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AN ANTHROPOCENE ISLAND FLORA: THE FATE OF NATIVE AND ALIEN
PLANTS IN THE SAN JUAN ISLAND ARCHIPELAGO

by
R. Adam Martin

A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
June 2022

© 2022 by R. Adam Martin. All rights reserved.

This Thesis for the Master of Environmental Studies Degree
by
R. Adam Martin

has been approved for
The Evergreen State College
by

________________________
John Withey, Ph. D.
Member of the Faculty

________________________
Date

ABSTRACT
The core premise of the Anthropocene is that we have unintentionally altered the
earth so much that we have entered a new geological period. One of the most concerning
of these unintentional consequences is the widespread movement of species across
continents. This movement is causing natural communities to become simpler and more
self-similar, a process called biotic homogenization. This thesis explores how much
biotic homogenization is occurring and could occur in the future within the flora of the
San Juan Island archipelago of Washington State, which is a hotspot of floristic diversity.
This thesis addresses five main questions 1) what proportion of the flora are alien species,
2) are rare species disproportionately impacted by alien species, 3) what factors influence
the number and distribution of alien species, 4) how much biotic homogenization could
occur in the future, and 5) is biotic homogenization occurring now?
Currently, alien species comprise between 38 and 47% of the San Juan Island flora, and
most alien species present are invasive in other parts of the United States. Invasive
species are most common in meadow habitats which also have the greatest number of
rare and imperiled species. The most important factors determining the frequency of alien
species are residence time, invasiveness, island size, and how impacted the island is by
human development. In addition, because most of the alien flora has recently arrived, the
future flora could become up to 20% more similar by 2079. Finally, current evidence
suggests the most diverse small meadow islands are rapidly losing native species and
being mostly colonized by alien species. The synergistic impacts of invasive annual
grass, introduced Canada geese, and over-abundant black-tailed deer are hastening this

change. However, each island is changing uniquely, currently causing no directional
change towards homogenization or differentiation.

TABLE OF CONTENTS

Introduction ....................................................................................................................... 1
The Importance of Biotic Homogenization ................................................................ 6
Addressing the Darwinian and Wallacean Shortfalls ................................................. 7
What drives the colonization of alien species? ......................................................... 10
Positionality on alien species and conservation ........................................................ 11
Analytical framework ............................................................................................... 15
Chapter summaries.................................................................................................... 16
Chapter 1 – Invasion Debt and extinction Risk of vascular plants in the san juan
archipelago....................................................................................................................... 18
Introduction................................................................................................................... 18
Methods ......................................................................................................................... 22
Study Area ................................................................................................................ 22
Compiling the regional flora ..................................................................................... 25
Estimating total species richness .............................................................................. 26
Question 1: Are the differences in species-area curves between Alien and native
taxa? .......................................................................................................................... 27
Question 2: How at risk are imperiled species by invasive species .......................... 30
Question 3: Which alien plants have the greatest establishment debt? .................... 30

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Question 4: Homogenization Debt? .......................................................................... 38
Results ........................................................................................................................... 39
Describing the regional flora .................................................................................... 39
Current risks .............................................................................................................. 42
Biogeographic barriers .............................................................................................. 42
Factors influencing Alien Plant Species Frequency ................................................. 46
Future Homogenization ............................................................................................ 48
Discussion ..................................................................................................................... 50
Overall patterns within the flora ............................................................................... 50
Chapter 2 – Assessing Floristic change on small islands in the Southern San Juan
Archipelago ...................................................................................................................... 62
Introduction................................................................................................................... 62
The homogecene? ..................................................................................................... 62
Islands at risk ............................................................................................................ 63
Abiotic stressors ........................................................................................................ 66
Invasive species stressors .......................................................................................... 67
Methods ......................................................................................................................... 70
Location .................................................................................................................... 70
Field sampling ........................................................................................................... 71
Analysis ......................................................................................................................... 72
Results ........................................................................................................................... 77

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Question one: Do four components of plant community diversity within and across
the sampled islands change between the initial surveys and 2021?.......................... 78
Question Two: Do more native species become extirpated from islands rate than
alien species, and are they balanced by colonization? .............................................. 80
How do area, Canada geese, deer herbivory, and invasive annual grass influence
rates of community change? ..................................................................................... 83
Do the changes in species composition lead to biotic homogenization across the
sample islands? ......................................................................................................... 85
How does island area, the impact of invasive species, plant traits, plant nativity, and
phylogenetic relatedness influence the probability that a species will go extinct from
an island? .................................................................................................................. 86
Discussion ..................................................................................................................... 88
The Challenge of Scale ............................................................................................. 90
The Parable of Goose Island ..................................................................................... 93
Conclusion ................................................................................................................ 95
References ........................................................................................................................ 98

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List of Figures
Figure 1. Precipitation map of the Salish Sea.. .................................................................. 4
Figure 2. The number of herbarium collections of native and alien vascular plants within
the San Juan Island archipelago by decade. ........................................................................ 8
Figure 3. The proportion of herbarium collections within the San Juan Island archipelago
comprised of alien taxa by decade. ..................................................................................... 9
Figure 1-1. The study area. ............................................................................................... 24
Figure 1-2. Delineation of the search query of the Consortium of Pacific Northwest
Herbaria based on a polygon of the study area. ................................................................ 25
Figure 1-3. The number of observed and estimated species across four habitat species
pools in the San Juan archipelago. .................................................................................... 40
Figure 1-4. The status of 385 alien plant taxa documented within four habitat types found
in the San Juan Island archipelago, Washington State, USA.. ......................................... 41
Figure 1-5. Island size and richness relationship between native and alien species. ........ 44
Figure 1-6. Relationship of island size and richness between native and alien species
among four species pools; shoreline species, open (meadows and developed land),
forests, and wetlands.. ....................................................................................................... 45
Figure 1-7. Six predictors of island-specific alien species occurrence (probability of
occurrence).. ...................................................................................................................... 48
Figure 1-8. Increases in future alien species richness between 2022 and worst-case
projection for 2079. ........................................................................................................... 49

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Figure 1-9. Projected changes in the pairwise nestedness component of phylogenetic
beta-diversity for alien and native species between 2021 and 2179 (two human
generations). ...................................................................................................................... 50
Figure 1-10. Brodiaea rosea (Indian Valley Brodiaea), a Lazarus taxon not seen since
1908 and thought to be extirpated in Washington State, rediscovered in 2021................ 52
Figure 2-1. The dry southern face of Boulder Island in early June. ................................. 66
Figure 2-2. Left Panel: a rocky outcrop heavily impacted by Canada geese (Branta
canadensis) loafing, Male geese stand on prominent locations while guarding nest sites.
These sites largely devoid of plant life except invasive annual grass, weedy annual forbs
and dominated by geese feces. Right Panel: A typical disturbance around a goose nest.
Note the sparse vegetation, upturned soil and abundant feces.......................................... 69
Figure 2-3. Map of surveyed Islands along the southern shores of Lopez Island,
Washington USA. ............................................................................................................. 71
Figure 2-4. NMDS ordination displaying change in plant communities based on species
presences and absences and species cover for thirteen islands in the southern San Juan
archipelago.. ...................................................................................................................... 78
Figure 2-5. Overall change in four components of community composition across 13
islands in the southern San Juan archipelago. ................................................................... 80
Figure 2-6. Change in five components of community structure within 13 islands in the
southern San Juan archipelago.. ........................................................................................ 84
Figure 2-7. The change in plant community nestedness between island pairs (points)
among 13 islands between initial surveys in 2005-2009 and 2021. ................................. 85

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Figure 2-8. Two examples of difficult to capture impacts of deer and geese. In the left
image, vegetation has been extensively clipped, and flowers are short-stemmed from
extensive deer browse. ...................................................................................................... 91
Figure 2-9. Left image: an example of a ‘rock garden’ within a maritime meadow not yet
impacted by geese. Right image: a rock garden impacted by geese.. ............................... 92
Figure 2-10. Goose Island six years after a wildfire burned the entire island.. ................ 94
Figure 2-11. The view from the top of Swirl Rock in 2021, the site of where a small patch
of maritime meadow once persisted, home to one of the three populations of the rare
disjunct Oxytropis campestris var. spicata. ...................................................................... 95

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List of Tables
Table 1-1. The six models used to assess the relationship between island size and species
richness for native and alien species in shoreline, open, forested, and wetland habitats.. 28
Table 1-2. Candidate predictors of alien plant species frequency in the San Juan Island
archipelago. ....................................................................................................................... 33
Table 1-3. Ordinal scale of human impact on islands in the San Juan archipelago .......... 36
Table 1-4. Distribution of rare species across four habitat types found in the San Juan
Archipelago ....................................................................................................................... 40
Table 1-5. Kendall rank correlation coefficients for the relationship between rare native
species and invasive alien species across all island habitats (All) and among four habitat
types.. ................................................................................................................................ 42
Table 1-6. The top threshold model results for native and alien species across four
habitats.. ............................................................................................................................ 43
Table 1-7. Importance of nine variables in models predicting the number of islands an
alien species is present.. .................................................................................................... 46
Table 1-8. Bayes Factor t-test summary table. ................................................................. 49
Table 2-1. Summary of Overall demographic and ecological risk of the eight islands in
the study.. .......................................................................................................................... 65
Table 2-2. Results of t-tests comparing four community change components between two
time periods fit with Bayesian inference. ......................................................................... 79
Table 2-3. The change in plant richness and the number of colonizations and extirpations
for alien and native plants across 14 islands in the southern San Juan Island archipelago..
........................................................................................................................................... 81

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Table 2-4. The change in the incidence of rare species across 14 islands along Southern
Lopez Island between two survey periods. ....................................................................... 82
Table 2-5 Model importance values for four model parameters explaining five
community change components.. ...................................................................................... 83
Table 2-6. Importance of five model parameters predicting species extirpation. ............. 86

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Acknowledgements
Any large writing project is a community endeavor, especially during what
became a devastating three-year global pandemic, one that almost perfectly coincided
with my entire graduate experience. I often thought of what C.S. Lewis said in “Learning
in Wartime” (1939):
“If men had postponed the search for knowledge and beauty until they
were secure the search would never have begun. Plausible reasons have
never been lacking for putting off all merely cultural activities until
some imminent danger has been averted or some crying injustice put
right. But humanity long ago chose to neglect those plausible reasons.
They wanted knowledge and beauty now, and would not wait for the
suitable moment that never come. This is not panache; it is our nature.”
Thankfully, during this time of imminent catastrophe, I was and continue to be
blessed with several supportive and encouraging people who shepherded and mentored
me through both graduate school and writing this thesis.
First, I would like to thank Peter Dunwiddie for more than a decade of
mentorship, friendship, encouragement, and support. He first introduced me to island life
in the San Juans more than a decade ago when we rowed a boat out to a tiny island off
Lopez to plant golden paintbrush. This thesis would not have occurred had I not been on
that trip and taken by the beauty and oddities of those tiny rocks in the sea. One of the
great gifts of life is finding, apprenticing to, and having a mentor who helps bring out our
curiosity and passion – may I always be the kind of scientist, mentor, and person Peter
has been for me. Our adventures collecting plants in little-known or visited places in the
islands will be with me for my life.
Second, I would like to thank Katy Beck, Steve Ulvi, Peter Zika, and the
numerous folks who have for helping look for and document plants on many of the

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islands. Katy helped resurvey many islands in 2021. Steve was our intrepid and skilled
mariner. Peter Zika was a constant companion and mentor in the field and was vital to
understanding the sedge and other obscure plant taxa in the field and herbarium – to be so
lucky as to have a real-life plant taxonomist with you in the field. I am deeply grateful for
him and all the time he has spent on the islands looking for plants. His dog-eared and
deeply annotated copy of Atkinson and Sharpe’s flora was a treasure trove of
information. Finally, this thesis work rests on the shoulders of the many botanists and
curious naturalists that came before. In particular, the many folks part of the first
botanical inventories of the islands in the early 2000s – including David Giblin, Phil
Green, Eliza Habegger, and others. I also thank John Withey for so much positive
encouragement and helpful feedback and for taking the time to read through and help
craft this document. I also want to thank the Washington Native Plant Society for
financial assistance for field work; their contribution helped pay for boat time, making
fieldwork easier and possible. My work colleagues have also been a wonderful support,
encouraging me and letting me take the time needed to complete such a big project.
Lastly, I’d like to thank my partner Rebecca, who has been steadfast support, and
I surely could not have completed this without her. She forgave the many long days and
nights of me cloistered at the writing desk and weeks away doing fieldwork. She always
assured me and helped me remember the joy at the heart of learning through my many
periods of graduate school-induced stress and anxiety.

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DEDICATION
I dedicate this work to my grandparents, Ralph and Guida Martin, who passed on
many years ago but are always close to my heart. They were with me on all my island
adventures. My love of natural history stems from my Grandfather’s patience in
following a young boy among the cobble beaches of Maine, picking up hermit crabs and
periwinkles, scrambling among the hills and rocks of Acadia National Park, and catching
fire-flies in the backyard. My love for words, writing, and plants came from my
grandmother, an English teacher, who spent many mornings patiently working with me
through the newspaper word puzzles. She sent me on many missions out the door to pick
blueberries for muffins. The time eating berries among the wild bushes was key to my
delight in plants.
Secondly, I dedicate this work to the many unique and rare plants of the islands.
Lepidium oxycarpum (sharp-fruited pepper grass), a quarter-sized plant, is a State
Endangered species and a long-distance disjunct from its primary locality in California.
The photo on the following page, taken during thesis fieldwork, represents a new
population in Washington State. Before this, it was only known from one site. The entire
species exists in an area about the size of a large conference table and is likely one of the
rarest plants in Washington State. The wonder and curiosity of how this species arrived
on a single small island a thousand miles from the next known population drove most of
the inspiration for writing and working on this thesis. Such a species encapsulates all that
I appreciate and gain from studying plants and symbolizes all I have learned during my
time in Graduate school. May their stories inspire us to continue caring for the little green
things that fill our world.

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Lepidium oxycarpum (sharp-fruited pepper grass)

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“I take infinite pains to know the phenomena of the spring, for instance, thinking that I
have here the entire poem, and then, to my chagrin, I hear that it is but an imperfect copy
that I possess and have read, that my ancestors have torn out many of the first leaves and
grandest passages, and mutilated it in many places. I should not like to think that some
demigod had come before me and picked out some of the best of the stars. I wish to know
an entire heaven and an entire earth”
Henry David Thoreau, Walden

-

“Nature first, then theory. Or, better, nature and theory closely intertwined while you
throw all your intellectual capital at the subject. Love the organisms for themselves first,
then strain for general explanations, and with good fortune, discoveries will follow. If
they don’t, the love and pleasure will have been enough.”
-

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E. O. Wilson, The Naturalist

INTRODUCTION
Biodiversity loss is one of the most devastating aspects of the Anthropocene .
Loss occurs through 1) the extinction of species (Wilson, 1985; Pimm & Raven, 2000;
Barnosky et al., 2011; Valiente-Banuet et al., 2015; Briggs, 2017; Ceballos, Ehrlich &
Raven, 2020), 2) the decline of species abundance (Davies, 2011; Vogel, 2017; Leather,
2018; Goulson, 2019), 3) and the unraveling of ecological interactions (Valiente-Banuet
et al., 2015; Pérez-Méndez et al., 2016; Ulrich et al., 2020). These three kinds of
biodiversity loss negatively impact humanity, ecosystems, and the organisms themselves
(Tilman, 2000; Wilson, 2002; Cardinale et al., 2012; Cafaro & Primack, 2014). The
causes of biodiversity loss are well known and well documented and include habitat
destruction, invasive species, pollution, human overpopulation, and overharvesting
(Clavero & Garciaberthou, 2005; Liu et al., 2019; Ney-Nifle & Mangel, 2000; E. O.
Wilson, 2002; Young et al. 2016; Pyšek et al., 2020; Vitousek et al., 1997).
Islands are one of the most frequent places where scientists documented the
causes and consequences of biodiversity loss (Cook, Dawson & MacDonald, 2006; Sax
& Gaines, 2008; Quammen, 2012; Johnson et al., 2017), especially losses due to the
introduction of alien taxa and from human exploitation. Famous examples of species loss
on oceanic islands include the cascading influence of the brown tree snake on the
extinction of the endemic fauna of Guam, the introduction of mosquitos with malaria into
Hawaii, which facilitated the extinction of endemic birds, and the extinction of flightless
birds in New Zealand after settlement of the islands by the first Polynesians and later
colonization from Europeans (Engbring & Fritts, 1988; Quammen, 2012; Johnson et al.,
2017).

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Though plants on islands are more likely to go extinct than plants on mainlands
(Gray, 2019), there are fewer well-known examples, though Easter Island's extinction of
the Toromiro tree may be a notable exception (Maunder et al., 2000). However, since
1900, an average of 2.3 seed-bearing plants are going extinct each year, and islands have
the highest extinction rate. For example, since 1900, 79 plants have gone extinct on the
island of Hawaii (Humphreys et al., 2019).
The current and future impact of alien species on native plant species and
communities is a pressing concern. Alien species are responsible for at least 27% of
global documented plant extinctions (Bellard, Cassey & Blackburn, 2016). Currently,
alien plant species make up more than 20% of continental floras, and this number will
likely continue to increase. In the conterminous United States, alien species comprise
nearly 11% of the flora, and some states have up to 47% of their flora comprised of alien
taxa (Vitousek et al., 1997a). Washington State is no exception, as alien species comprise
30% of the state's flora1, and the state is in the upper 10th percentile of global hotspots of
established alien species (Pyšek et al., 2020).
This thesis explores how invasive and alien species and human development
affect the biodiversity of vascular plants in the San Juan Islands of Washington State, a
continental island archipelago in the Pacific Northwest of North America. The San Juan
Islands are an ideal locality to study biodiversity loss for three reasons. First, there are
disproportional numbers of species given the archipelago's land area. The plant species
found in the San Juan Islands represent 25% of the state's plant richness despite the land

1

https://biology.burke.washington.edu/herbarium/waflora/checklist.php

2

area of the archipelago comprising less than half a percent (0.26%) of the State (USDA
PLANTS database, 2018, WNPS, 2018). The archipelago is also a hotspot of alien
species, which comprise 34% of the flora (Atkinson & Sharpe, 2000).
Second, the high plant richness of the archipelago is likely related to the diversity
of habitats found across the archipelago, despite its latitude. Several reasons may explain
the high habitat diversity found in the archipelago, including being within the rain
shadow of the Olympic Mountains and the high topographic diversity found among and
within the islands. The Olympic Mountains and portions of Vancouver Island form
significant orographic barriers that strongly influence the climate in downwind areas.
Prevailing southwesterly winds are responsible for the major rainfall events in the region,
creating a pronounced rain shadow across extensive portions of the archipelago and
significantly buffers the region from dramatic precipitation events (Figure 1; LorentePlazas et al., 2018). The Olympic Mountains have likely significantly influenced the
archipelago's climate since at least the Miocene (~14 MYA), when the mountains uplifted
(Brandon, Roden-Tice & Garver, 1998). In conjunction with the stabilizing influence of
the Pacific maritime climate, it has likely been a climate refugia for species present when
the climate was cooler and drier during the Miocene (Pellatt, Hebda & Mathewes, 2001;
Retallack, 2001; Leopold et al., 2016).

