1st
at the latest.
Once the survey has been started, you may not be able to come back to it or start a new
survey... please allow for a minimum of 15 minutes to complete this survey (more time
may be needed if answering information about multiple species or if the information is
not readily available).
1. Dear [Participant]:
I am a student at The Evergreen State College (ESC). As part of my thesis work in the
program, Master of Environmental Studies (MES), I will be conducting a research project
titled “Determining the top five most impactful noxious weeds affect freshwater
salmon habitat in western WA in 2020: A literature review and surveying
professionals”. The purpose of my project is to provide a bridge between various
stakeholders to maximize efforts/strategies/funding in the eradication/management of the
most impactful noxious weeds to ecosystem services within salmon habitats. I will be
conducting an online survey over the next couple months.
Any risks to you are minimal. I plan to minimize the risks/discomforts by 1) providing
189

complete information about the study, 2) coordinating with team of related
professionals about this study, and 3) removing individual names from the final
report. There will be no compensation of any kind available for your participation,
which is completely voluntary. You may withdraw your participation at any point or skip
any question you do not wish to answer without penalty. You may not directly benefit
from this research; however, we hope that your participation in the study may better
allow for a healthier environment and for species like the salmon species and
resident orca whales to be around for future generations.
Your answers will not be linked with your name. However, I may share your answers
with Shawn Hazboun, PhD (MES professor at ESC); John Withey, PhD (MES professor
at ESC); Kevin Francis, PhD (MES director at ESC); Mary Fee (Washington State
Noxious Weed Control Board); Justin Bush (Washington Invasive Species Council);
Chad Phillips (Washington State Department of Agriculture Pest Program); Alice Rubin
(Recreation and Conservation Office Salmon Section); Lizbeth Seebacher (Washington
State Department of Ecology); and Jennifer Parsons (Washington State Department of
Ecology).
As mentioned above, I will use your responses as resource material for my research
project on determining the top five most impactful noxious weeds affect freshwater
salmon habitat in western WA in 2020. At your request, I will provide you with a copy
of the thesis paper as well as any supporting aides, such as documentation or story-maps,
as well as an invitation to the thesis presentation delivered to the ESC and any other
presentation venue that occurs within the first year of finishing the thesis.
Your survey answers, collected as part of the research, could be used for future research
studies or distributed to another investigator for future research studies, with all
identifiable information removed, without additional informed consent from the subject
or the legally authorized representative.
If you have any questions about this project or your participation in it, you can call me at
253.XXX.XXXX (cell). My email address is keepingusgreen@yahoo.com. If you have
questions concerning your rights as a research subject or experience problems as a result
of your participation in this project, contact Karen Gaul, IRB administrator at The
Evergreen State College, Library 2008, Olympia, WA 98505; Phone 360.867.6009.
Thank you for your participation and assistance!
Sincerely,
Danielle Kies

190

-----Letter of Consent----I, ____, hereby agree to serve as a subject in the research project titled “Determining the
top five noxious weeds that affect freshwater salmon habitat in western WA”. It has been
explained to me that its purpose is to generate a list of the most impactful invasive
vegetative species to ecosystem services within salmon habitats.
□ Agree
□ Disagree

2. ------Confidentiality Form-----You are being invited to participate in a research study titled “Determining the Top Five
Invasive Vegetation Affecting Freshwater Salmon Habitat in Western WA”. This
study is being done by Danielle Kies from The Evergreen State College.
The purpose of this research study is to generate a list of priority species for
interagency collaboration in riparian management efforts across Western WA. If
you agree to take part in this study, you will be asked to complete an online
survey/questionnaire. This survey/questionnaire will ask about noxious weeds that you
are familiar with and it will take you approximately 5-20 minutes to complete, depending
on how much information you are willing to incorporate into your answers.
You may not directly benefit from this research; however, we hope that your participation
in the study help to promote a healthier environment for species like salmon and the
resident orca whales to have an increased chance to be around for future
generations.
Risks to you are minimal and are likely to be no more than mild discomfort with sharing
your opinion. To the best of our ability your answers in this study will remain
confidential. With any online related activity, however, the risk of a breach of
confidentiality is always possible. We will minimize any risks by 1) providing complete
information in the protocol regarding the experimental design and the scientific
rationale underlying the proposed research, 2) participating in regular meetings
with a team of related professionals about this study, 3) ensuring that the projected
sample size is sufficient to yield useful results, and 4) removing any grouping final
results so that no individual names are known in the final product. Your participation
in this study is completely voluntary and you can withdraw at any time. You are free
to skip any question that you choose.
Your survey responses, collected as part of the research, could be used for future research
studies or distributed to another investigator for future research studies, with all

191

identifiable information removed, without additional informed consent from the subject
or the legally authorized representative.
If you have questions about this project or if you have a research-related problem, you
may contact the researcher(s), Ms. Danielle Kies, 253.XXX.XXXX (cell),
KeepingUsGreen@Yahoo.com. If you have any questions concerning your rights as a
research subject, or you experience problems as a result of participating in this research
project, you may contact Karen Gaul, IRB Administrator at The Evergreen State College
at 360.867.6009 or irb@evergreen.edu.
By clicking “I agree” below you are indicating that you are at least 18 years old, have
read and understood this consent form and agree to participate in this research study.
Please print a copy of this page for your records.