3

Figure 1. Precipitation map of the Salish Sea, data produced by www.worldclim.org (Fick and
Hijmans 2017), red squares are drier (50mm a year), dark green are wetter (2120mm a year).

4

While topographic heterogeneity is important at large scales by producing rain
shadows, topography can have important influences at smaller scales too. Topographic
heterogeneity is also positively correlated with microhabitat diversity and species
diversity (Morelli et al., 2020). For example, in the San Juan Archipelago, Mount
Constitution on Orcas Island is a hotspot for elevational disjuncts (Atkinson & Sharpe,
2000). The cool north-facing slopes and small bog habitats of the mountain are home to
several taxa more common in mountain and boreal environments, such as the alpine
disjuncts Carex pauciflora, Saxifraga bronchialis, and Geum triflorum. The topographic
relief on Mount Constitution is likely one of the main reasons both xeric and mesic
species have been present on the mountain over the last 7,000 years through rapid
regional climatic changes (Sugimura et al., 2008; Leopold et al., 2016).
The third reason the San Juan Islands is an ideal study system is the configuration and
distribution of islands and how it relates to human use and density. Several large islands
served by State-sponsored ferries (San Juan, Lopez, Orcas, Shaw) comprise the center of
the archipelago. Surrounding these large islands are several hundred smaller islands–
many of which are uninhabited and either state parks or protected as refuges (Price, 2017;
Dunwiddie, 2018). The large ferry-served islands are visited by millions of people each
year (Whittaker, Shelby & Shelby, 2018) and serve as the pathway through which most
recreation occurs on the smaller islands.
Seabloom et al. (2006) found that alien species proceed into natural areas well before
the wave of human development. Given the well-known relationship between recreation
and alien species establishment (Jordan, 2000; Dickens, Gerhardt & Collinge, 2005;
Wells, Lauenroth & Bradford, 2012; Ballantyne, Gudes & Pickering, 2014; Marion et al.,

5

2016), such a configuration of large and small islands are an ideal study system for
understanding the influence of source-floras and rates of colonization after introduction.

THE IMPORTANCE OF BIOTIC HOMOGENIZATION

This thesis uses the concept of biotic homogenization as a lens through which to
study biodiversity loss. Understanding how floras are becoming simpler and more similar
through time is a core research topic in conservation biogeography (Olden, 2006). The
simplification of the earth's floras ("biotic homogenization") is driven by the combined
effects of the widespread introduction of alien plants into a region and the extinction and
extirpation of regional native species (Olden & Poff, 2003, p. 443). However, species
introductions and extinctions can have a lagged response, named invasion debt (Rouget et
al., 2016) and extinction debt (Hanski & Ovaskainen, 2002). While most biotic
homogenization research examines whether biotic homogenization is presently occurring
or has occurred, I found no studies yet that aim to explicitly assess how much
homogenization is likely to occur in an area in the future – a "homogenization debt."
Yet, there is sufficient theory to begin to postulate plausible scenarios for how
ecological communities are likely to change in the future, given knowledge of the known
flora, the factors that promote the colonization of alien species, and the factors that
increase the risk of extinctions – tools that the field of both biogeography and
conservation are well suited. The primary challenge to understanding what a
homogenization debt of an area could be are the well-known 'Darwinian' and 'Wallacean'
shortfalls – knowing what species are present in an area and how they are distributed
(Richardson & Whittaker, 2010; Ladle & Whittaker, 2011; Diniz-Filho et al., 2013).

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ADDRESSING THE DARWINIAN AND WALLACEAN SHORTFALLS

To address this first challenge, what species are present (Darwinian shortfall) and
how are they distributed (Wallacean shortfall), the tools and methods of floristic botany
were used (McLaughlin, 1994; Palmer, Wade & Neal, 1995). Floristic botany aims to
accurately describe the total number of species found in a focal region – from an
individual meadow to an entire biogeographic region such as the Pacific Northwest
(Hitchcock & Cronquist, 2018). A list and description of the species present is a
fundamental unit of biodiversity conservation (Wilson, 1999). Unfortunately, for vascular
plants, many areas of the planet are woefully inventoried. Botanical collecting is in
troubling decline (Prather et al., 2004a,b), despite the importance of herbarium
collections and natural history work in general for conservation (Shaffer, Fisher &
Davidson, 1998; Tewksbury et al., 2014; Greve et al., 2016; Nualart et al., 2017; Roberts
& Moat, 2022).
In the San Juan Islands, the first effort at a systematic vascular flora of the region
was made in 1985 by Atkinson and Sharpe. In addition, some work has been done for
mosses (Harpel, 1997). Before this work, plant collecting had been done sporadically
since the first collections made in 1892 by Louis F. Henderson on the Summit of Mount
Constitution. From 2005 to 2009, botanists associated with the Burke Herbarium began a
systematic effort to inventory the many small islands of the archipelago ("Floristic Atlas
of the San Juan Islands - WTU Herbarium," 2010). This effort continued in 2018 to
document the floras of the many small islands that became part of the new National
Monument (Dunwiddie, 2018). Work as part of this thesis continued in 2018, led by Peter

7

Dunwiddie, Peter Zika, and myself, to continue inventorying yet-to-be-visited islands,
better sample the larger islands in the archipelago, and revisit islands originally surveyed
in the initial 2005 - 2009 effort. The combined efforts of botanists over the last century
have led to at least 10,140 known collections across the islands. The majority (75%) have
occurred since the systematic efforts beginning in 2005 (Figure 2).

Figure 2. The number of herbarium collections of native and alien vascular plants within the San Juan
Island archipelago by decade.

Field inventories were supplemented by iNaturalist observations, past collecting
efforts databased in the Consortium of Pacific Northwest Herbaria, and species lists
compiled by local land management agencies, botanists, and other naturalists. By 2022,
there have now been 153 islands completely inventoried and five large islands (Orcas,
San Juan, Lopez, Shaw, and Blakely) extensively surveyed, for 158 total islands used as a
dataset for this thesis.
One of the troubling patterns in this broad-scale work is the steady increase in the
proportion of alien plant species found in the flora. For example, in 1985, Atkinson and
Sharpe recorded 829 taxa (34.1% alien species), and they updated their flora in 2000 and

8

recorded 970 species (36.1% alien). By 2022, there are now 1,010 documented taxa, and
38.7% is comprised of alien taxa, a pattern generally seen in the proportion of decadal
collections comprised of alien taxa (Figure 3).

Figure 3. The proportion of herbarium collections within the San Juan Island archipelago comprised
of alien taxa by decade.

Further, of the 156 islands, 145 (93%) had at least one alien species present, and the
islands that did not have alien taxa were all very small rocks with a flora comprised
solely of shoreline specialists well adapted to salt spray. Yet across all islands, alien taxa
comprised an average of 32% of an individual island's flora (CI90 = 2%), even though
island sizes ranged from 3 m2 (a small rock off Boulder Island) to 14,840 hectares (Orcas
Island). The stability and precision of this invasion estimate suggest alien species are
remarkably adept at colonizing islands regardless of their size. This ability has
implications for the long-term conservation and integrity of natural communities since
most islands are small, largely inaccessible, and not inhabited or visited by people.

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WHAT DRIVES THE COLONIZATION OF ALIEN SPECIES?

While understanding the factors that predict where an alien species will become
invasive continues to be a focus of intense research (Rejmanek & Richardson, 1996;
Milbau & Stout, 2008; van Kleunen, Weber & Fischer, 2010; Fei, Phillips & Shouse,
2014; van Kleunen, Dawson & Maurel, 2015; Klinerová, Tasevová & Dostál, 2018;
Nunez-Mir et al., 2019), general patterns remain elusive (Thompson & Davis, 2011).
Despite this, increasing evidence suggests the factors that influence the establishment of
alien species in new localities (Pyšek & Richardson, 2006; Milbau & Stout, 2008;
Richardson & Pyšek, 2012; Pyšek et al., 2015).
Key factors related to the establishment of alien species include their residence time
in a region, how long they have been associated with human settlement, their
evolutionary history, and specific plant traits. One of the most important aspects of
determining if an alien species becomes established is how long they have been in a new
focal region (Wilson et al., 2007; Sorte & Pyšek, 2009; Pyšek et al., 2015). Species that
have been present in a region longer are more likely to be naturalized and are more
frequent. Related to the concept of residence time is the idea that plants that have been
associated with human disturbance for a long time 'archeophytes,' are more likely to
establish that plants associated with more recent aspects of globalization 'neophytes'
(Pyšek, Richardson & Williamson, 2004; Preston, Pearman & Hall, 2004; Williamson et
al., 2008; Sorte & Pyšek, 2009). Other research has found that the specific plant families
of alien species, especially natural areas, are over-represented by members of Poaceae,
Fabaceae, and to a lesser extent Rosaceae (Daehler, 1998). Finally, several plant traits are

10

associated with the naturalization of alien plants, including clonality, nitrogen-fixation
ability, and whether an ornamental species (Milbau & Stout, 2008).
The above information on alien plants – their residence time in an area, whether they
are long-term associated with humanity, their evolutionary history, and plant traits are
readily, if tediously, available in the literature and herbarium records. When assessed in
concert with the well-known factors related to the extinction risk of native plants (narrow
geographic range, habitat specialization, and small population size; (Primack, 2014, pp.
157–173), modeling exercises can elucidate the potential plant community implications
of those future distributions. Such modeling exercises can be particularly effective if a
thorough effort has been made to catalog the number and distribution of native alien
species in a region.

POSITIONALITY ON ALIEN SPECIES AND CONSERVATION

In the harsh light of the Anthropocene, conservationists and others are
increasingly questioning the utility or importance of controlling alien species (Kareiva,
2011; Davis et al., 2011; Kareiva, Marvier & Lalasz, 2012; Thomas, 2013, 2017, 2019;
Orion, 2015). These thinkers suggest that the impact of alien species on natural
communities is overblown, management actions are cruel, discourse surrounding it is
racist, xenophobic, and the value judgments inherent in invasive species research are
unscientific (Colautti & MacIsaac, 2004; Sagoff, 2005; Warren, 2007; Larson, 2007;
Keulartz & van der Weele, 2009; Inglis, 2020). Some authors even suggest invasive
species will be the solution to the ecological crisis (Pearce, 2016). Despite these bold and
sometimes polemical claims, several authors have strongly refuted most of the core

11

claims of those denying the negative consequences of invasive species and highlighted
the various logical fallacies of critics of invasion biology and invasive species
management (Simberloff, 2003; Russell & Blackburn, 2017; Ricciardi & Ryan, 2018a,b;
Hayward et al., 2019; Callen et al., 2020), and the implicit and unarticulated values of
critics of traditional conservation (Doak et al., 2014; Hamilton, 2015; Baskin, 2015).
In particular, finding the ideal terminology for invasion biology has been
problematic (Ladle & Whittaker, 2011, pp. 26–28). I believe using neutral terminology as
proposed by Colautti and MacIssac (2004) obfuscates implicit values with their Stage I-V
categories, and I am unsatisfied with the clunky terminology of 'non-native', 'nonindigenous', 'potentially harmful species' (Inglis, 2020), or 'human symbionts' (Larson,
2005). While I acknowledge terms such as "exotic", "alien", and "invader" can have
painful and troubling social connotations, and not all alien species are invasive, such
parallelisms are, in many instances, unfounded, unfair, and problematic themselves
(Simberloff, 2003). I use the term alien to describe species not native to the San Juan
Island archipelago for two pragmatic reasons. First, biogeographic origin matters
(Buckley & Catford, 2016), and the primary definition of alien as an adjective is
"belonging or relating to another person, place or thing." The second reason is to have a
consistent terminology readily searchable in literature databases (Pyšek et al., 2004).
Finally, while some have tried to reconcile the invasive species debate, the value
differences likely remain intractable (O'Brien, 2006; Keulartz & van der Weele, 2009;
Frank et al., 2019; Coghlan & Cardilini, 2022). The differences may represent a case of
"non-overlapping magestiera" (Gould, 1999) and a continuation of the long-standing
"two cultures debate" (Snow & Snow, 1959) between rhetorical arguments based on the

12

post-modern literary tradition's conceptions of power, privilege, and 'contested
narratives' (Larson, 2005; Warren, 2007, 2021; Inglis, 2020), and those based on
empirical data and scientific reasoning demonstrating measurable harm to the natural
world, human health, and human economies (Clavero & Garciaberthou, 2005; Bellard,
Cassey & Blackburn, 2016; Frank et al., 2019; Blackburn, Bellard & Ricciardi, 2019;
Pyšek et al., 2020). Despite the siloed stalemate, there has also been some criticism of the
narratives put forth by invasive species skeptics from within the humanities. For example,
the work of Mastnak, Elyachar & Boellstorff (2014) on the idea of 'botanical
decolonialism' represents a forceful and compelling critique of the typical critical framing
of invasive species management as nativist, fascist and xenophobic.
I position myself towards thinkers that base their claims on empirical data and
scientific reasoning, especially when attempting to make claims about the material world
and what to do with it; broadly situating myself within the philosophical tradition of
'weak critical realism' (Carolan, 2005), especially when evaluating ideas in the context of
management choices (Mingers, 2006). I disagree with the claim that science is value-free
or that value-based reasoning is unscientific and fallacious (Colautti & MacIsaac, 2004;
Inglis, 2020). I believe that articulated values form the basis of several branches of
important inquiry, such as human health (Leung & Van Merode, 2019) and conservation
(Soulé, 1985; Meine, Soulé & Noss, 2006). These values are well articulated in David
Hume's moral philosophy (Cohon, 2018). Concerning alien species, I agree with the
values articulated by Buckley and Catford (2016) that considering the biogeographic
origin of species (i.e., accounting for alien species) is a key aspect of managing and
understanding natural communities. There is overwhelming evidence that alien species

13

have negative consequences on the communities they colonize, but biogeographic origin
alone should not be the sole basis for management decisions. Such values are generally
articulated by invasion and conservation biologists (Frank et al., 2019), despite strawman
arguments to the contrary.
Conservation biology is an explicitly value-laden field of inquiry that is often in
the middle of political and policy issues. Conservation science can be rhetorically easy to
dismiss if such values are not named and accounted for as objectively as possible. In one
of the seminal papers on conservation ethics, Callicott et al. (2000) created a conceptual
model of normative concepts in conservation. They divided these normative concepts into
two normative paradigms along a continuum from compositionalist to functionalist
values. Compositionalist norms emphasize the importance of species and species
assemblages. Compositionalist norms emphasize native versus alien species, view most
human actions through the lens of ecological degradation, and strongly prioritize the
protection and promotion of the native biodiversity of a region. Functionalist norms place
much less importance on the identity of species or species assemblages and more so on
ecological processes and ecosystem services.
This thesis strongly emphasizes compositionalist conservation norms (Callicott,
Crowder & Mumford, 2000; Ladle & Whittaker, 2011, pp. 31–32) and places the greatest
weight on preserving and protecting biota native to a given region. I have been strongly
shaped by the work of E. O. Wilson (Wilson, 1985, 1999, 2002), especially the sense of
biophilia he articulates (Wilson, 1984; Simaika & Samways, 2010). Further, I have been
strongly influenced by the ethics of the deep ecology movement, especially and belief in
the intrinsic value of the natural world (Soulé, 1985; Devall, 1988; Soulé & Lease, 1995;

14

Oelschlaeger, 2014; Smith, 2019; Callicott, 1984), and the belief that extinction is a
moral wrong (Cafaro & Primack, 2014). Thus, the primary goal of my conservation
practice is halting the extirpation and extinction of native species and regionally unique
communities.

ANALYTICAL FRAMEWORK

Weak critical realism prioritizes empirical ways of knowing and accepts the
difference between the claims to knowledge about an object or subject and the object or
subject themselves (Bhaskar, 1997). Such an approach is readily amenable to multimodel reasoning (Hilborn & Mangel, 1997; Anderson & Burnham, 2004) and Bayesian
inference (Mingers, 2006; McElreath, 2020). Multi-model reasoning posits there can be
several plausible explanations (i.e., models) that can effectively describe observed
phenomena (Hilborn & Mangel, 1997), which operationalizes the belief that knowledge
claims about things are separate from the things themselves. Bayesian reasoning can
evaluate the relative plausibility of knowledge claims (Wintle et al., 2003; Link &
Barker, 2006; Jarosz & Wiley, 2014; Navarro, 2020; Vehtari et al., 2021). Such an
analytical framework accepts that there is a 'real' world beyond the observer and that
there is always uncertainty in how much and what an observer can know about the 'real'.
In the context of species presence on islands, the historical contingency of
geology, climate, and non-replicability of the data make the epistemology of frequentist
statistics ("what is the likelihood of the hypothesis being true given a frequency
distribution of imagined replications of the data?") untenable since there are no replicates
of the San Juan Islands or replications of the contingent distribution of species present

15

among them. In contrast, the Bayesian conception of probability, 'what is the likelihood
of my hypothesis being true given the data?' is readily and intuitively interpretable
(Ellison, 2004; Kruschke, 2010; Wagenmakers et al., 2018).

CHAPTER SUMMARIES

The first chapter of this thesis explores the relationship between the invasion debt
of alien species, the extinction risk of native species, and how both could influence biotic
homogenization. Specifically, I examine what factors predict the current distribution of
alien species and, given time, how those distributions might change in the future. Using
the results of the modeling exercise, I postulate how biotic homogenization would change
in two human generations (by the year 2100) given the 90% percentile worst-case
scenario of alien species spread and the loss of all rare species (those found on fewer than
five islands). I posit such a question is conceptually significant because species diversity
is considered the bedrock of resiliency to massive ecosystem change (Wilson, 1999;
Cadotte & Davies, 2010; Richardson et al., 2012; Primack, 2014; Leitão et al., 2016), and
understanding the risk of invasive and alien plants to the native flora is fundamental to
their current and future conservation. This question is practically significant because
given spatially explicit information on where alien and native species are in the islands,
this work can help target which islands and species should be the focus of conservation,
restoration, and invasive species management and which native species should be the
focus of conservation actions.
The second chapter addresses the issue of biotic homogenization among some of
the most botanically unique small maritime meadow islands in the archipelago along the

16

southern edge of Lopez Island. These islands were originally surveyed in 2005-2009 and
have been well known by local botanists as one of the highest-density areas of rare plants
anywhere in the State. I was curious about the rate of change among islands completely
protected from human recreation and human use and if protected areas are protecting
natural communities.
Specifically, I was interested in how the rates of alien plant colonization and native
species extirpation were related to three growing conservation concerns in meadow
habitats across the region that can readily impact natural areas with no direct human
disturbance; invasive annual grasses, Canada geese, and deer. First, invasive annual
grasses can rapidly convert perennial grasslands into annual grasslands and increase fire
risk (Abatzoglou & Kolden, 2011; Davies, 2011; Balch et al., 2013; Garbowski et al.,
2021). Second, a population of non-native resident Canada geese introduced in the 1980s
has rapidly expanded across the San Juan and Gulf Islands, with strong evidence that they
are degrading meadow habitats at alarming rates (Best & Arcese, 2009; Isaac-Renton et
al., 2010; Bennett et al., 2011). Third, due to the changing social perceptions of hunting,
as well as the loss of primary predators in the islands, deer are rapidly exploding in
numbers across the islands, which are dramatically altering the structure and richness of
island plant communities (Martin, Arcese & Scheerder, 2011; Arcese et al., 2014).
Chapter two evaluates if the interaction of all three of these factors constitutes a potential
extinction vortex for native species (Gilpin, 1986). Conceptually, such work continues
the research agenda put forth by Seabloom et al. (2016). The analysis performed in
chapter two can inform future management across these biologically and ecologically
important islands.

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CHAPTER 1 – INVASION DEBT AND EXTINCTION RISK OF
VASCULAR PLANTS IN THE SAN JUAN ARCHIPELAGO
INTRODUCTION
Understanding how floras are becoming simpler and more similar through time is
a core research topic in conservation biogeography (Olden, 2006). The simplification of
the earth’s floras (“biotic homogenization”) is driven by the combined effects of the
widespread introduction of non-native plants into a region and the extinction and
extirpation of regional native species (Olden & Poff, 2003, p. 443). However, species
introductions and extinctions can have a lagged response, named invasion debt (Rouget et
al., 2016) and extinction debt (Hanski & Ovaskainen, 2002). While most biotic
homogenization research examines whether biotic homogenization is presently occurring,
I know no studies that explicitly assess how much future homogenization is likely to
occur; a “homogenization debt” (Purvis, 2003).
The idea of an “invasion debt” was coined by Seabloom et al. (2006) in a study of
the impact of alien species on the imperiled flora of California. The authors found that
many alien species had much smaller ranges than similar native species and argued that,
given time, alien plants would likely establish more widely across the state. The idea was
further developed by Essl et al. (2011). They found that many of the current problematic
invasive alien species were not recently introduced into a region but were legacies of
prior socio-economic activities. Yet a framework for measuring invasion debt did not
occur until the publication of Rouget et al. (2016).
Rouget et al. (2016) separated invasion debt into four components; introduction
debt, establishment debt, spread debt and impact debt. Introduction debt is the number of

18

species not in a focal region that are likely to become introduced. Establishment debt is
the number of species present in a focal region but not yet expanded beyond a limited
locality. Spread debt is the amount of area in a focal region that has yet to become
occupied by a given alien species. Finally, impact debt is the likely ecological and
economic cost of ‘paying’ the invasion debt.
Extinction debt is an older idea first introduced by Tilman et al. (1994), who
suggests that there can be a lag between the degradation or loss of habitat and the loss of
species. Rare species can be a particularly important component of extinction debt
because they are often already at the greatest risk of extinction (Hartley & Kunin, 2003).
Furthermore, the loss of rare species can be insidious because rare species can comprise a
disproportionate amount of a region’s diversity (Mi et al., 2012; Richardson et al., 2012;
Leitão et al., 2016; Thorn et al., 2020). While rare species may not comprise large
amounts of total cover, their importance may only become apparent during ecosystem
stress (Jain et al., 2014). For example, in oak meadows on Vancouver island, areas with
more rare species are more resistant to invasion and more resilient to environmental
stressors (MacDougall et al., 2013). The importance of rare species in times of ecosystem
stress may be due to the disproportionate amount of functional diversity found in rare
species (Mouillot et al., 2013; Leitão et al., 2016). Thus, rare species can act as
‘insurance’ during times of stress (Tilman & Downing, 1994; Chapin III, Torn & Tateno,
1996), and their loss can hasten degradation (MacDougall et al., 2013).
One important outcome of the interaction of both species invasions and extinction
is biotic homogenization, the non-random process of community change where common,
widespread species replace diverse assemblages of native taxa (Quammen, D, 1998;

19

McKinney & Lockwood, 1999). In their classic 1999 paper, McKinney and Lockwood
describe the 'winners' of biotic homogenization are rapidly dispersing habitat generalists
with large geographic ranges. Conversely, the 'losers' of biotic homogenization tend to
have the opposite species traits; they are small-ranged habitat specialists with slow
dispersal rates – typically the species endemic or unique to a region.
More recent research finds biotic homogenization causes highly skewed
taxonomic distributions (McKinney, 2002; Olden & Poff, 2003) For example, plant
species in Fabaceae and Poaceae disproportionately comprise the invasive and
introduced plant species of natural areas (Daehler, 1998). Thus, while alien plant species
tend to increase the local species richness of an area (Sax & Gaines, 2003), if they are all
closely related evolutionarily and have similar functional traits, such combinations of
species can decrease the resiliency of these novel plant assemblages to disturbances
(Olden et al., 2004). For example, since 1500 AD, the species richness of vascular plants
in Europe has increased by 1,621 species. Yet, phylogenetic alpha and beta diversity have
decreased because more closely related species comprise the resultant flora (Winter et al.,
2009).
Even the addition of a single alien species can rapidly homogenize a region’s
flora. In the Rhön UNESCO Biosphere reserve in Germany, the N-fixing sub-shrub
Lupinus polyphyllus, which was originally introduced to improve soil conditions, ended
up rapidly spreading and homogenizing the flora of the regionally unique alpine hay
meadows (Hansen et al., 2020). Many native species comprising the flora of the Rhön
cannot coexist in meadows dominated by L. polyphyllus, especially grasses, which did
not persist in invaded meadows. These invaded meadows were more homogenous in

20

species composition and functional traits, and present species leaned towards more
competitive species and species that could survive under cover of L. polyphyllus. In
Spain, the invasion of plants in the genus Carpobrotus reduced species and functional
richness, functional dispersion, and redundancy (Pino et al., 2009).
However, while the literature on current biotic homogenization has bloomed, I have yet
to find any literature assessing the idea of a homogenization debt. While the idea of a
“homogecene debt” was mentioned in passing in a book review (Purvis, 2003), the idea
has not been developed further in the literature. To develop the idea of a homogenization
debt and determine some potential mechanisms that could underly it, we use a
comprehensive floristic database of 156 islands from the San Juan Islands in the Pacific
Northwest of North America. Islands are particularly useful model systems in community
ecology because they have clearly defined boundaries and are replicated and isolated,
thus making delineating species pools more tractable (Warren et al., 2015).
The San Juan Islands in the Pacific Northwest of North America are an ideal
system to study these questions because it has many small islands that can be reasonably
censused. There have been extensive and systematic collecting efforts across the
archipelago since 2000. Further, the physical and socio-economic history of the San Juan
islands sets up an ideal experiment since the archipelago is reasonably isolated from the
mainland and most of the small islands cluster near the large islands. Most smaller
islands are uninhabited or used for recreation, with limited or no consistent human use. In
contrast, the large islands are inhabited by several thousand people and served by a state
ferry system that brings millions of people to the islands during the spring and summer
months. Thus, the large islands are ideal source locations for new alien plants, and being

21

a hub from which many then recreate the smaller islands, a reasonable source location
from which new invasions could occur.
In this chapter, I use a mixture of herbarium data and detailed and exhaustive
botanical inventory work to generate comprehensive species lists for 156 islands in the
San Juan archipelago and a flora for the whole archipelago. With this data, I examine
how the pool of likely introduced alien species, the pool of imperiled native species, and
where they are located influence the amount of current biotic homogenization and the
amount of homogenization possible in the future.
Since species diversity is considered the bedrock of resiliency to massive
ecosystem change (Tilman & Downing, 1994; Chapin III, Torn & Tateno, 1996;
MacDougall et al., 2013), understanding the risk of invasive and alien plants to the native
flora is fundamental to their current and future conservation. Because herbarium and atlas
data provide spatially explicit information on where alien and native species are, our
dataset provides a framework for regional conservation planning. Specifically, in the
islands, this work can help target which islands and species should be the focus of
conservation, restoration, and invasive species management and which native species
should be the focus of conservation actions.
METHODS
STUDY AREA

The study area encompasses 156 islands, 21% of the roughly 740 islands found
within San Juan, Whatcom, Skagit, and Island counties in Washington State (Figure 1).
The Washington mainland bounds the study region to the East, Boundary Pass and the

22

Georgia Strait to the North, the Haro Strait to the West, and the Strait of Juan De Fuca to
the West.
I considered islands to be areas of land surrounded by salt water at high tide. For islands
over 20 hectares, reported hectares were used. Sor smaller islands, perimeters were traced
using high-resolution google earth aerial imagery. The perimeter was considered to be
where terrestrial vascular plants could conceivably grow (excluding salt-spray rock
barrens). When difficult to discern, aerial images overlaid over a 2019 LiDAR of the
region was used. The total range of island sizes was between 2.9 m2 (Boulder Needle) to
14,840.96 hectares (Orcas Island).

23

Figure 1-1. The study area, islands that have been surveyed or censused are outlined in black.

24

COMPILING THE REGIONAL FLORA

LINES OF EVIDENCE

four lines of evidence was used to compile a list of all the species found in the
study area: herbarium records, iNaturalist records, species lists, and field surveys. For
herbarium records, the consortium of Pacific Northwest Herbaria website
(www.pnwherbaria.org) was queried for all collections within the study area based on a
traced polygon around all islands in the study area (Figure 1-2).

Figure 1-2. Delineation of the search query of the Consortium of Pacific Northwest Herbaria based on
a polygon of the study area.

Queries were also based on locality information that included “San Juan Islands” based
on a text search to capture potential records that had location errors and may not have
been captured in the polygon query. Once queried, all records were collated and reviewed
to create island-specific species lists. Species with only one herbarium record were re25

examined to determine the plausibility of identification and confirm the accuracy of
locality transcriptions. Because several of the earliest collections had broad locality
descriptions such as (“San Juan Islands” or “Wasp Islands”), these species were only
used to generate the possible regional species pool but not within the island-specific
analysis.
For iNaturalist records, photographs were examined for all records up to 2021 and
records were included if they were not of cultivated or planted individuals, were
definitively identifiable, and were not already documented from a vouchered herbarium
specimen. For species lists, all available lists published in the literature and by the
Washington Native Plant Society were compiled. Lists were also compiled from local
conservation organizations, land management agencies, and local botanists. These lists
were then collated by island, and new species were added if herbarium records did not
already capture them.
Finally, comprehensive floristic surveys were done of individual unsurveyed
islands and islands that have been under-botanized. Floristic surveys of smaller islands
involved multiple trained botanists visiting islands one to three times across the growing
season, and all habitats were censused for species. If habitats were not accessible on foot
(such as cliffs, impenetrable thickets and forests, and unwalkable rocky shorelines), they
were surveyed by boat with binoculars.
ESTIMATING TOTAL SPECIES RICHNESS

Since the number of observed species will always be less than the actual total
number of species in a flora, the Chao2 estimator (Chao, 1987) was used to determine the
minimum estimated number of native and alien species. Estimates were made within four

26

broad habitat types in the archipelago; open habitats (meadows, bald, and developed
land), forests (all forest types), wetland (including bogs, marshes, lakes, and ponds), and
shoreline habitats. Comparisons of the overall alien and native species pool can inform
broad patterns of invasion debt and extinction risk.
QUESTION 1: ARE THE DIFFERENCES IN SPECIES-AREA
CURVES BETWEEN ALIEN AND NATIVE TAXA?

Most broadly, alien species could pose a challenge to natural areas if they are less
limited than native species by island size and the associated ecological attributes related
to island size (habitat diversity, soil diversity, topography, etc.). If the same local
biogeographic factors largely constrain native and alien taxa in each of the four habitat
species pools, we would expect regressions of island area and richness would explain
similar levels of variance (R2) in both native and alien species within each species pool.
However, because island areas can have a minimal influence on species richness
up to a certain island area threshold (i.e., the small island effect; (Burns, Paul McHardy &
Pledger, 2009; Dengler, 2010; Wang, Chen & Millien, 2018; Chen et al., 2020; Matthews
& Rigal, 2021). I also used breakpoint regression to determine relationships between
island size and alien and native species richness (Matthews & Rigal, 2021). For islandarea models, semi-log function was used (Arrhenius, 1921), which is a generally more
accurate model than the log-log function for smaller islands (Panitsa et al., 2006).
In particular, the small island effect is likely driven by limitations in microhabitats
on the smallest islands (Chen et al., 2020). So, suppose alien taxa have fewer barriers to
dispersal and are more capable of colonizing and persisting in many habitats and
microhabitats. In that case, there should either be no or a very weak small island effect.

27

To determine differences between native and alien taxa for each nativity and habitat type
combination, five regression models were evaluated using multi-model inference (Table
1-1); 1) no small island effect (linear model), 2) a single threshold (small island effect
only), or 3) a two-threshold model (small and large island effect). To methods were used
for threshold models, continuous and left-horizontal models. Continuous threshold
models allow the slope but not intercept of a line to change at a given threshold, while a
left-horizontal model maintains a slope of zero before the first breakpoint (Dengler, 2010;
Matthews & Rigal, 2021).
Table 1-1. The six models used to assess the relationship between island size and species richness for
native and alien species in shoreline, open, forested, and wetland habitats. In each formulation, logS and
logA are the base10 log-transformation of species richness and island size, respectively, and the fitted
model parameters are ci (intercept), zi (slope), and Ti (threshold). Boolean logic expressions ( >, , &)
provide either 1 for true or 0 for false.
Model

Formulation

Linear

logS ~ c + zlogA

Continuous one-threshold

logS ~ c1 + (logA  T) z1logA + (logA > T) [z1T + z2(logA – T)]

Continuous two-threshold

logS ~ c1 + (logA  T) z1logA + (logA > T & logA  T2)
[z1T1 + z2 (logA – T1)] + (logA > T2) [z2 (T2 – T1) +z3 (logA – T2)]

Left-horizontal one-threshold

logS ~ c1 + (logA > T) z2 (logA – T)

Left-horizontal two-threshold

logS ~ c1 + (logA > T1 & logA  T2) [z2(logA – T1)] +
(logA > T2) [z2 (T2 – T1) + z3 (logA – T2)]

Once computed, R2 values for the same model for native and alien species
richness were compared. While it is inappropriate to compare R2 values of different
models describing the same response value due to the differences in the parameterization
of different models (Dengler, 2010), comparing the same model (and thus the same
parameterization) to both alien and native species richness should generally assess if the
same biogeographic processes are influencing alien and native species in the same way.

28

Specifically, if R2 values for a given model are higher for native species than for alien
species, biogeographic variables associated with size are more important for determining
species richness for native species than alien species.
Next, AICc and BIC information criteria were used to determine relative model
support and if the same general relationship between island size and richness occurs
within each nativity and habitat type combination. The debate over the proper
information criterion is extensive and beyond the scope of what is presented here.
Generally, AIC prioritizes model predictions, and BIC prioritizes correct functional
inference (For an introduction to the debate, see Aho et al. (2014) and references therein).
Here, models are considered to have sufficient support when both AIC and BIC converge
towards a similar top model. When information criteria do not agree, the relative
uncertainties between the two rankings for a given nativity and habitat are discussed.
Models that have AIC and BIC values with a   2 are considered as having equal
support (Harrison et al., 2018). Finally, plots of predicted threshold values were
compared to assess if models give reasonable estimates. Models were rejected that had
nonsensical threshold values or if regression lines crossed zero (predicting negative
species). Thus, it was considered plausible if the top model had the lowest AIC and BIC
values and provided ecologically defensible insight.
Finally, island size threshold values were compared between native and alien
species. Suppose alien species are less constrained by local biogeographic factors through
both increased ability to disperse into habitats and less likely to be extreme habitat
specialists. In that case, they should either 1) be less likely to have island size thresholds
if they are more capable of being present in even marginally sized habitats (Chen et al.,

29

2020), or 2) if a threshold is present, alien species should have a smaller island threshold
size than native species, for the same reason.

QUESTION 2: HOW AT RISK ARE IMPERILED SPECIES BY
INVASIVE SPECIES

Invasive species can disproportionately establish in habitats home to many
imperiled species (Stadler et al., 2000; Stohlgren, Barnett & Kartesz, 2003; Seabloom et
al., 2006). To determine if invasive species are associated with imperiled species in the
archipelago, Kendall rank correlations were performed (Whitlock & Schluter, 2015)
between imperiled and invasive species richness by island and habitat type. Species
found on fewer than five islands were considered imperiled because populations with
fewer than five occurrences are at higher risk of extinction (Hartley & Kunin, 2003).
Because there should be more species on large islands, invasive and imperiled species
richness were divided by island area before performing correlation analysis.
QUESTION 3: WHICH ALIEN PLANTS HAVE THE GREATEST
ESTABLISHMENT DEBT?
A core aspect of establishment debt is that the regional prevalence of given alien
taxa is related to residence time. In general, alien plants that have been in a region longer
will have dispersed to more sites than more recently established taxa (Sorte & Pyšek,
2009). Thus, establishment debt has three main components, how long were taxa in a
focal area, what are the plant traits of that species, and what is the number of potentially
suitable localities taxa could persist in (Rouget et al., 2016).
To investigate these three components of establishment debt, the question of how
strong the relationship is between invasion history, ecological attributes, and life history

30

of alien taxa and the proportion of islands an alien taxon is found on was examined
(Table 1-2).
This study considers five aspects of invasion history related to species prevalence,
four related to attributes of a given taxon, and one related to the degree of human impact
on an island. The four-taxon attributes are 1) the time since a taxon was first documented,
2) whether a taxon is an archaeophyte or neophyte, 3) how strong an invader is a taxon,
and 4) is the taxon an ornamental or horticultural. The fifth landscape attribute is an
ordinal score of the degree of human development on an island.
A strong correlation between residence time and prevalence would suggest that
recently established alien taxa are likely to spread in the future given enough time. A
weak or non-existent association with residence time would suggest other factors, such as
dispersal limitation or habitat limitation, could be more important and that the number of
alien taxa in the regional species pool, per se, is not a good measure of
establishment debt.
To assess the relationship between time since introduction and the current
distribution of alien taxa, herbarium data from the Consortium of Pacific Northwest
Herbaria was used to determine the year of the first record. It was then subtracted it from
2021 to get the time since first seen.
Because collections in the San Juan County have not been uniform throughout
time, a larger spatial area was used that included the largest metropolitan areas in the
region (Seattle, Washington to the South, Vancouver, BC to the North, Victoria, BC to
the West) to help mitigate some of the collection bias. Because for most of its EuroAmerican history, the San Juan’s has been a destination for people living in the region's

31

urban centers. So, while it is almost certain taxa have been present in a region longer than
the first herbarium record, earliest herbarium dates are assumed as a good enough proxy
for residence time.

32

Table 1-2. Candidate predictors of alien plant species frequency in the San Juan Island archipelago.
Component
Invasion History

Ecological

Life History

Factor
Time Since First
Seen

Data Type
Continuous

Description
The earliest year a given taxon was collected in the
Salish Sea region.

Hypothesis
Taxa present in the region for a longer time
will be more prevalent

Invasive Type

Categorical

Whether a given taxon is considered a Neophyte,
Archaeophyte, or Native in Europe (3 categories).

Invasive Status

Categorical

Ornamental

Binary

Whether a given taxon is invasive or non-invasive, and
an ecosystem transformer or not (4 categories).
Transformer status based on field experience,
literature, or if listed as allelopathic
Whether a given taxon was primarily introduced as an
ornamental plant (gardens or landscaping).

Taxa associated with human disturbance
(Archaeophytes/Neophytes) would be better
invaders than Native taxa.
Invasive transformers will be the most
common taxa, while non-invasive taxa will be
the least

Human Impact
Score
Island Size

Ordinal

A six-point score, see Table 1-3

Continuous

The smallest island a taxon is currently found on

Primary Habitat

Categorical

The primary habitat type a taxon grows in (4
categories; shoreline, open habitats, forest, or wetland).