□ I agree

□ I do not agree

3. Please provide your contact information:
Name (optional) (open text box)
Organization or Agency Represented (recommended) (open text box)
Area of Work: i.e. County, WRIA, Region (recommended) (open text box)
Email Address (optional) (open text box)
Phone Number (optional) (open text box)

4. What type of organization are you associated with? (drop down list of the following
options: County Conservation District, County Noxious Weed Control Board,
Educational Institution, Federal Agency, Non-Profit, Salmon Recovery Funding Board,
State Agency, Tribal, Other- please specify)
*If you choose other, there will be a textbox to write in your answer.

5. Would you like to participate and/or be included in further discussions about this
project?
*Some form of contact information (i.e., name & email address from Question 3) will be
required for inclusion in future activities/information.

□ Yes
192

□ No

6a. In your opinion, what are the priority noxious weed species and why. Please
ONLY select species that are within Washington State AND can be found in the
freshwater ecosystems. Select one species at a time.
*After submitting responses for the first species you picked, there will be a page
prompting you to continue with another species or finish the survey.
**Please only add up to ten different species total.
***Information about Washington State noxious weeds can be found at:
https://www.nwcb.wa.gov/classes-of-noxious-weeds.

193

Appendix B: Species List
List of species included in survey; *Top 4; **Top 11
Organized by: Class; Number of surveys mentioned; common (scientific names)
[Between class and name is number of survey responses]
A

0

A

1

A

0

A

3

A

0

B

4

B

2

B

2

B

3

B

0

B

0

B

0

B

10

B

3

B

0

B

1

B

2

B

0

B

1

B

0

B

0

B

1

B

1

B

1

B

0

194

common crupina
(Crupina vulgaris)
cordgrass (4 species – all class A)
(Spartina spp.)
floating primrose
(Ludwigia peploides)
**flowering rush
(Butomus umbellatus)
garlic mustard
(Alliaria petiolata)
*Brazilian elodea
(Egeria densa)
**butterfly bush
(Buddleja davidii)
**common reed
(Phragmites australis)
**Eurasian watermilfoil
(Myriophyllum spicatum)
European coltsfoot
(Tussilago farfara)
fanwort
(Cabomba caroliniana)
garden loosestrife
(Lysimachia vulgaris)
*Knotweed (4 species- all class B)
(Polygonum spp.)
**parrotfeather
(Myriophyllum aquaticum)
poison hemlock
(Conium maculatum)
policeman’s helmet
(Impatiens glandulifera)
**purple loosestrife
(Lythrum salicaria)
saltcedar
(Tamarix ramosissima)
Scotch broom
(Cytisus scoparius)
shiny geranium
(Geranium lucidum)
spurge laurel
(Daphne laureola)
tansy ragwort
(Jacobaea vulgaris)
water primrose
(Ludwigia hexapetala)
yellow archangel
(Lamiastrum galeobdolon)
yellow floatingheart
(Nymphoides peltata)

A, B

0

A

0

A

1

A

0

A

0

A

0

C

0

C

0

C

0

C

0

C

0

C

1

C

1

C

1

C

0

C

0

C

3

C

0

C

1

C

0

C

0

C

7

C

1

C

0

C

0

C

5

Knapweed (2 = class A; 6 = class B)
Centaurea spp. & Rhaponticum repens (B)
giant hogweed
(Heracleum mantegazzianum)
hydrilla
(Hydrilla verticillata)
ricefield bulrush
(Schoenoplectus mucronatus)
small-flowered jewelweed
(Impatiens parviflora)
variable leaf milfoil
(Myriophyllum heterophyllum)
Canada thistle
(Cirsium arvense)
common St. John’s wort
(Hypericum perforatum)
common tansy
(Tanacetum vulgare)
common teasel
(Dipsacus fullonum)
curlyleaf pondweed
(Potamogeton crispus)
English ivy
(Hedera sp.)
Eurasian watermilfoil (hybrid)
(Myriophyllum spicatum x M. spicatum)
evergreen blackberry
(Rubus laciniatus)
field bindweed
(Convolvulus arvensis)
fragrant waterlily
(Nymphaea odorata)
**Himalayan blackberry
(Rubus bifrons)
Japanese eelgrass
(Nanozostera japonica)
non-native cattail
(Typha sp.)
old man’s beard
(Clematis vitalba)
pampas grass
(Coraderia selloana)
*reed canarygrass
(Phalaris arundinacea)
Russian olive
(Elaeagnus angustifolia)
spotted jewelweed
(Impatiens capensis)
tree-of-heaven
(Ailanthus altissima)
*yellow flag iris
(Iris pseudacorus)