Dispersal Type

Binary

Whether a taxon is a long or short disperser.

Life Span
Life Form

Categorical
Categorical

Clonality

Binary

Whether a taxon is an annual, biennial, or perennial.
Whether a taxon is a forb, graminoid, vine, or
shrub/tree.
Whether a taxon can reproduce vegetatively

Because ornamental plants make up a
disproportionate number of invasive species,
they should be more common.
Islands with a greater human impact score will
have more taxa
Taxa found on smaller islands are more likely
to be better dispersers and be found on more
islands
Species associated with open habitats will be
the most frequent

Long-distance dispersers will be more likely to
be present on an island

References
(Wilson et al., 2007; Sorte
& Pyšek, 2009; Pyšek et
al., 2015)
(Sorte & Pyšek, 2009;
Kalusová et al., 2013)
(Pyšek et al., 2004; Kalisz,
Kivlin & Bialic-Murphy,
2021; Hierro & Callaway,
2021)
(Dehnen-Schmutz et al.,
2007; van Kleunen et al.,
2018)
(Vitousek et al., 1997b)
(Aikio et al., 2020)

(Rejmánek, Richardson &
Pyšek, 2005; Richardson
& Pyšek, 2006; Kalusová
et al., 2013)
(Bennett et al., 2011)

33

In Europe, while determining the nativity of a taxon is challenging due to the
extensive history of human habitation and commerce, biogeographers created a general
framework of three broad categories: native, archaeophyte, and neophyte. Archaeophytes
are taxa with extensive archeological evidence for human association before 1500, the
general date of when global exploration began, while neophytes are taxa generally
associated with humans after this date (Preston, Pearman & Hall, 2004).
The general invasiveness of alien species in other parts of the world could help
predict how invasive they could be in the San Juan Archipelago. For each taxon, the
invasiveness status (invasive/naturalized) was determined as well whether the taxon is an
ecosystem transformer or not. Given the uncertainties of climate change, I had a liberal
consideration of the potential invasiveness of a taxon, and a species was considered
invasive if it is naturalized and recorded as invasive in at least one county in the United
States (Invasive Plant Atlas of the United States; Swearingen & Bargeron, 2016). The
effect that ecosystem transformers have on ecosystems is well established (Pyšek et al.,
2004; Fei, Phillips & Shouse, 2014; Coggan, Hayward & Gibb, 2018; Kalisz, Kivlin &
Bialic-Murphy, 2021; Hierro & Callaway, 2021), and native species will likely become
extirpated in invaded habitats if alien species transform ecosystems away from habitats
that are suitable for native species.
Ornamental garden plants are a common source of invasive species because many
are bred for fast-growing competitive traits (Dehnen-Schmutz et al., 2007; van Kleunen
et al., 2018). For example, in Ireland, ornamental species were more likely to become
established and invasive than other taxa (Milbau & Stout, 2008). However, given how
34

dry many of the natural habitats in the archipelago are, ornamental plants may not
comprise a significant proportion of the flora.
The effect of humans on ecosystems is well known and well documented
(Vitousek et al., 1997b; Maslin & Lewis, 2015; Young et al., 2016; DellaSala et al.,
2018), and alien species are generally thought to do well in human-dominated systems
(Vitousek et al., 1997a; McKinney & Lockwood, 1999; McKinney, 2005; Ellis &
Ramankutty, 2008; MacDougall et al., 2013; Thomas, 2017, 2019). Thus, alien species
are expected to be more frequent in areas with more human disturbance. Because
attempting to quantify human impact is multidimensional, an ordinal scale was created in
an attempt to create a simple measure of impact based on how accessible an island is if it
was settled or not, how developed it is, and how many people visit an island (Table 1-3).
Because species richness and colonization generally increase with area
(Arrhenius, 1921; MacArthur & Wilson, 1967; Aikio et al., 2020), I expect alien species
to be more probable on larger than smaller islands, especially because the larger islands
also have greater human impact and more potential habitats. There is strong evidence that
when habitats of a native community are more invadable when they match the source
habitats of alien plants (Rejmánek, Richardson & Pyšek, 2005; Richardson & Pyšek,
2006; Chytrý et al., 2008), especially when they are also disturbance-prone. Thus, the
archipelago’s coastal meadow habitats are more likely to be invaded because they are the
most similar to the meadow habitats of maritime Europe (Kalusová et al., 2013).
Finally, plant traits are often one of the most important factors determining how
well a species can colonize an island (Vittoz & Engler, 2007; Milbau & Stout, 2008;
Pyšek et al., 2015; Di Musciano et al., 2018; Junaedi & Mutaqien, 2018; Nunez-Mir et

35

al., 2019; Aikio et al., 2020). I chose to use broad life history traits – life span, life form,
clonality, and dispersal ability – because they are likely the most basic filters for whether
a species can disperse to an island and persist in a specific habitat. For example, shortlived species like annuals are more likely to become extirpated (Saar et al., 2012), while
clonal species are more likely to establish (Milbau & Stout, 2008; Aikio et al., 2020).
Table 1-3. Ordinal scale of human impact on islands in the San Juan archipelago
Human Impact Score
0

1

Description
An inaccessible island with no easily suitable landing location. Islands that
were never settled and currently have active restrictions against visiting.
Islands with a beach to land on but with no maintained recreation
infrastructure and were not historically settled by Europeans.
These islands either are publicly owned and have active restrictions
against visiting or are privately owned, but illegal visiting is still possible,
or limited visiting through permits is allowed.

36

2

Islands with a beach to land on but no maintained recreation
infrastructure, but way trails are present. Island may or may not have been
historically occupied or used but is currently unoccupied with low or
moderate visitation.

3

Islands with a beach to land on, recreation infrastructure present. Islands
are either day-use only or have limited and localized camping with limited
trails into the island's interior. Island may or may not have been
historically occupied or used but is currently unoccupied with moderate
visitation.

4

Islands with a beach to land on. Localized recreation infrastructure is
present with maintained trails, toilets, and multiple campsites. Mooring
may be present nearby, and islands are moderately to highly visited.
Islands with historic European settlement and development.

5

A currently inhabited island with residential development and either yearround or partly year-round occupancy.

6

Islands with a beach to land on. There is widespread recreation
infrastructure, with maintained trails, toilets, and multiple campsites.
Mooring is present nearby, and islands are heavily visited. Islands with
historic European settlement and development.

The published literature and field work were used to compile information on life
form, life duration, clonality, and dispersal range. Information provided within the Burke
herbarium (https://biology.burke.washington.edu/herbarium/imagecollection.php), the
electronic floristic atlas of British Columbia (https://linnet.geog.ubc.ca), and the online
flora of Britain and Ireland were used to determine life history traits
(https://plantatlas.brc.ac.uk/). For habitat preferences, a mixture of field observation,
notes from herbarium labels, and available literature were used and each taxon was coded
as likely to be found in shoreline, wetland, open and forested habitats. For dispersal
characteristics, the protocol of Bennett et al. (2013) was used to code species as a short or
long disperser.
Before running the first model, whether a given alien taxon was a failed
introduction was assessed becasue presence in a herbarium does not mean that a species
is currently extant in the archipelago. For each taxon, species not seen since 1985 were
considered a failed introduction. because the original 1985 publication of the Wild Plants
of the San Juan Islands was the first systematic and comprehensive flora of the region
(Atkinson & Sharpe, 2000).
Once all the above information was compiled ,two modeling exercises were
performed using generalized linear mixed models fit with Bayesian reasoning. The first
model assessed how invasion history, life history traits, and phylogeny influenced the
frequency of alien species across the islands. This model assessed the most important
species-level information to put into the second model, which assesses island-specific
occurrence probability based on species information, island area, and human impact.

37

Regression models were run using Bayesian inference using the package
brms (Bürkner, 2017). predictor variables were centered and standardized before running
each model. Each model was run with eight chains, each chain with 5,000 runs (2,500
warm-up), thinned to 100. The intercept was given a prior of mean = 0, standard
deviation = 0.5, and parameters a prior probability of mean = 0 and standard deviation of
1 based on prior predictive sampling (McElreath, 2020). Once run, all models were
assessed for chain convergence and if 𝑟̂ <1.03.
To compare model performance and determine variable importance, LOO
information criterion was used (LOOIC; Vehtari et al., 2021). Model weights were
assessed using the model-stacking approach (Yao et al., 2018). This approach weights the
model with the lowest posterior predictive error as more plausible. The relative variable
importance was then calculated for each predictor by summing the model weights for
each model that the predictor was present. To assess model performance,
compare_performance function in the performance R package was used (Lüdecke et al.,
2021). Finally, the model of island-specific occurrence probability was used to predict the
island-specific occurrence probability of each alien species in the year 2079 based on the
90% credible interval prediction. Thus, this prediction represents a plausible worst-case
scenario of alien species establishment.
QUESTION 4: HOMOGENIZATION DEBT?

To assess current and future homogenization, the Jaccard similarity was
calcualted for island pairs currently and in 2079 based on taxonomy (species) and
phylogeny using the framework provided by Baselga (2012). The change in pairwise
38

similarity was assessed using paired t-tests based on Bayes Factors using ggwithinstats()
function in the ggstatsplot package (Patil, 2021). All analysis was performed in R version
4.0.4. (R Core Team, 2021).

RESULTS
DESCRIBING THE REGIONAL FLORA

HOW MANY TAXA ARE IN THE FLORA?

Based on herbarium records, species lists, and field observations, there are 1,010
species (1,177 if including infra taxa) in the San Juan archipelago (Appendix 1). The
estimated minimum size of the actual flora based on the Chao2 estimate is 1,256 (CI95 =
1,134 to 1,575) species. Thus, between 64 to 89% of the San Juan archipelago flora is
currently known. Alien species make up 38% of the observed flora (385 species) and 42
to 47% of the estimated flora (Chao2 = 544, CI95 = 472 to 747 species).
When partitioned by broad habitat type (Figure 1-3), most species are associated
with open habitats (52%), followed by forested (21%), wetland (17%), and then shoreline
habitats (10%). Alien taxa dominate the flora of open habitats (62%) but are a much
smaller component of shoreline (25%), forest (16%), and wetland (7%) floras.

39

Figure 1-3. The number of observed (black) and estimated (grey) species across four habitat species
pools in the San Juan archipelago. Error bars represent 95% confidence intervals for the Chao2
species richness estimate.

HOW MUCH OF THE NATIVE FLORA IS RARE?
Rare species comprise 35% (349 species) of the archipelago’s flora (Table 1-4).
Most rare species are found only on one (110 species) or two (93) islands. Rare species
are mostly found in the two rarer habitats based on land area; wetland (n = 134) or open
(n = 98) habitats. These two habitats had most of the species of conservation concern (18
of 22 species), with open habitats also having the most species of conservation concern (n
= 14).
Table 1-4. Distribution of rare species across four habitat types found in the San Juan Archipelago

40

Habitat

Singleton

Doubleton

3-5 islands

WANHP

Total

% of Flora

Shoreline

9

8

14

3

34

43

Open

37

22

25

14

98

49.7

Forest

21

27

34

1

83

45.3

Wetland

43

36

51

4

134

83.8

HOW ESTABLISHED ARE ALIEN PLANTS?

Based on herbarium records, species lists, and field observations, there have been 385
alien plants recorded in the San Juan archipelago, and 90% of these species (n = 349) are
likely established in the archipelago (Figure 1-4). Open habitats have the most alien
species (n = 321), and wetland habitats have the fewest (10 species). Across all habitats,
invasive species comprise 70% of the alien flora and are more likely to become
established.
7 Invasive

6

30%

3 Naturalized

1

68%

21 Invasive

19

32%

10 Naturalized

9

71%

228 Invasive

29%

93 Naturalized

70%
10 Wetland

3%

31 Forest

385 taxa

83%
321 Open
6%

52%
23 Shoreline
48%

Likely Established

8%

209

349 taxa

83

12 Invasive

12

11 Naturalized

10

Figure 1-4. The status of 385 alien plant taxa documented within four habitat types found in the San
Juan Island archipelago, Washington State, USA. Values in boxes denote the number of taxa in each
category; percentages are based on the values from the preceding box. ‘Likely Established’ denote
taxa recorded in the archipelago and have been seen at least once since 1985.

41

CURRENT RISKS

In general, invasive alien species are more likely to be present when more rare
species are present, even after controlling for island area (Table 1-5). Therefore, rare
species associated with open and shoreline habitats have the highest pressure from
invasive alien species. In contrast, rare species associated with forest habitats are 53%
less likely than open habitats to have high invasive alien species pressure. Currently,
invasive alien species are not associated with high numbers of rare native species in
wetland habitats.
Table 1-5. Kendall rank correlation coefficients for the relationship between rare native species and
invasive alien species across all island habitats (All) and among four habitat types. For each habitat
type, correlations are only done on islands with rare native species present.

Habitat

Islands

tau

p

All

51

0.837

<0.0001

Shoreline

22

0.607

<0.0001

Open

37

0.883

<0.0001

Forest

24

0.499

0.0050

Wetland

12

-0.032

0.8886

BIOGEOGRAPHIC BARRIERS

Compared to a one-threshold or linear model, a two-threshold model had the
greatest support within each habitat and across all habitats (Table 1-6). While both AICc
and BIC generally selected the same top models, AICc was more likely to select the two-

42

threshold model that produced nonsensical predictions for the smallest and largest islands
(Appendix 2, Table A2-1).
Table 1-6. The top threshold model results for native and alien species across four habitats. ‘threshold
1’ and ‘threshold 2’ represent the threshold cut-off for their respective models (in hectares). For
models ranked by information criteria, see Appendix 2, Table A2-1.
R2

Native

Alien

Habitat

Native

Alien

threshold 1

threshold 2

threshold 1

threshold 2

Overall

0.94

0.86

0.048

1028.3

0.075

4509.5

Shoreline

0.78

0.7

0.002

1153.8

0.030

1637.3

Open

0.88

0.85

0.027

4700.3

0.065

4406.8

Forest

0.93

0.92

0.167

11806.7

1.714

6083.1

Wetland

0.98

0.79

47.003

13247.3

22.087

7658.2

When not separated by habitat types, island area generally explains 8% more
variation in native species richness than alien species richness (Figure 1-5, Table 1-6).
However, when not considering habitat types, there was a small island effect for both
native and alien species, but alien species had a slightly larger small island effect (0.08
hectares, 13 island difference; Figure 4).
The importance of habitat type becomes apparent when separately considering the
respective floras of the four broad habitat types. Across all habitat types and nativity,
there is generally a large island threshold between the largest small island (Sucia Island,
224 ha) and the smallest large island (Blakely island, 1,685 ha; Figure 1-6). Alien species
had a greater large island threshold (4509 hectares) correlated with the three large, highly
visited, ferry-served islands (Lopez, San Juan, and Orcas).

43

Figure 1-5. Island size and richness relationship between native (black) and alien (red) species. Dotted
lines represent island thresholds where the relationship between island area and species richness is
statistically different.

Among habitats, the difference in the influence of island size between native and
alien species was greater in wetland habitats (19% difference) and shoreline habitats (8%)
compared to open (3%) and forested habitats (1%). Small island effect thresholds were
generally smaller for native species than alien species (Figure 1-6), except for the alien
wetland flora, which had a smaller small island effect threshold (22 ha). However, the
slope of the ISAR was greater for native species across all habitats and thresholds except
the large island threshold for the alien open habitat flora (Figure 1-6).

44

Figure 1-6. Relationship of island size and richness between native (black) and alien (red) species
among four species pools; shoreline species, open (meadows and developed land), forests, and
wetlands. Dotted lines represent island thresholds where the relationship between island area and
species richness is statistically different.

45

FACTORS INFLUENCING ALIEN PLANT SPECIES FREQUENCY
In general, alien species attributes associated with invasiveness categories (residence
time, type, invasiveness status, and ornamental status) were more likely to be important
factors explaining species frequency across the San Juan archipelago compared to plant
traits (Table 1-7). Models that only considered the four invasiveness categories had the
best model support (w = 0.46; Appendix 2, Table A2-2). The invasion history categories
were used in the next modeling exercise of island-specific incidence probability.
Table 1-7. Importance of nine variables in models predicting the number of islands an alien species is
present. Importance values are the sum of model weights found in Table A2-1 in Appendix 2 and
represent the probability a given variable is in the most plausible model of the data.
Parameter

Type

Range

Importance

Residence Time

Continuous

0 – 141 years

0.70

Type

Categorical

Native/Archaeophyte/Neophyte

0.58

Status

Categorical

Invasive/InvasiveTransformer/

0.55

NonInvasive/NonInvasiveTransformer
Ornamental

Categorical

Yes/No

0.49

Life Span

Categorical

Annual/Biennial/Perennial

0.19

Clonal?

Categorical

Yes/No

0.10

Life Form

Categorical

Forb/Graminoid/Vine/Woody

0.09

Dispersal Type

Categorical

Short/Long

0.06

Primary Habitat

Categorical

Shoreline/Open/Forest/Wetland

0.08

Phylogeny had a modest influence on alien plant species frequency and explained
19% of the variance of the top model (Appendix2, Table A2-1). Within the phylogeny,
Clade explained most of the variance (68%), followed by Family (23%) and then Order
(9%).
46

Due to the long computation times (>14 hours), only the full model of islandspecific incidence was run. The full model had moderate support (R2Fixed = 0.29, R2Random
= 0.17, R2Full = 0.466). Island identity only explained 14% of the variance in random
effects, compared to phylogeny (86%). The relationship of phylogeny to island-specific
influence was roughly similar to the relationship of phylogeny to overall frequency.
Clade was most important (61%), followed by Family (19%) and Order (6%).
When considering island-specific occurrence, island area and human impact had
the largest positive effect on occurrence probability compared to invasion history (Figure
1-7). Alien species were 69% more probable on the largest island (83%) compared to the
smallest (14%) and were 55% more probable on the most impacted islands (70%)
compared to islands with no human impact (15%).
The residence time of an alien species had the greatest influence on the
occurrence probability compared to the other three invasiveness categories. Species that
had been in the archipelago longest (141 years) were 31% more likely to occur on an
island (34%) compared to the most recently arrived species (3%). The next most
important invasion history category was their invasive status. Invasive transformers had
the greatest occurrence probability (33%) and were 14% more likely to be on an island
than non-invasive alien species (19%). Species native to their source locality were nearly
twice as likely to be present on an island (30%) than either archaeophytes (15%) or
neophytes (13%). Finally, ornamental species were 10% less likely to occur on an island
(5%) than other alien species (15%).

47

Figure 1-7. Six predictors of island-specific alien species occurrence (probability of occurrence). In
panels A and C, shaded areas represent the 68% (dark grey) and 90% (light grey) credible intervals. In
panels B, D-F, bars represent 68% (black) and 90% (dark grey) credible intervals.

FUTURE HOMOGENIZATION

When predicting the worst-case distribution of alien species by 2079, alien
species are predicted to more than quadruple (average = 4.8x, sd = 2.6x) across islands,
and this increase could more than double the flora of each island (average = 2.2x, sd =
2.9x). Larger islands that are more heavily human-impacted are more likely to have
larger increases in the number of alien species (Figure 1-8).

48

Figure 1-8. Increases in future alien species richness between 2022 and worst-case projection for
2079. Arrows denote the projected number of added species between the two time periods. Arrows are
colored based on the human impact score of the island.

Based on the predicted worst-case increase in alien species and loss of rare
species, island floras will increase in taxonomic and phylogenetic similarity. In the
future, both taxonomic and phylogenetic similarity could increase by 20% across all
habitat types (Figure 1-9, Table 1-8). The flora of open habitats will have the greatest
increase in taxonomic similarity (24%) but a smaller increase in phylogenetic similarity
(12%).
Table 1-8. Bayes Factor t-test summary table.

Habitat
All
Habitats
Shoreline
Open
Forest
Wetland

Taxonomic
Difference
BF
0.20 (0.20, 0.21)
>1000

Difference
0.20 (0.19, 0.20)

BF
>1000

0.14 (0.14, 0.14)
0.24 (0.24, 0.25)
0.07 (0.06, 0.07)
0.07 (0.06, 0.09)

0.07 (0.07, 0.08)
0.12 (0.11, 0.12)
0.04 (0.04, 0.05)
0 (0, 0.02)

>1000
>1000
-180.97
-2.53

>1000
>1000
-491.35
-47.4

Phylogenetic

49

The predicted changes in similarity across other habitat floras are more modest,
and taxonomic similarity is more likely to increase than phylogenetic similarity.
Shoreline floras are expected to increase in taxonomic similarity by 14%, but only
phylogenetic similarity will only increase by 7%. Forest and wetland floras are predicted
to have the smallest changes in taxonomic similarity (7% each) and insignificant changes
in phylogenetic similarity (forest = 4%, wetland = 0%; Table 1-8).

Figure 1-9. Projected changes in the pairwise nestedness component of phylogenetic beta-diversity for
alien and native species between 2021 and 2179 (two human generations). Projections are based on
the loss of all rare native species and predicted worst-case increases in alien species richness.

DISCUSSION
OVERALL PATTERNS WITHIN THE FLORA

50

ESTIMATING THE SIZE OF THE FLORA
After the compilation of herbarium records, species lists, iNaturalist observations, and
field surveys, a significant number of new species were added to the known flora of the
San Juan archipelago. Atkinson and Sharpe (2000), the last comprehensive survey of the
archipelago’s flora, recorded 970 taxa, which added 141 taxa to their initial work first
published in 1985. The new taxa increased the proportion of alien species from 34% in
1985 to 36% by 2000. By 2022, there are 1,010 species (1,177 infra taxa), adding 207
taxa, 38% of which are alien plant species. While this is only an increase of 4% since
1985, if accounting for rates of unseen species, the actual proportion of the flora
comprised of alien species is between 42 and 47% and has likely increased by 8 to 13%.
When partitioned by nativity, there are fewer unseen native species (estimate = 13%,
uncertainty = 6 to 25%), than alien species (estimate = 28%, uncertainty = 16 to 47%).
While Chao2 estimates suggest significant uncertainty in the size of the unseen
flora (11 to 36% have yet to be seen), the upper confidence estimates for the number of
unseen species are likely improbable. Assessing the accuracy of Chao2 estimates is
difficult (Pitman & Jorgensen, 2002; Walther & Moore, 2005), and there are multiple
sources of uncertainty. A significant proportion of the native flora has not been seen since
1985 (185 species, 18%), and 55 of those species are only found on a single larger island.
The estimated unseen species will likely narrow if those species are instead considered
extirpated. Yet, at least one Lazarus species (a species thought to be extirpated but was
refound; Keith & Burgman, 2004), Brodiaea rosea, was found in recent surveys, even
though it was considered historical in Washington and had not been seen in 113 years
Figure 1-10. Brodiaea rosea (Indian Valley Brodiaea), a Lazarus taxon not seen since

51

1908 and thought to be extirpated in Washington State, rediscovered in 2021.. While
many of the smaller islands have been systematically surveyed, given the size of the
larger islands and how much of the larger islands are private property, it is still probable
many more ‘missing’ taxa are waiting to be rediscovered.

Figure 1-10. Brodiaea rosea (Indian Valley Brodiaea), a Lazarus taxon not seen since 1908 and
thought to be extirpated in Washington State, rediscovered in 2021.

While Chao2 estimates suggest significant uncertainty in the size of the unseen
flora (11 to 36% have yet to be seen), the upper confidence estimates for the number of
unseen species are likely improbable.
Another potential uncertainty source is related to whether the recently observed
alien taxa are waifs or not, and not including those taxa would also reduce the
uncertainty. This uncertainty is likely why the confidence bounds for alien taxa were so
52

broad (16 to 47% remaining to be seen). However, by having a more liberal cutoff for if a
species is in the flora, a sizable portion of unobserved alien species could be considered
as part of the establishment debt since these are species that could present, but not in
numbers large enough to have been seen by observers yet.

BROAD PATTERNS IN FLORA BASED ON HABITAT

The difference in the number of unseen species was also strongly influenced by
habitat type. The shoreline flora and forest flora are probably the most completely
inventoried (shoreline = 2-9% unseen, forest = 4-13% unseen). However, the shoreline
flora is likely the most species-poor (only 101 taxa, 25 alien) due to how extreme the
environment is and how few taxa are adapted to the high amounts of salt and sun
exposure in littoral environments (Atkinson & Sharpe, 2000). In particular, the alien
species that are most frequently found in shoreline habitats are common weeds in urban
hardscape environments – sidewalk cracks, parking lots, and rock walls [Hordeum sp,
Sagina sp, Rumex sp, Atriplex sp; (Frazee et al., 2019)]. Future work could further
evaluate the microhabitats of alien taxa that persist in urban environments to assess which
species are most likely to persist in shoreline habitats in natural areas.
The forest flora comprised generally regionally common taxa found on the
mainland (Hitchcock & Cronquist, 2018) and appears currently resistant to the
widespread invasion of alien plants. However, while temperate forests are often
considered invasion resistant, forests may just have longer time-lags between the
introduction of alien species and invasion (Essl, Mang & Moser, 2012). Furthermore, the

53

small proportion of alien species considered part of the forest flora also might be
somewhat underestimated. Alien species that are primarily found in open habitats are
present within open forests too – which are frequent habitat types within the archipelago
and were once much more common (MacDougall, Beckwith & Maslovat, 2004;
Bjorkman & Vellend, 2010; Dunwiddie et al., 2011; Arcese et al., 2018). Thus the
invasion debt likely present in forest habitats may only become paid if open forest
restoration becomes more frequent.
Wetland and open-habitat floras have more unseen species compared to shoreline
forests but likely for different reasons. The wetland flora has the smallest number and
proportion of alien species and the highest number of rare native species. Both facts are
likely due to how limited this habitat type is across the archipelago and how spatially
constrained they are to the largest islands. While some island wetland habitats are likely
never to be at much risk from invasive species (such as bogs), the high invasion debt for
other habitats, such as ponds, lakes, and freshwater wetlands, is more troubling. Wetland
habitats, especially on the larger islands, are probably under-sampled compared to
wetland habitats found on smaller islands due to the difficulty of surveying some of the
freshwater and wetland habitats on large islands. However, the number of unseen species
may be overestimated because there could simply be many singletons because freshwater
and wetland habitats are the rarest habitats in the archipelago. It is unknown how such
biogeographic patterns bias species estimates (Gotelli et al., 2009) and would be an
interesting and useful research problem.
The invasion debt of open habitats has largely been paid, and alien species
comprise most of the observed flora, and 18 to 26% of the alien flora remains to be seen.
54

The open coastal habitats found in the San Juan archipelago are very similar to the
coastal grasslands found in Europe, one of the most significant sources of alien species
(Kalusová et al., 2013). Native habitats that are similar to habitats from alien source
floras are more likely to be invaded by those source habitat species (Rejmánek,
Richardson & Pyšek, 2005; Richardson & Pyšek, 2006; Chytrý et al., 2008). In particular,
disturbance-prone habitats similar to alien source habitats are especially suspectable to
invasion (Kalusová et al., 2013). Not only are habitats similar between the archipelago
and maritime Europe, but the microclimate of meadow habitats of the San Juan islands is
very similar to summer-dry Mediterranean habitats, making them even more prone to
invasion (Kalusová et al., 2013). Meadow habitats in the archipelago hold 83% (n = 78)
of the alien species from the Mediterranean, and the most problematic invasive annual
grasses (Bromus, Vulpia, and Aira spp) and annual forbs (Hypochaeris glabra) are all
Mediterranean meadow and grassland species. Finally, when native habitats that match
alien habitats are also hotspots of diversity, they can also become hotspots of invasion
(Stadler et al., 2000; Seabloom et al., 2006; Kalusová et al., 2013).
The susceptibility of meadow habitats in the archipelago to invasion by alien
species is particularly insidious because the coastal meadow habitats also have a
disproportionate number of at-risk and rare species compared to other island habitats.
Meadow habitats also have many disjunct species associated with dry meadow habitats
east of the Cascades or California (Atkinson & Sharpe, 2000). Most of the regional
species of conservation concern (14 of 22 taxa) are associated with meadow habitats, and
the habitat itself is highly endangered (Bjorkman & Vellend, 2010; Dunwiddie & Bakker,
2011; Arcese et al., 2018). The archipelago’s meadows were likely maintained into the

55

modern period through indigenous management (Dunwiddie et al., 2011; Arcese et al.,
2014; Turner, 2014; Dick et al., 2022), and current disturbance-based restoration efforts
of burning and tree clearing are likely also facilitating alien species establishment.

ISLAND AREA AND HUMAN IMPACT

There is a small to modest difference in how alien species respond to increasing
island area compared to native species. Only larger islands (>200 ha) have a strong
positive relationship between island area and alien richness. However, it is difficult to
disentangle how much of this increase is due to the greater degree of human settlement
and visitation compared to island area alone. There is evidence that the dramatic increase
could be due to increased human presence and not area per se. For example, Cypress
Island (2227 ha) is a largely undeveloped island near Anacortes. It has nearly the same
number of alien species (n = 96) as Sucia island (223 ha, 106 alien species), a popular
State Park island for camping and visitation, which is 10x smaller in size. Another
example is San Juan Island (14840 ha), which is only 3% smaller than Orcas Island
(14258) but has 1.6x more alien species. This stark difference may be because San Juan
gets 2.4 more visitors than Orcas Island, and most visitors visit the islands to hike trails
and shorelines (Whittaker, Shelby & Shelby, 2018).
The influence of recreation on alien species introduction and establishment are
well known (Wells, Lauenroth & Bradford, 2012; Marion et al., 2016) and is likely the
primary driver of increased numbers of alien species on smaller islands that have
recreation compared to larger islands without much visitation. The difference due to
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recreation is likely why human impact score ‘5’ likely had a smaller influence on alien
species occurrence than score ‘6’ (Figure 1-7). Islands coded as ‘5’ were privately owned
residential islands and are visited by far fewer people than even moderately visited State
Park island. For example, Turn Island State Park is a popular 13.6ha forested island near
Friday Harbor that has 62% more alien species (68) than the similarly sized, privatelyowned forested Charles Island (13.3 ha, 42 species).

SPECIES CHARACTERISTICS AND ESTABLISHMENT

The importance of human impact in facilitating alien species occurrence is more
troubling because residence time is the most important variable compared to life history
in determining how frequent a species is throughout the archipelago. However, some life
history traits may correlate to residence time, even though there was no strong
collinearity between life history predictors. For example, long-dispersing annual forbs
and grasses were the first to establish in the region compared to short-dispersing
perennials (Appendix 2, Figures A2-1 to A2-5), and alien annual grasses are the most
common commonly found taxa in the flora.
Besides residence time, invasiveness in other areas in the country and being
native to the source region increased the frequency of alien species in the archipelago.
However, it may be difficult to tease apart the influence of residence time from a species
being an invasive ecosystem transformer because transformers are generally the first
species to establish in the area (Appendix 2, figure A2-5). The fact that archaeophytes
and neophytes were less frequent than alien species that are native in their home range is

57

likely further evidence confirming that similar habitats across continents are capable of
sharing many species when dispersal barriers are removed (Rejmánek, Richardson &
Pyšek, 2005; Richardson & Pyšek, 2006; Kalusová et al., 2013).

A HOMOGENIZATION DEBT?

Residence time and human impact primarily drive the number of alien species
found in the archipelago. There is likely a significant homogenization debt waiting to be
paid in the next few human generations. In the future, islands with the greatest human
impacts now could have nearly four times more species, and these species will cause both
taxonomic and phylogenetic homogenization. The greatest rates of homogenization will
be in meadow habitats that also have the most at-risk species.
Most of the recently introduced alien taxa are associated with the largest ferryserved islands. These taxa represent an establishment debt for the rest of the archipelago.
Their overall impact will also depend upon how much area is available to invade in
various island habitats (spread debt). Most of these recently introduced alien taxa,
regardless of habitat, will likely establish, but the effect this will have on future
homogenization rates will depend on the habitat. Shoreline and open habitats (meadows
and open forests) will have the greatest homogenization rates, while forests and wetlands
are the least likely to become dramatically homogenized in the future.
Because this study does not assess cover as well as incidence, the actual rates of
homogenization in the future will likely be higher. While focusing on species presence is
easier to do analytically and logistically, the dominance of a species in a habitat is
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incredibly important. If alien species become the primary common species, the realized
homogenization will likely be much greater (Bühler & Roth, 2011), even if rare species
persist in small microsites.
Forests and wetlands are not expected to become more homogenized in the future.
Many alien species that invade both habitats are neophytes (Chytrý et al., 2008) and are
not strong disperses across the islands regardless of residence time. However, I did not
consider the introduction debt. There are likely many alien taxa found on the Washington
State and British Columbia mainland that could persist in the islands but have not been
detected in the region yet. Future work could use the modeling exercises performed in
this study to evaluate how likely alien taxa found outside the archipelago (mainland,
bioregion, continent, world) could establish within the archipelago. Thus, the
homogenization debt predicted in this study should be considered a “minimum” estimate.

CONCLUSION

This chapter proposed a framework for evaluating conservation needs in
the future. I attempted to demonstrate how information-rich species lists and
herbarium records are and how novel and informative patterns can emerge when
paired with hypotheses and ecological theory. Despite being the basic information
of conservation science, accurate lists of the number and distribution of species
can be difficult and very time consuming to produce. However, such efforts are
worth it. Given the increasing amount of ecological information about species
found in published literature and available online in resources like herbaria and

59

species atlases, such lists can examine pressing questions important to
conservation.
The San Juan archipelago is a region with one of the greatest proportions
of alien taxa globally (Pyšek et al., 2020) and is also a hotspot of regional plant
diversity. Many millions of people visit the archipelago every year from across
the world and likely are the source of most of the recent introductions of new
alien taxa. The climate and habitats of the archipelago promote high levels of
regional native plant diversity and are also like the source regions of alien species
from European and Mediterranean source habitats. Thus, habitats with the most
imperiled species are also habitats that have the greatest invasive species pressure,
similar to patterns found in California (Seabloom et al., 2006).
Without intervention, these imperiled habitats are likely to experience
significant biotic homogenization. However, because the most imperiled habitats
in the archipelago, meadows and open forests, are dependent upon disturbance,
interventions are likely to facilitate continued alien species establishment (Chytrý
et al., 2008; Kalusová et al., 2013). Further, these imperiled habitats are some of
the most popular hiking and camping destinations in the region and are a vital
component of the regional economy (Whittaker, Shelby & Shelby, 2018). Many
millions of people visit the archipelago every year from across the world and
likely are the source of most of the recent introductions of new alien taxa. Finding
a solution to the conundrum of restoring these habitats, reducing alien species
pressures, and managing recreation may represent a "wicked problem”(DeFries
& Nagendra, 2017), with no straightforward or tractable management solution.
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However, managing the seemingly disparate goals of nature conservation and
human recreation is a well-known issue in park management (Anderson, Lime &
Wang, 1998; Wright, 2003). Future work engaging in this discipline may be a
fruitful next step.

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CHAPTER 2 – ASSESSING FLORISTIC CHANGE ON SMALL
ISLANDS IN THE SOUTHERN SAN JUAN ARCHIPELAGO
INTRODUCTION
THE HOMOGECENE?

Global commerce and its associated economic development across the earth is
removing natural biogeographical barriers to species distributions and causing massive
changes to ecosystems (Richardson & Pyšek, 2012). The removal of dispersal barriers
and the related loss and change to natural habitats is causing floras across the world to
lose their biogeographical uniqueness (Olden & Poff, 2003; La Sorte, McKinney &
Pyšek, 2007; Yang et al., 2021), a process also known as biotic homogenization
(McKinney & Lockwood, 1999). Due to the ubiquity of biotic homogenization across
taxons, this current period of the Anthropocene is being dubbed the “Homogecene”
(Rejmánek, 2002) or the “New Pangea” (McKinney, 2005).
While biotic homogenization is generally due to the combined effects of both
extirpations and introductions (McKinney & Lockwood, 1999), there are varied pathways
and patterns of extirpations and introductions that could lead to either biotic
homogenization or biotic differentiation (Olden & Poff, 2003). Further, biotic
homogenization or differentiation patterns can happen at several levels of biotic
organization: taxonomic, phylogenetic, or functional (Olden et al., 2004). Thus,
ecologists increasingly urge conservationists to look beyond species richness alone when
measuring the impact of human disturbance and also incorporate metrics relating to the
62

composition of species, their phylogenetic history, evolutionary uniqueness, and their
trait diversity (Winter et al., 2009; Cadotte & Davies, 2010, 2016; Tucker et al., 2017;
Hillebrand et al., 2018). For example, plant colonization generally outpaces plant
extirpations on islands, and overall plant species richness has generally doubled (Sax &
Gaines, 2008). Because many invasive and alien plant species that invade natural areas
are from only a few plant families – primarily Poaceae and Fabaceae (Daehler, 1998),
such species additions could cause floras to become simple and highly redundant not due
to the loss of unique plant but the addition of many closely related and broadly
distributed plants.
In this chapter, I examine four broad and inter-related questions.
1) Is there a directional change in plant community diversity across islands, and
how much is due to invasive species compared to island area?
2) Are changes in community diversity due to the differential colonization and
extirpation of alien and native species?
3) Are these changes leading to biotic homogenization?
4) Can the patterns found in questions 1-3 be detected in models of individual
species persistence on islands?
ISLANDS AT RISK
The San Juan archipelago islands are one of the jewels of Washington’s plant
biodiversity. Despite only accounting for 0.26% of Washington’s landmass, botanists can
find 30% of Washington’s native plants within the archipelago. Within the archipelago,
the hundreds of small islets are a particularly important component of the region’s
biodiversity. For example, the small, dry, and windswept islets on the south end of Lopez
63

Island are home to unique, globally rare coastal meadows. These meadows have
populations of globally rare species such as Castilleja victoriae, regionally rare species
such as Aphyllon californicum, and Ranunculus californicus, as well as unique disjunct
populations of Opuntia fragilis, Oxytropis campestris var. spicata, and Shepherdia
canadensis. There are few places in Washington where a botanist could encounter so
many rare and unique species in such a small area.

Yet, while these islands are highly-protected as conservation lands by the State or
Federal government, there are several reasons to believe they are at considerable risk of
losing their botanical uniqueness. These risks include the synergistic impact of extended
drought, the invasion of weedy species, the inherent demographic risks of small
populations on small islands, an increase in browsing and disturbance due to the growth
and spread of an introduced population of Canada geese, over abundant black-tailed deer,
and the regional rarity of many native species that comprise these unique plant
assemblages (Table 2-1).