Appendix C: Survey Part II
*Question numbers may be different depending on which species was chosen to report
on, as each species has its own version of the following questions.
7. In your opinion, why is this species a high priority for freshwater management?
(open text box)
8. Date noxious weed was first discovered. Skip or select clear if unknown.
(date box with calendar attachment)
9. Which county is the invasive species located in?
(drop down box of Washington State counties)
10. To the best of your knowledge, approximately how many acres are currently
known to be infested within your watershed? *amount based on plant density rather
than total land coverage.
(multiple choice of ranges from: 0-5 acres; 5-10 acres; 10-25 acres; 25-50 acres;
50-100 acres; 100-200 acres; over 200 acres; unknown; other (please specify))
11. To the best of your knowledge, approximately how many total acres within the
watershed are known to be impacted (for example, additional acreage that could
potentially be infested or close to a vector of spread)?
(see same option choices as Q10)
12. To the best of your knowledge, approximately how many acres (of those infested)
are currently known to be actively managed/controlled?
(see same option choices as Q10, with an additional ‘does not apply’ option)
13. In your opinion, does the amount of current research available adequately meet
your agency’s needs (i.e., peer reviewed papers, documented research, etc.)?
(slider bar from 0 – 100; where 0 is “No research available”, around the middle is
“some research, but more needed”, and 100 is “More than enough research
available”)
14. Please include any available resources, such as a research project or peer
reviewed article, that can attest to the impacts of any of the before mentioned
species.
(open text box)
15. If you have any additional information regarding this species, please state it here
(for example, multiple counties or WRIA information).
(open text box)

195

Appendix D: Survey Part III
17. Out of all the species you have reported in this survey, please list them in order
of importance, with the first species listed as the one you feel is most important to
focus on.
(open text box)
18. Do you have any additional questions, comments, or concerns?
(open text box)
19. How easy or difficult was this survey to navigate?
(5-point Likert scale ranging from very easy to very difficult)
20. Comments
(open text box)
Thank you very much for your time and important information! Your contributions
are greatly appreciated.

196

Appendix E: Study Maps
Appendix E1: Study Area of Western WA Counties
Study area map of the nineteen Western Washington counties and their corresponding
acreage rounded to the nearest thousand acres.

197

Appendix E2: Western WA Chinook Streams
Chinook salmon (Oncorhynchus tshawytscha) streams classified by salmon stages. There
are just over 16,500 miles of streams for Chinook in Western WA.

198

Appendix E3: Western WA Chum Streams
Chum salmon (Oncorhynchus keta) streams classified by salmon stages. There are just
over 11,300 miles of streams for Chum in Western WA.

199

Appendix E4: Western WA Coho Streams
Coho salmon (Oncorhynchus kisutch) streams classified by salmon stages. There are just
over 22,000 miles of streams for Coho in Western WA.

200

Appendix E5: Western WA Pink Streams
Pink salmon (Oncorhynchus gorbuscha) streams classified by salmon stages. There are
almost 7,600 miles of streams for Pink in Western WA.

201

Appendix E6: Western WA Sockeye Streams
Sockeye salmon (Oncorhynchus nerka) streams classified by salmon stages. There are
almost 3,400 miles of streams for Sockeye in Western WA.

202

Appendix E7: Western WA Steelhead Streams
Steelhead salmon (Oncorhynchus mykiss) streams classified by salmon stages. There are
just over 24,500 miles of streams for Steelhead in Western WA.

203

Appendix E8: Top Four IVS Locations
Map of four noxious weed locations in Western WA. These noxious weeds include
Brazilian elodea (Egeria densa), yellow flag iris (Iris pseudacorus), reed canarygrass
(Phalaris arundinacea), and Japanese knotweed (Reynoutria japonica). To see these
various IVS counts by county, please refer to Table 4.

204

Appendix E9: IVS Presence on Chinook Streams
The locations where the top invasive vegetative species are within 200 feet of chinook
streams.

205

Appendix E10: IVS Presence on Chum Streams
The locations where the top invasive vegetative species are within 200 feet of chinook streams.

206

207

Appendix E11: IVS Presence on Coho Streams
The locations where the top invasive vegetative species are within 200 feet of coho streams.

208

Appendix E12: IVS Presence on Pink Streams
The locations where the top invasive vegetative species are within 200 feet of pink streams.

209

Appendix E13: IVS Presence on Sockeye Streams
The locations where the top invasive vegetative species are within 200 feet of sockeye streams.

210

Appendix E14: IVS Presence on Steelhead Streams
The locations where the top invasive vegetative species are within 200 feet of steelhead streams.

211

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Thesis_MES_2021_Kies.pdf