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Table 2-1. Summary of Overall demographic and ecological risk of the eight islands in the study. Overall Risk is the hypothesized risk of homogenization
based upon three demographic risk factors and nine ecological risk factors. The demographic risk factors include: 1) the number of native species per
island that are regionally rare in the San Juan Islands2 2) the number of “species of concern”3 per island, and 3) the number of native species with small
populations4. The nine ecological risk factors include the presence of nesting Canada geese, mule deer, and seven problematic invasive weeds. For the
seven weeds, the recorded cover class value from 2005-2009 is provided. * islands that are comprised of a cluster of rocks.
Island
Risk Factor

Component

Goose
Island

Aleck
Rock

Overall Risk
Demographic

Castle
Island

Iceberg
Island

Boulder
Island

Flint
Beach
Island

High
Disjunct

3

1) Regionally rare spp

2

2) WNAP spp of concern

1

3) Native spp w/ small
populations

27

Canada Geese

Nesting

5

1
8

Blind
Island

Long*
Island
Rocks

Moderate

Swirl*
Rocks
Low

5

3

9

8

6

5

1

11

4

8

7

7

8

3

2

2

1

2

2

2

1

16

12

8

7

9

7

4

Nesting

Nesting

Nesting

Present

Present
R/F

Ecological1

Mule Deer
Annual Bromus spp

C/F

Vulpia spp
Hordeum murinum
Rubus armeniacus

C

F/LC

C

A / LC

NR

O

O

O

F

R

O

LC

O

R

O

NR

C

A

R

1

NR = present but abundance not recorded, R = rare, O = occasional, LC = locally common, F = frequent, C = common; 2Defined as species that have been recorded on 3 or fewer islands; 3As
defined by the Washington Natural Areas Program; 4 Defined as species that were assigned an ordinal cover of “rare” in the 2005-09 surveys

65

ABIOTIC STRESSORS
The small islets and rocks on the south end of Lopez are some of the driest and
most exposed islands in the archipelago. The average rainfall during the growing season
(March – June) is about half an inch less (0.50”) than the rest of the archipelago (PRISM
Climate Group). In addition to low rainfall, most islands are dominated by southerly
aspects and exposed to the high winds and salt spray from the Strait of Juan de Fuca and
Rosario Strait (Figure 2-1).

Figure 2-1. The dry southern face of Boulder Island in early June.

In combination with the harsh conditions on these islands, growing season
precipitation has been consecutively below average during the past five of the last ten
years, and rainfall ranged from 10% (2018) to 43% (2015) below average
(climatetoolbox.org ).

66

The combination of naturally harsh island conditions and repeated summer
drought has likely caused considerable stress to most plant species growing on these
islands. For example, rain is important for moving salt through soil (Mulder et al., 2011),
and extended periods of drought during the growing season may exacerbate salt stress.
Further, many small islands are rocky habitats that amplify solar radiation and likely
multiply the stress of water-limitation by increasing temperature and evapotranspiration
(Atkinson & Sharpe, 2000). Since water scarcity also increases the likelihood of
competitive interactions within and among plant species (Kijne, 2006; Tlidi et al., 2020),
considerable population reductions and extirpations have likely occurred since initial
island surveys in 2005 – 2009.

INVASIVE SPECIES STRESSORS

Invasive alien species can pose significant threats to natural plant communities,
even in protected areas with little human impact (Foxcroft et al., 2017). Seabloom et al.
(2006) found that invasive and weedy alien species established in natural areas well
beyond areas of intense human settlement disproportionally impact areas with high
densities of imperiled species.
Several invasive exotic plant species initially detected on these islands have likely
increased the risk of biotic homogenization during the past decade. First, drought-adapted
invasive annual grasses have likely benefited from the wet winters and dry, droughty
summers of the past few years (Abatzoglou & Kolden, 2011). The invasive annual
grasses found in the San Juans Vulpia (V. myuros, V. bromoides), Bromus (B. hordeacus,
B. sterilis, B. tectorum, B. rigidus) are likely more competitive than associated species

67

because they are winter annuals that typically complete their life cycle by late spring (for
an example with B. tectorum, see Garbowski et al., 2021). These annual grasses' different
phenology makes them less likely to be impacted by extended summer droughts than
native taxa, which typically reproduce and complete their life cycles later in the growing
season.
Another potential risk of invasive annual grasses is through altering fire regimes
by increasing fire intervals and converting natural areas to near-permanent annual
grasslands (D’Antonio & Vitousek, 1992; Balch et al., 2013; Fusco et al., 2019). An
increased risk of unplanned fire could lead to species extinctions, especially for plant
populations that are already small, not adapted to frequent fire disturbance, or if the fire
intensity is greater than typically experienced by a species (Bloom et al., 2018). The
invasive shrub, Rubus bifrons, is another species that could negatively impact native plant
diversity on these islands. At nearby American Camp on San Juan Island, R. bifrons has
converted significant portions of coastal meadow and bluff habitats into dense shrublands
where few other species can persist (Martin & Martin 2021).
Since many native plant species persist in small soil pockets on rocky islets that
may only span a few square meters per island, even one established shrub could eliminate
entire meadow habitats on some of the smallest islands. R. bifrons establishment could
also hasten and facilitate the rapid conversion of meadow habitats to shrub thickets when
other genera like Sympocarpus and Rosa are present.
A second threat to the native flora of these islands originated with the introduction
of two non-native subspecies of Canada geese to Victoria, BC, and the San Juans in the
1980s (Figure 2-2). These have spread widely throughout the San Juan and Gulf Islands
68

Figure 2-2. Left Panel: a rocky outcrop heavily impacted by Canada geese (Branta canadensis) loafing,
Male geese stand on prominent locations while guarding nest sites. These sites largely devoid of plant life
except invasive annual grass, weedy annual forbs and dominated by geese feces. Right Panel: A typical
disturbance around a goose nest. Note the sparse vegetation, upturned soil and abundant feces.

and now nest on many smaller islands where they are not disturbed by human visitors and
many predators. Unlike the native Canada geese, that were largely migratory and
relatively uncommon, the year-round presence of these resident birds is rapidly changing
the flora of islands where they nest in abundance through herbivory, nutrient and alien
species introductions, and nest building (Bennett et al., 2011; Best & Arcese, 2009; Dawe
& Stewart, 2010; Isaac-Renton et al., 2010).
The threat of invasive species amplifies the risks of island extirpations due to
small island size (Wilcove et al., 1998), prone to extinction and colonization events
(MacArthur & Wilson, 1967). Global and regional rarity compounds the risks of small
populations of plants living on small islands. For example, in Washington, the globally
69

rare species Castilleja victoriae only grows in an area of a few tens of square meters on a
single island in the San Juans. Several other species have regionally disjunct distributions
(Oxytropsis campestris var. spicata, Ranunculus californicus). They are only known from
a few localities in the San Juans with small to medium-sized populations. Finally, other
native taxa have larger regional distributions but are only present as a single or a few
individuals, making them the most likely to have become extirpated over the past decade.
Some of these species exhibit traits (low stature, lack of clonal growth, absence of
substantial storage organs like bulbs or corms) that may make them more susceptible to
population declines or extinction (Saar et al., 2012).

METHODS
LOCATION

Seven islands (Boulder, Iceberg, Flint Beach, Goose, Castle, and Blind Island,
Blind Island South) and two island clusters (Swirl Rocks and Long Island Rocks) were
revisited that were originally surveyed between 2005 and 2009 by Peter Dunwiddie,
David Giblin, and others (Figure 2-3).

70

Figure 2-3. Map of surveyed Islands along the southern shores of Lopez Island, Washington USA.

FIELD SAMPLING

The field sampling methodology follows the protocol used on previous island
surveys (Dunwiddie 2018). During the original surveys, botanists visited an island up to
three times in early spring, summer and fall and looked for plants until they thoroughly
examined all habitat types, and the rate of species detection dramatically slowed.
Inaccessible habitats such as cliff faces were surveyed with binoculars by boat. The field
protocol involves multiple trained botanists identifying all vascular plant species present
on an island in the field or collecting samples of unknown plants to identify later. All
identified species were given an ordinal cover class value based on a six-point range from
rare to abundant.

71

In addition to identifying vascular plant species, all Canada goose nests were
tallied, and each island was given a three-point ordinal assessment of goose impact based
on the number of nests found, how much of the island they were found across, and what
proportion of the island was impacted by forage and loafing behavior.

ANALYSIS

I examined five questions to determine if native plant species are declining and if
these declines lead to biotic homogenization.
5) Do four components of plant community diversity (nativity,
biogeographically-weighted evolutionary distinctiveness, evolutionary
importance, and functional richness) within and across the sampled islands
change between the initial surveys and 2021?
6) Do native species become extirpated from islands more than alien species, and
are they balanced by colonization?
7) How do area, Canada geese, deer herbivory, and invasive annual grass
influence rates of community change?
8) Do the changes in species composition lead to biotic homogenization across
the sample islands?
9) How does island area, the impact of invasive species, plant traits, plant
nativity, and phylogenetic relatedness influence the probability that a species
will go extinct from an island?

72

To first visualize changes in community composition (based on the ordinal cover
of species and presence/absence) through time, non-metric multidimensional scaling
(NMDS) ordination was used (McCune, Grace & Urban, 2002). Next, differences in
composition were visualized by successional arrows to display the direction and
magnitude of change. Finally, ordinations were performed using the vegan package
(Oksanen et al., 2013).
The most basic aspect of biotic homogenization is the loss of native species and
their replacement by alien species. Thus, the proportion of the total flora comprised of
native species (nativity) was calculated for each island. A more nuanced measure of
biotic homogenization evaluates the phylogenetic diversity of a flora. To assess the
phylogenetic homogenization of an island’s flora evolutionary distinctiveness(Faith &
Baker, 2006; Redding & Mooers, 2006; Cadotte & Davies, 2010) and evolutionary
importance were calculated. Evolutionary distinctiveness measures the number of
ancestral lineage branch splits within a given taxon’s history – the fewer splits, the more
distinct (Redding & Mooers, 2006). However, since a key aspect of biotic
homogenization is the replacement of communities by widespread generalists, native
species' evolutionary distinctiveness values (Native BED) were weighted by their
regional incidence across 156 islands (Dunwiddie 2018, Chapter One).
To generate a phylogenetic tree, the R package VPhylomaker was used (Jin &
Qian, 2019) based upon the backbone phylogenetic tree of seed plants created by Smith
and Brown (2018). Before calculation, the list of all species found within the San Juan
archipelago (Chapter One) was first prepared to be consilient with the Smith and Brown
tree. First, all infra-taxa were lumped to the species level, and then species names were

73

converted to the accepted name found in The Plant List (www.theplantlist.org). Once the
phylogenetic tree of the San Juan archipelago flora was created, the evol.distinct()
command in the picante R package was used to calculate the evolutionary distinctiveness
of each species based upon the fair proportions algorithm (Isaac et al., 2007).
Because the loss of phylogenetic diversity could also lead to the loss of
functional diversity (Schuldt et al., 2014; Arnan, Cerdá & Retana, 2017), I also examined
the change in functional richness based on categorical traits related to dispersal (long or
short disperser), life form [forb, grass, shrub, tree, or ancient plant (conifer, fern,
lycophyte)] and persistence traits (clonality, annual/perennial, presence of storage
organs). Functional traits were compiled from field experience or published literature
(Hitchcock & Cronquist, 2018, www.try-db.org). Seed dispersal traits were lumped into
either short or long dispersers following methods in Bennett et al. (2013). Finally, to
determine if changes in nativity, evolutionary distinctiveness, importance, and functional
richness were due to proportional losses in native species, I compared the rates of island
extirpations relative to colonizations for both native and alien plants. Paired t-tests using
Bayesian inference (Bayes Factors) were performed to assess if the four community
components changed between the initial 2005-2009 surveys and 2021 using the
ggwithinstats() function in the ggstatsplot package (Patil, 2021).
Regression analysis using Bayesian inference was used to determine how much
of the island-specific change in community composition was related to island area, deer
and goose herbivory, and invasive alien grass on the amount of island-specific change
between periods. Island areas were determined using aerial imagery to measure the
maximum area capable of supporting vascular plants. If islands were small enough, the
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circumference was mapped using handheld GPS. During visits, each island was given an
ordinal goose-deer impact score (DG) based on four values; no impact (0), low impact
(1), moderate impact (2), and large impact (3). Impact assessments were based on
whether both deer and geese sign was present on an island and how localized the impacts
were. Low impact islands had either a highly localized goose presence (one or fewer
nests, with limited evidence of loafing damage) or limited deer browse. Moderately
impacted islands had at least several goose nests and evidence of several patches of
localized goose damage. Moderately impacted islands also had evidence of several deer
(multiple deer pellet piles, tracks of multiple sizes, extensively browsed shrubs, and
browsed desired forbs Camassia, Fritillaria). Large impact islands had widespread
evidence of goose nesting and loafing, with many goose nests (> 5) spread across the
island with extensive evidence of foraging (turned up soil) and loafing (deep piles of
geese feces). The ordinal cover class scores for all annual grasses present were summed
to determine invasive annual grass cover. Once summed, the values were normalized by
the island with the greatest number and cover of annual grass to create a normalized
index score of annual grass cover. Thus, values range from 0 (no annual grass) to 1 (the
most annual grass). Finally, because the sample size was too small to model the
interaction of grass and the deer-goose impact score, a synergistic impact score was
created to determine the relative effect of when both deer or goose impact and annual
grass were present. The synergistic impact score (Impact) was calculated by multiplying
the IAG index by the DG score. Again, this resulting value was normalized by the island
with the greatest synergistic impact value to get a normalized index of 0 (no IAG or deer
or geese) and 1 (the most IAG and largest deer and goose impact).

75

To model the impact of island area and invasive species on the five components
of community change (nativity, native evolutionary distinctiveness, evolutionary
importance, functional richness, decline rate), I used a multi-model inference approach
(Anderson & Burnham, 2004; Millington & Perry, 2011). For each component of
community change, I assessed the influence of Area, IAG, DG, and Impact alone, Area
with IAG, DG, and Impact, and IAG and DG together for eight candidate regression
models total. Regression models were run using Bayesian inference using the package
brms (Bürkner, 2017). Response and predictor variables were centered and standardized
before running each model. Each model was run with eight chains, each chain with
10,000 runs (5,000 warm-up), thinned to 10. Prior predictive sampling was used to
determine reasonable, non-flat priors. The intercept was given a prior of mean = 0,
standard deviation = 0.5, and parameters a prior probability of mean of – and standard
deviation of 1. All models were assessed for chain convergence and 𝑟̂ <1.03. To compare
model performance, the LOO information criterion (LOOIC) was used (Vehtari et al.,
2021), and model weights were assessed using the model-stacking approach (Yao et al.,
2018). Briefly, this approach weights models as more plausible that have the lowest
posterior predictive error. Model performance was calculated using the
compare_performance function in the performance R package (Lüdecke et al., 2021).
To determine the relative importance of each model predictor, the sum of model
weights of each model with the parameter was calculated, and parameters with greater
weight are more likely to be important. To display model predictions, values from the top
model were used to display the mean and 90% credible intervals of predictions. It is
important to note that credible intervals are not measures of estimation error around the
76

mean but the probability distribution of the outcome across each level in the respective
parameter (McElreath, 2020).
To determine if the changes in community composition between islands resulted
in directional change toward homogenization, I assessed changes in the nestedness
component of phylogenetic, trait, and taxonomic (based on the ordinal cover) ß-diversity
(Baselga, 2010, 2017) using the betapart R package (Baselga & Orme, 2012). For each
island, the distribution of pairwise nestedness was displayed for each time period, and if
the distribution of differences between island pairs was greater than zero, that was
evidence for homogenization, while differences less than zero were evidence of
divergence.
Finally, to assess if the drivers of community change could be detected in changes
in species-level island extirpations, hierarchical logistic mixed-models were used to
assess the influence of area, invasive species impact (IAG, DG, Impact), and nativity
(native or alien), and plant traits (persistence traits) with phylogenetic relatedness and
island as random effects. Like the community change regression models, the same
analytical process for multi-model selection was used to compare 31 candidate models
assessing various combinations of plant traits, area, and invasive species impact. All
analysis was performed in R version 4.0.4. (R Core Team, 2021).

RESULTS

Between the initial surveys and 2021, the degree and direction of community
change were mixed across the surveyed islands (Figure 2-4). The greatest change

77

occurred on the smallest rocky islands (Blind South, Swirl East, and West, Long Island
Rock 3) compared to the larger meadow-dominated islands. However, the magnitude of
change is likely due to the small island floras of the rocky islands (~ < 10 species).

Figure 2-4. NMDS ordination displaying change in plant communities based on species presences and
absences (A) and species cover (B) for thirteen islands in the southern San Juan archipelago. The size
of points denotes the degree of impact of invasive annual grasses, deer, and geese for each island and
visit. Lengths of arrows denote the degree of change in plant composition. (BlindS island did not have
cover taken on initial surveys, so it is not in panel B).

QUESTION ONE: DO FOUR COMPONENTS OF PLANT COMMUNITY DIVERSITY
WITHIN AND ACROSS THE SAMPLED ISLANDS CHANGE BETWEEN THE INITIAL
SURVEYS AND 2021?

Overall, there is weakly-supported evidence (BF values ~ >1) for mean declines
in nativity and native biogeographically-weighted evolutionary distinctiveness across all
thirteen islands (Table 2-2). There was insufficient evidence suggesting functional
richness or evolutionary importance is declining. Still, given that moderately sized
78

declines are possible (within the 90% credible interval), it is likely to occur across some
combination of islands (Figure 2-5).
However, declines were more notable in the median values of each community
change component. Evolutionary importance had the greatest median decline (-35.6%)
from island floras capturing 28.5% of the regional evolutionary history to 18.3%. Native
BED had the second greatest median decline (-28.5%) from 30.0% of weighted
evolutionary history to 21.5%. The median decline in functional richness was a moderate
loss of 2 functional groups (-14.3% change) from 17.5 to 15 groups. Finally, nativity had
the smallest median decline (-5.8%) from 76.3% to 71.9%.
Table 2-2. Results of t-tests comparing four community change components between two time periods
fit with Bayesian inference. Log(BF) is the log of the Bayes Factor (roughly analogous to a t-statistic).
Difference is the mean and 90% highest density interval of the absolute difference between periods for
each component. % % difference is the mean percent difference between the two time periods in each
component value. *Nativity was rerun, excluding three outliers comprised of the smallest rocks that
are primarily shoreline flora and have few alien species present to begin with.
Component

log(BF)

Difference

% Difference

Nativity

1.07

-0.01(-0.05, 0.03)

-2.6

Nativity*

0.51

-0.04(-0.08, -0.004)

-6.85

Functional Richness

0.33

-0.77(-1.72, 0.18)

-6.25

Evolutionary Importance

0.4

-1.82(-4.08, 0.52)

8.46

Native BED

1.36

-5.35(-8.92, -1.57)

-19.44

79

Figure 2-5. Overall change in four components of community composition across 13 islands in the
southern San Juan archipelago. A) is the change in the biogeographically-weighted evolutionary
distinctiveness of native plants on each island, B) is the change in the total evolutionary importance of
the entire plant community of each island, C) Is the island-specific change in functional richness, D) is
the change in nativity (the proportion of native plants on each island). Red points and lines denote
changes through time in individual islands. Black points and lines denote the change in mean values of
each respective community composition component. Labeled islands denote outliers. Box plots denote
the minimum, maximum values (black horizontal lines), interquartile range (grey box), and median
(thick horizontal line) for each component and period). Violin plots denote the density and distribution
of values.

QUESTION TWO: DO MORE NATIVE SPECIES BECOME EXTIRPATED FROM
ISLANDS RATE THAN ALIEN SPECIES, AND ARE THEY BALANCED BY
COLONIZATION?

Native plants are much more likely to become extirpated compared to alien
plants. The overall median change in richness was 3.9 times greater for native plants than
80

alien plants. The median richness of native species declined 21.4% from 42 to 33 species
per island, compared to alien species, which only declined 5.6% from 18 to 17 species.
Across all islands, native plants became extirpated at a rate of 2.5 native plants to
every one alien plant lost on an island. Further, alien plants were more likely to colonize
an island than native plants at an overall rate of 1.6 alien plants for every one native plant
(Table 2-3).
Of the meadow islands, Goose Island, which completely burned in a wildfire in
June 2015, showed the greatest change in composition, which lost 54 species total, and
three native plants became extirpated for every one alien plant, while five alien plants
colonized for every one native plant (Table 2-3).
Table 2-3. The change in plant richness and the number of colonizations and extirpations for alien and
native plants across 14 islands in the southern San Juan Island archipelago. * islands primarily
comprised of shoreline habitat and vegetation.
Initial Survey

2021

Colonized

Extirpated

Island

Alien

Native

Alien

Native

Alien

Native

Total

Alien

Native

Total

Aleck Rock

20

66

21

60

3

2

5

2

8

10

Blind Island

17

58

18

54

2

1

3

5

5

Blind Island South*

1

4

Boulder Island

24

71

29

69

9

3

12

3

5

8

Castle Island

27

92

33

93

10

4

14

4

3

7

Flint Beach Island

21

64

23

60

4

3

7

2

7

9

Goose Island

21

55

17

16

10

2

12

13

41

54

Iceberg Island

25

51

25

48

2

5

7

2

8

10

Long Island Rock 1

19

32

20

33

4

4

8

3

3

6

Long Island Rock 2

16

34

17

33

2

2

4

1

1

2

Long Island Rock 3*

7

12

4

10

1

3

4

4

5

9

Swirl Rock Central*

5

18

5

13

2

2

2

5

7

2

2

1

1

4

Swirl Rock East*

4

3

Swirl Rock West*

5

4

1

1

1

1

Of the 21 rare species found across the study area, nine (42%) decreased in
frequency across the 14 sampled islands (Table 2-4). Three species became extirpated
across the islands; the disjunct shrub Shepherdia canadensis, the regionally rare perennial
81

grass Hordeum jubatum, and the perennial shoreline forb Sarcocornia pacifica. The
combined declines and extirpations were more frequent for disjunct plants (38%) than the
regionally rare plants (20%). The islands with the greatest community change also had
the largest decreases in rare species. Swirl Rock lost all its rare species, Goose Island lost
75% of the rare species flora, and Iceberg Island lost half of its rare species flora.
Table 2-4. change in the incidence of rare species across 14 islands along Southern Lopez Island
between two survey periods. * species listed as of special concern by the Washington Natural Heritage
Program.
Rarity Type

Taxon

2005-2009

2021

Aphyllon californicum ssp. californicum

8

5

Artemisia campestris var. scouleriana

3

3

Hornungia procumbens

5

3

Lepidium oxycarpum*

1

1

Lupinus microcarpus var. microcarpus

3

2

Myosurus minimus

2

2

Olsynium douglasii

1

1

Opuntia fragilis

7

5

2

1

6

5

Sabulina macra

4

3

Shepherdia canadensis

3

0

Triteleia grandiflora var. howellii

1

1

Arctostaphylos media

1

1

Carex pansa

1

1

Castilleja victoriae*

1

1

Epilobium glandulosum

1

1

Hordeum jubatum

1

0

Sarcocornia pacifica

1

0

Silene scouleri

2

2

Vaccinium ovatum

1

1

Disjunct

Oxytropis campestris var. spicata*
Ranunculus californicus*

1

Regionally Rare

1

Incidence records also include hybrids with Ranunculus occidentalis

82

HOW DO AREA, CANADA GEESE, DEER HERBIVORY, AND INVASIVE ANNUAL
GRASS INFLUENCE RATES OF COMMUNITY CHANGE?

The synergistic impact of invasive annual grasses (IAG) and deer and geese is the
strongest predictor of decline across all five community change components compared to
either factor individually (Table 2-5). Among the five community change components,
the greater the synergistic impact of geese, deer, and IAG, the larger the decline across all
four plant community components (Figure 2-6). The relative importance of synergistic
impact compared to area suggests that the synergistic influence of invasive species is a
more important predictor of species loss than what would be expected due to the expected
losses of species on smaller islands. Though, there is some evidence that area is a
potentially important predictor of changes in Native BED and the rate of native species
losses. There is also evidence that IAG cover alone is important in explaining the loss of
nativity.
Table 2-5 Model importance values for four model parameters explaining five community change
components. Importance values are the sum of model weights provided in Appendix B, Table B-1 for
each model with the parameter present within.
Factor

Evolutionary
Importance

Native
BED

Functional
Richness

Nativity

Decline
Rate

Area

0.080

0.242

0.010

<0.001

0.253

IAG

0.001

<0.001

<0.001

0.390

0.001

DG

<0.001

<0.001

<0.001

0.013

<0.001

Impact

0.918

0.758

0.900

0.610

0.746

Compared to the four islands with no synergistic impact (Castle, Long Island
Rock 1, Blind South, Swirl East, and West), Goose Island (the most impacted island;
furthest right point in each panel in Figure 2-6) had 1.02 times greater loss in
evolutionary importance, 94.6% greater loss in Native BED, 1.12 times greater reduction

83

in nativity, 92.5% greater loss in functional richness and a 96.6% higher decline rate in
native species.

Figure 2-6. Change in five components of community structure within 13 islands in the southern San
Juan archipelago. Points represent change values between initial surveys in 2005-2009 and 2021. A) Is
the island-specific change in functional richness, B) is the change in nativity (the proportion of native
plants on each island), C) is the change in the biogeographically-weighted evolutionary distinctiveness
of native plants on each island, D) is the change in the total evolutionary importance of the entire plant
community of each island, and E) is the rate of native species decline measured as the ratio of species
extirpations to colonizations. Lines represent 2000 draws of the posterior distribution of each model of
change. Areas of denser lines indicate more probable fits.

84

DO THE CHANGES IN SPECIES COMPOSITION LEAD TO BIOTIC
HOMOGENIZATION ACROSS THE SAMPLE ISLANDS?

There are no strong directional changes in the mean nestedness component of ßdiversity across phylogeny (mean = -0.48%, sd = 12.41%), traits (mean = -2.99%, sd =
39.37%) or plant cover (mean = -0.88%, sd = 31.24%). Island pairs were as likely to
become more related as they were to diverge (Figure 2-7).

Figure 2-7. The change in plant community nestedness between island pairs (points) among 13 islands
between initial surveys in 2005-2009 and 2021. Phylogeny represents the change in the pairwise
nestedness component of phylogenetic beta-diversity between island pairs based on their Jaccard
similarity. Cover and Traits represent the change in the pairwise balance component of abundance
weighted bray Curtis similarity between island pairs. Island pairs are considered homogenized if the
nestedness values increase with time.

85

HOW DOES ISLAND AREA, THE IMPACT OF INVASIVE SPECIES, PLANT TRAITS,
PLANT NATIVITY, AND PHYLOGENETIC RELATEDNESS INFLUENCE THE
PROBABILITY THAT A SPECIES WILL GO EXTINCT FROM AN ISLAND?
When predicting the individual probability that a species will become extirpated
on an island, species-specific traits are generally more important than either area or the
synergistic impact of invasive alien grasses, deer, and geese (Table 2-6, Figure 2-8).
Further, across all predictors, their interaction with species nativity is more important
than a given isolated predictor except for incidence, which could be equally informative
alone or interacting with nativity.
Table 2-6. Importance of five model parameters predicting species extirpation. Overall is the sum of
model weights in Appendix B Table B-2 for each model with the parameter present. Interaction
w/Nativity is the sum of model weights for each model where the parameter is interacting with
nativity. Additive is the sum of model weights for each model the parameter is present in isolation.
Factor

Overall

Interaction w/Nativity

Additive

Cover

0.700

0.477

0.223

Incidence

0.648

0.316

0.33

Persistence

0.626

0.382

0.244

Area

0.422

0.308

0.114

Impact

0.259

0.259

0

Species in the rare ordinal cover class are the most likely to become extirpated.
On average, rare native species are 12.9% more likely than rare alien species to become
extirpated, though there is significant variability (LCL diff = 19%, UCL diff = 5.5%;
Figure 2-6, panel A). Though, once species increase in cover, alien plants are slightly
more likely to become extirpated. Regionally rare species are also more likely to become
extirpated, and regardless of regional incidence, native plants are slightly more likely to
become extirpated than alien plants (Figure 2-6, panel B).
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Native species without persistence traits are 12.9% more likely to become
extirpated on average than alien non-persisters (LCL diff. = 19%, UCL diff. = 5.6%), and
16.4 more likely to become extirpated compared to native persisters (LCL diff. = 18%,
UCL diff. = 10%). There is no significant difference between persisters and nonpersisters among alien plants (mean diff. = 5.3) or native and alien persisters (mean diff.
= 1.7%; Figure 2-6, panel C).
Finally, island area does not significantly impact the probability that an alien plant
will become extirpated but has a small influence on native plants, which are more likely
to become extirpated on small islands than on larger ones (Figure 2-6, panel D).
There is weak evidence that impact is an informative predictor compared to island
area or life history alone. The potential importance of impact is only in interaction with
nativity. There was one model that had some support (weighted as the 4th most likely;
~Impact*Nativity+Inc, w =0.109; Appendix3, Table A3-2), and there is some evidence
that native species are more likely to become extirpated with increasing impact compared
to alien species (Appendix 3, Figure A3-1).

87

DISCUSSION

“We cannot discuss the ecology of islands without making a few disparaging comments
on goats.” – Koopowitz & Kaye, 1990

While Koopowitz and Kaye were referring to the dramatic effects of introduced
goats on oceanic islands in the quote above, the same sentiment is not difficult to have
towards introduced Canada geese and overabundant black-tailed deer. Despite the
extensive legal protections designed to conserve the islands and isolation from direct
human impacts, the small islands along the southern end of Lopez island have become
more degraded since the initial floristic inventories 12 to 16 years ago. During that time,
nesting Canada geese have increased in their number and extent across the islands. Such
increases have likely ratcheted the cumulative impacts of deer herbivory and other natural
island stressors on vascular plants such as nesting gulls and cormorants.
While there was some evidence of community-level declines across all four
diversity components (nativity, Native BED, evolutionary importance, and functional
richness), declines were generally small for nativity (average 5% loss in nativity) and
functional richness (average loss of 2.5 functional groups), the greatest loss was detected
in the evolutionary importance and distinctiveness (Native BED) of each island. While
the combined losses of native plants and additions of alien plants resulted in small to
modest reductions in evolutionary importance in 11 of the 14 islands (mean loss = 1.6%),
Goose Island lost 20% of its evolutionary importance. Within native species, the loss of
regionally rare species caused evolutionary distinctiveness to decrease across all but two
88

islands by 7.2 million years, with Goose Island losing the equivalence of 27.9 million
years of evolutionary history.
The patterns of community-level change were primarily driven by the
disproportionate loss of native plants relative to alien plants. While native and alien
plants became extirpated across all islands, nearly three times more native plants became
extirpated. Further, native species colonized islands less often than alien species. Due to
alien plants having an island-specific survival and colonization advantage, the sampled
islands are slowly losing their nativity. The loss of nativity and rate of native species
decline is likely due to the synergistic impact of Canada geese, deer herbivory, and
invasive annual grass. There was moderate to strong evidence that this synergistic impact
had a stronger effect than island size or geese, deer, or annual grass alone.
While there was strong to moderate evidence that individual islands are becoming
homogenized through the loss of native plants and gaining more alien plants, these
changes are not leading to directional community change towards biotic homogenization
across and between islands. The lack of inter-island homogenization is likely because the
identity of extirpated and colonizing plants is not consistent across islands, and 35% of
the flora did not change in frequency across the islands (Appendix 3, Table A3-3).
However, two invasive annual grasses (Bromus sterilis and Vulpia myuros) were the most
likely to colonize new islands, though invasive annual grasses were already present on
most islands during the initial surveys.
Currently, evidence suggests regionally rare species, which are also rare on
individual islands, and do not have a strong suite of persistence traits (woody, storage
organs such as bulbs, corms, deep taproots) are more likely to become extirpated, and this

89

likelihood of extirpation is greater for native plants compared to alien plants. Despite the
clear evidence of synergistic invasive species impact on community-level change,
modeling exercises did not show strong evidence for synergistic impacts as a driver of the
extirpation rates of individual taxa compared to knowing the regional incidence, cover,
and area of an island. However, there was evidence that synergistic impacts could be a
detectable component of species extirpations. At the greatest levels of synergistic impact,
native species are predicted to have a 10% greater chance of becoming extirpated
(68.7%) compared to alien species (58.3%), though the actual effect on species-level
extirpation was highly variable (LCL difference 9.8%, UCL difference = 3.5%; Appendix
3, Figure A3-1). So, while such effects of synergistic impacts are small to modest, the
impacts likely add up to meaningful differences when applied across the entire flora of an
island and group of islands.

THE CHALLENGE OF SCALE

Some of the difficulty in detecting species-level invasive species impacts is likely
due to the broadness of the data collected. While many species did not become extirpated
from islands with synergistic impacts, scale-dependent and obvious impacts could be
seen visually during visits and captured with photographs (Figure 2-8). A quadrat-based
sampling approach within an island comparing the most impacted areas with the least
would likely have the power to quantitatively detect change where simple presenceabsence could not. These difficult-to-quantify impacts include extensive soil turnover
from geese, which forage for rhizomes and roots. Geese can also add nutrients to thin
90

maritime meadow soils through their feces (Figure 2-9). Such additions likely benefit
annual competitive species such as grasses compared to native species (Best, 2008; Best
& Arcese, 2009). The effects of deer herbivory are well documented in the gulf islands,
where they can lead to the loss and significant decline in cover of their preferred forage.
In particular, the continued loss of flowering heads and associated seed production will
likely lead to a loss of non-clonal and short-lived species in time.

Figure 2-8. Two examples of difficult to capture impacts of deer and geese. In the left image,
vegetation has been extensively clipped, and flowers are short-stemmed from extensive deer browse.
In addition, the ground has been turned up from goose foraging for plant rhizomes and roots. In the
image on the right, geese have clipped and foraged most plant species except those they do not eat,
like Dodecatheon pulchellum (center of image). The image on the right was taken in May, and during
repeated visits in June, all the flowering heads had been eaten off by deer.

The extensive foraging of geese can also lead to “goose barrens,” where
vegetation is sparse, and the flora comprises native species the geese do not eat, such as
Sanicula crassicaulis, Toxicoscordion venenosum, and Camassia leichtlinii (Figure 2-9).
These barrens often occur in specific habitats where “rock gardens” are present; island

91

meadow microhabitats with rocky outcrops and small-scale soil deposits that are often
highly diverse on small scales, especially native annuals such as Plectritis, Collinsia, and
Trifolium. Such missing taxa are often still present on a given island in unreachable
microhabitats but are no longer significant components of overall flora. Further, such
unreachable microhabitats (such as cliff faces and inaccessible rock cracks) tend to have
lower protectivity and more risk from other environmental impacts such as winter storm
surges. For example, no geese were recorded on Aleck rock during the initial 2005-2009
surveys, but in 2021, at least 17 nests were found filled with 62 eggs total. As a result, we
found extensive damage to the coastal meadow community (Figure 2-9 second image).

Figure 2-9. Left image: an example of a ‘rock garden’ within a maritime meadow not yet impacted by
geese. Right image: a rock garden impacted by geese. Such “goose barrens” have been altered from
foraging and what remains are species geese do not eat (such as Camassia leichtlini).

92

THE PARABLE OF GOOSE ISLAND
Finally, two islands in particular – Goose Island and Swirl Rock – demonstrate
the concept of the extinction vortex (Gilpin, 1986), and what can happen when small
population size, invasive species, and unintentional human impact interact. Goose Island,
a small island just off the heavily visited Cattle Point area of San Juan Island, was
originally described as one of the highest quality examples of a maritime meadow
community (Eaton, 1980). However, nearly 40 years later, more than half the native flora
and 75% of the rare flora are now extirpated. While the island was already likely
impacted by nesting gulls and cormorants when it was first described, a wildfire burned
the entire island in mid-June 2015 due to some setting off a homemade firecracker from
nearby Cattle Point. During efforts to put the fire out, up to 100,000 gallons of salt water
were also put on the island in an unsuccessful attempt to put out the fire (“Goose Island
continues to burn,” 2015). While gulls and cormorants continue to nest on the island,
several Canada geese were noted in 2021 surveys, as was at least one pile of deer scat. In
addition, the island is now a densely grazed lawn of the annual grass Hordeum murinum,
which covers nearly 100% of the island's area suitable for growing vascular plants
(Figure 2-10).

93

Figure 2-10. Goose Island six years after a wildfire burned the entire island. Note the extensive cover
of annual grass and rocky outcrops devoid of plant life.

Swirl Rock is a small collection of three large, jagged rocks that are the most
isolated and furthest from larger islands such as Lopez or San Juan. The centermost rock
(Swirl Central) is the tallest, and the highest point of the island had several square meters
of soil capable of supporting several meadow taxa, including one of the three populations
of the WANHP sensitive species Oxytropis campestris var. spicata. Initial surveys of the
island noted no nesting Canada geese or invasive annual grasses. However, in 2021, there
was evidence of at least one Canada goose nest and extensive foraging sign. All the
meadow taxa, including O. campestris var. spicata found in the initial surveys, were
gone, and annual grass made a significant component of the flora (Figure 2-11).

94

Figure 2-11. the view from the top of Swirl Rock in 2021, the site of where a small patch of maritime
meadow once persisted, home to one of the three populations of the rare disjunct Oxytropis campestris
var. spicata. The area is heavily browsed and impacted by Canada geese (note extensive feces along
the top of the island), and the invasive annual grass Hordeum murinum (dried vegetation) dominates
the maritime meadow patch.

CONCLUSION
“Flowers as well as weeds follow in the footsteps of man” – Henry David Thoreau, A
Winter Walk
The patterns of native species decline and alien species colonization and
establishment described in this study continue to add to the growing body of evidence
that protected natural areas are not protecting biodiversity in light of species invasions
(Foxcroft et al., 2013, 2017; Hallmann et al., 2017; De la Fuente & Beck, 2018; Hulme,
2018; Ren et al., 2021). Moreover, invasive species are impacting protected and
imperiled ecological communities well beyond the frontier of human settlement and
development (Seabloom et al., 2006). In particular, this study supports the detailed
95

evidence demonstrating the negative consequences of introduced Canada geese (Best &
Arcese, 2009; Isaac-Renton et al., 2010; Bennett et al., 2011, 2013) as well as the
negative consequences of deer herbivory on the native flora of small meadow islands
(Martin, Arcese & Scheerder, 2011; Arcese et al., 2014, 2018). Without the rapid and
concerted effort to control both deer and Canada goose populations, the long-term
viability of these small island meadow communities is in significant doubt.
Studying biodiversity change on islands is a magnifying glass and amplifies the
potential patterns and processes happening at larger scales (Whittaker & FernándezPalacios, 2007). The islands on the southern edge of the San Juan archipelago were some
of the most unique and diverse found anywhere in the island chain. Yet, despite their
strong protection status and initially high nativity, the indirect impacts of species
introductions and human-caused accidents have led to the continued loss of biodiversity.
Such patterns highlight the reality that ‘do-nothing’ conservation is a management choice
that can still lead to ecological harm, especially in light of concepts of “compassionate
conservation” that pushes back against ideas of the lethal control of common invasive
species – especially birds and mammals (Hayward et al., 2019; Callen et al., 2020). The
small-island meadow communities urge us to revisit the idea of stewardship and the role
of humans in an ecosystem.
The idea of the Anthropocene suggests we are having strong, often unintentional
impacts on the natural world (Maslin & Lewis, 2015; Bonneuil & Fressoz, 2016), and
that the fate of the natural world is dependent upon which direction we choose (Crutzen
& Schwägerl, 2011; Sachs, 2011; Hamilton, 2015; Johnson et al., 2017). If we continue
to choose to do nothing, most of these small islands will likely continue to degrade and
96

shift towards annual grasslands with fewer species, a facsimile of the historic diversity,
the Homogecene will have come.

97

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131

APPENDIX 1 VASCULAR FLORA OF THE SAN JUAN
ARCHIPELAGO
Table A1-1. The vascular flora of the San Juan Island archipelago, Washington State, USA. ‘*’ alien
taxa, Habitat is the primary habitat a species is found on, and Islands are the number of islands the
species has been recorded on.
Family
Adoxaceae
Adoxaceae
Alismataceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaranthaceae
Amaryllidaceae
Amaryllidaceae
Amaryllidaceae
Amaryllidaceae
Amaryllidaceae
Amaryllidaceae
Amaryllidaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae

132

Full Species
Sambucus cerulea Raf.
Sambucus racemosa L.
Alisma triviale Pursh
Amaranthus blitoides S. Watson*
Amaranthus powellii S. Watson*
Atriplex dioica Raf.
Atriplex gmelinii C.A. Mey. ex
Bong.
Atriplex littoralis L.*
Atriplex patula L.*
Atriplex prostrata Boucher ex
DC.*
Chenopodiastrum murale (L.) S.
Fuentes, Uotila & Borsch*
Chenopodium berlandieri Moq.
Chenopodium leptophyllum
(Moq.) Nutt. ex S. Watson
Chenopodium macrosperma
Hook.f
Oxybasis rubra (L.) S. Fuentes,
Uotila & Borsch
Salicornia depressa Standl.
Salicornia pacifica Standl.
Sarcocornia pacifica Standl.
Allium acuminatum Hook.
Allium amplectens Torr.
Allium cernuum Roth
Allium sativum L.*
Allium vineale L.*
Narcissus poeticus L.*
Narcissus pseudonarcissus L.*
Angelica genuflexa Nutt.
Angelica lucida L.
Anthriscus caucalis M. Bieb.*
Carum carvi L.*
Cicuta douglasii (DC.) J.M. Coult.
& Rose
Conioselinum pacificum (S.
Watson) J.M. Coult. & Rose
Conium maculatum L.*
Daucus carota L.*
Daucus pusillus Michx.

Infra taxa
var. arborescens

var. gmelinii

var. zschackei
var.
leptophyllum

Habitat
Forest
Forest
Wetland
Open
Open
Shoreline
Shoreline

Islands
1
50
1
1
1
87
26

Shoreline
Shoreline
Shoreline

1
5
40

Open

1

Shoreline
Open

19
1

Wetland

1

Shoreline

2

Shoreline
Shoreline
Shoreline
Open
Open
Shoreline
Open
Open
Open
Forest
Wetland
Shoreline
Open
Open
Wetland

3
54
5
97
2
74
2
2
5
8
1
2
20
1
2

Wetland

30

Open
Open
Open

3
6
20

Family
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae

Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apiaceae
Apocynaceae
Apocynaceae
Apocynaceae
Aquifoliaceae
Araceae
Araceae
Araceae
Araceae
Araceae
Araceae
Araceae

Araceae
Araliaceae
Araliaceae
Aristolochiaceae
Asparagaceae
Asparagaceae
Asparagaceae

Full Species
Foeniculum vulgare Mill.*
Glehnia leiocarpa Mathias
Heracleum mantegazzianum
Sommier & Levier*
Heracleum maximum Bartr.
Lilaeopsis occidentalis J.M.
Coult. & Rose
Lomatium nudicaule (Pursh) J.M.
Coult. & Rose
Lomatium utriculatum (Nutt. ex
Torr. & A. Gray) J.M. Coult. &
Rose
Oenanthe sarmentosa C. Presl ex
DC.
Osmorhiza berteroi DC.
Osmorhiza purpurea (J.M. Coult.
& Rose) Suksd.
Perideridia montana (Blank.)
Dorn
Petrosedum erectum ('t Hart)
Grulich*
Petroselinum crispum (Mill.)
Fuss*
Pimpinella saxifraga L.*
Sanicula bipinnatifida Douglas ex
Hook.
Sanicula crassicaulis Poepp. ex
DC.
Sium suave Walter
Torilis arvensis (Huds.) Link*
Yabea microcarpa (Hook. & Arn.)
Koso-Pol.
Apocynum androsaemifolium L.
Vinca major L.*
Vinca minor L.*
Ilex aquifolium L.*
Arum italicum Mill.*
Lemna minor L.
Lemna trisulca L.
Lemna turionifera Landolt
Lysichiton americanus Hulten &
H. St. John
Spirodela polyrhiza (L.) Schleid.
Wolffia borealis (Engelm.)
Landolt & Wildi ex Gandhi,
Wiersema & Brouillet
Wolffia columbiana H. Karsten
Hedera helix L.*
Hedera hibernica (G. Kirchn.)
Bean*
Asarum caudatum Lindl.
Asparagus officinalis L.*
Brodiaea coronaria (Salisb.) Engl.
Brodiaea rosea (Greene) Baker

Infra taxa

Habitat
Open
Shoreline
Forest

Islands
3
1
3

Open
Shoreline

21
2

Open

43

Open

29

Wetland

12

Forest
Forest

29
4

Open

5

Shoreline

1

Open

2

ssp. nigra

Open
Open

1
12

var. crassicaulis

Open

78

ssp. arvensis

Wetland
Open
Wetland

1
7
1

Open
Forest
Forest
Open
Forest
Wetland
Wetland
Wetland
Wetland

2
5
1
24
3
2
3
8
5

Wetland
Wetland

3
2

Wetland
Forest
Forest

2
8
21

Forest
Open
Open
Open

2
5
62
5

var. rosea

133

Family
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Asparagaceae
Aspleniaceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae

134

Full Species
Camassia leichtlinii (Baker) S.
Watson
Camassia quamash (Pursh)
Greene
Dichelostemma congestum (Sm.)
Kunth
Hyacinthoides xmassartiana Heist.
ex Fabr.*
Maianthemum dilatatum (Alph.
Wood) A. Nelson & J.F. Macbr.
Maianthemum racemosum (L.)
Link
Maianthemum stellatum (L.) Link
Muscari armeniacum Leichtlin ex
Baker*
Ornithogalum umbellatum L.*
Scilla forbesii (Baker) Speta*
Triteleia grandiflora Lindl.
Triteleia hyacinthina (Lindl.)
Greene
Asplenium trichomanes L.
Achillea millefolium L.
Adenocaulon bicolor Hook.
Agoseris grandiflora (Nutt.)
Greene

Infra taxa
ssp. suksdorfii

Habitat
Open

Islands
95

ssp. maxima

Open

15

Open

1

Open

9

Forest

16

Forest

16

Forest
Open

7
2

Open
Open
Open
Open

1
1
10
23

Open
Open
Forest
Open

4
107
9
20

Agoseris heterophylla (Nutt.)
Greene
Ambrosia chamissonis (Less.)
Greene
Anaphalis margaritacea (L.)
Benth. & Hook. f.
Anisocarpus madioides Nutt.
Antennaria racemosa Hook.
Anthemis cotula L.*
Arctium minus (Hill) Bernh.*
Artemisia campestris L.
Artemisia suksdorfii Piper
Artemisia vulgaris L.*
Bellis perennis L.*
Bidens beckii Torr. ex Spreng.
Bidens frondosa L.
Calendula officinalis L.*
Carduus nutans L.*
Centaurea cyanus L.*
Centaurea diffusa Lam.*
Centaurea gerstlaueri Erdner*
Centaurea jacea L.*
Centaurea melitensis L.*
Centaurea montana L.*
Centaurea stoebe L.*
Centaurea varnensis Velen.*

var. heterophylla

Open

3

Shoreline

38

Open

12

Forest
Open
Open
Open
Open
Open
Open
Open
Wetland
Shoreline
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open

20
1
2
4
17
5
1
23
1
1
1
1
2
1
3
2
2
1
3
1

ssp.
amplexicaule

var. howellii

ssp. trichomanes

ssp. grandiflora,
ssp. leptophylla

var. scouleriana

ssp. australis

Family
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae

Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae

Full Species
Cichorium intybus L.*
Cirsium arvense (L.) Scop.*
Cirsium brevistylum Cronquist
Cirsium vulgare (Savi) Ten.*
Conyza canadensis (L.) Cronquist
Coreopsis grandiflora x C.
lanceolata *
Coreopsis lanceolata L.*
Cotula coronopifolia L.*
Crepis capillaris (L.) Wallr.*
Crepis nicaeensis Balbis ex Pers.*
Crocidium multicaule Hook.
Erigeron philadelphicus L.
Erigeron speciosus (Lindl.) DC.
Eriophyllum lanatum (Pursh) J.
Forbes
Filago arvensis L.*
Filago vulgaris Lam.*
Gamochaeta ustulata (Nutt.)
Holub
Gnaphalium palustre Nutt.
Gnaphalium uliginosum L.*
Grindelia integrifolia DC.
Hemizonella minima (A. Gray) A.
Gray
Hieracium albiflorum Hook.
Hieracium aurantiacum L.*
Hieracium caespitosum Dumort.*
Hieracium flagellare Willd.*
Hieracium stoloniflorum Waldst.
& Kit.*
Hypochaeris glabra L.*
Hypochaeris radicata L.*
Jacobaea maritima (L.) Pelser &
Meijden
Jacobaea maritima x J. vulgaris *
Jacobaea vulgaris Gaertn.*
Jaumea carnosa (Less.) A. Gray
Lactuca ludoviciana (Nutt.)
Riddell
Lactuca serriola L.*
Lapsana communis L.*
Leontodon autumnalis L.*
Leontodon saxatilis Lam.*
Leucanthemum maximum
(Ramond) DC.*
Leucanthemum vulgare Lam.*
Logfia minima (Sm.) Dumort.*
Madia exigua (Sm.) A. Gray
Madia glomerata Hook.
Madia gracilis (Sm.) D.D. Keck

Infra taxa

var. lanatum,
var.
leucophyllum

ssp. saxatilis

Habitat
Open
Open
Forest
Open
Open
Open

Islands
2
32
7
67
3
1

Open
Shoreline
Open
Open
Open
Forest
Open
Open

2
2
10
1
2
1
1
33

Open
Open
Open

1
4
26

Open
Open
Shoreline
Open

4
4
143
1

Forest
Open
Open
Open
Open

31
2
2
1
1

Open
Open
Open

24
88
1

Open
Open
Shoreline
Open

1
14
4
1

Open
Open
Open
Open
Open

9
13
4
4
1

Open
Open
Open
Open
Open

7
2
4
1
9

135

Family
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Asteraceae
Athyriaceae
Berberidaceae
Berberidaceae
Betulaceae
Betulaceae
Betulaceae
Betulaceae

136

Full Species
Madia sativa Molina
Matricaria discoidea DC.
Mauranthemum paludosum (Poir.)
Vogt & Oberpr.*
Microseris bigelovii (A. Gray)
Sch. Bip.
Mycelis muralis (L.) Dumort.*
Packera indecora (Greene) Á.
Löve & D. Löve
Packera macounii (Greene) W.A.
Weber & Á. Löve
Petasites frigidus (L.) Fr.
Pseudognaphalium stramineum
(Kunth) Anderb.
Pseudognaphalium thermale (E.E.
Nelson) G.L. Nesom
Psilocarphus tenellus Nutt.
Senecio sylvaticus L.*
Senecio vulgaris L.*
Sericocarpus rigidus Lindl.
Solidago elongata Nutt.
Solidago lepida DC.
Solidago simplex Kunth
Soliva sessilis Ruiz & Pav.*
Sonchus arvensis L.*
Sonchus asper (L.) Hill*
Sonchus oleraceus L.*
Symphyotrichum boreale (Torr. &
A. Gray) Á. Löve & D. Löve
Symphyotrichum subspicatum
(Nees) G.L. Nesom
Tanacetum balsamita L.*
Tanacetum parthenium (L.) Sch.
Bip.*
Tanacetum vulgare L.*
Taraxacum erythrospermum
Andrz. ex Besser*
Taraxacum officinale F.H. Wigg.*
Tragopogon dubius Scop.*
Tragopogon porrifolius L.*
Tragopogon pratensis L.*
Tripleurospermum inodorum (L.)
Sch. Bip.*
Athyrium filix-femina (L.) Roth
ex Mertens
Berberis aquifolium (Pursh) Nutt.
Berberis nervosa (Pursh) Nutt.
Alnus rubra Bong.
Alnus viridis (Chaix) DC.
Betula papyrifera Marshall
Betula pendula Roth*

Infra taxa

var. palmatus

var. salebrosa
var. nana, var.
simplex
ssp. arvensis
ssp. asper

ssp. cyclosorum

ssp. sinuata

Habitat
Open
Open
Open

Islands
5
6
1

Open

2

Forest
Open

28
1

Open

4

Wetland
Open

1
6

Open

6

Open
Open
Open
Open
Open
Open
Open

1
12
60
1
2
12
2

Open
Open
Open
Open
Wetland

12
16
71
102
1

Open

6

Open
Open

1
2

Open
Open

3
14

Open
Open
Open
Open
Open

68
4
4
1
4

Forest

19

Open
Forest
Forest
Forest
Forest
Forest

87
20
18
8
5
1

Family
Betulaceae
Blechnaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Boraginaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae

Full Species
Corylus cornuta Marshall
Struthiopteris spicant (L.) Weiss
Amsinckia intermedia Fisch. &
C.A. Mey.
Amsinckia menziesii (Lehm.) A.
Nelson & J.F. Macbr.
Amsinckia spectabilis Fisch. &
C.A. Mey.
Anchusa azurea Mill.*
Anchusa officinalis L.*
Borago officinalis L.*
Buglossoides arvensis (L.) I.M.
Johnst.*
Lycopsis arvensis L.*
Myosotis arvensis (L.) Hill*
Myosotis discolor Pers.*
Myosotis latifolia Poir.*
Myosotis laxa Lehm.
Myosotis stricta Link ex Roem. &
Schult.*
Myosotis sylvatica Ehrh. ex
Hoffm.*
Pentaglottis sempervirens (L.)
Tausch ex L.H. Bailey*
Plagiobothrys scouleri (Hook. &
Arn.) I.M. Johnst.
Plagiobothrys tenellus (Nutt. ex
Hook.) A. Gray
Symphytum officinale L.*
Symphytum uplandicum Nyman*
Alliaria petiolata (M. Bieb.)
Cavara & Grande*
Arabidopsis thaliana (L.) Heynh.*
Arabis caucasica Willd.*
Arabis eschscholtziana Andrz.
Aubrieta deltoidea (L.) DC.*
Barbarea orthoceras Ledeb.
Barbarea vulgaris W.T. Aiton*
Brassica juncea (L.) Czern.*
Brassica nigra (L.) W.D.J. Koch*
Brassica rapa L.*
Cakile edentula (Bigelow) Hook.*
Cakile maritima Scop.*
Camelina microcarpa Andrz. ex
DC.*
Capsella bursa-pastoris (L.)
Medik.*
Cardamine flexuosa With.*
Cardamine hirsuta L.*
Cardamine nuttallii Greene
Cardamine occidentalis (S.
Watson) Howell
Cardamine oligosperma Nutt.

Infra taxa
ssp. californica

var. spectabilis

var. edentula
ssp. maritima

Habitat
Forest
Forest
Open

Islands
3
5
3

Open

12

Open

5

Open
Open
Open
Open

2
1
1
1

Open
Open
Open
Open
Wetland
Open

1
4
43
1
4
12

Forest

1

Forest

1

Shoreline

28

Open

4

Open
Open
Forest

1
1
2

Open
Open
Open
Open
Open
Open
Open
Open
Open
Shoreline
Shoreline
Open

8
1
23
1
15
1
4
3
4
17
44
1

Open

10

Forest
Open
Forest
Wetland

6
66
2
2

Forest

50

137

Family
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Brassicaceae
Buddleja
Cabombaceae
Cactaceae
Campanulaceae
Campanulaceae
Campanulaceae
Campanulaceae
Campanulaceae
Campanulaceae
Campanulaceae
Campanulaceae
Caprifoliaceae
Caprifoliaceae

138

Full Species
Cardamine pensylvanica Muhl. ex
Willd.
Draba verna L.*
Erysimum cheiri (L.) Crantz*
Hesperis matronalis L.*
Hornungia procumbens (L.)
Hayek
Lepidium campestre (L.) W.T.
Aiton*
Lepidium densiflorum Schrad.
Lepidium didymum L.*
Lepidium draba L.*
Lepidium heterophyllum Benth.*
Lepidium latifolium L.*
Lepidium oxycarpum Torr. & A.
Gray
Lepidium perfoliatum L.*
Lepidium virginicum L.
Lobularia maritima (L.) Desv.*
Lunaria annua L.*
Nasturtium officinale W.T.
Aiton*
Raphanus raphanistrum L.*
Raphanus sativus L.*
Rorippa curvisiliqua (Hook.)
Bessey ex Britton
Rorippa palustris (L.) Besser
Sinapis arvensis L.*
Sisymbrium altissimum L.*
Sisymbrium officinale (L.) Scop.*
Teesdalia nudicaulis (L.) W.T.
Aiton*
Thlaspi arvense L.*
Turritis glabra L.
Buddleja davidii Franch.*
Brasenia schreberi J.F. Gmel.
Opuntia fragilis (Nutt.) Haw.
Campanula medium L.*
Campanula persicifolia L.*
Campanula rapunculoides L.*
Campanula rotundifolia L.
Campanula scouleri Hook. ex A.
DC.
Githopsis specularioides Nutt.
Lobelia dortmanna L.
Triodanis perfoliata (L.) Nieuwl.
Lonicera ciliosa (Pursh) Poir. ex
DC.
Lonicera hispidula (Lindl.)
Douglas ex Torr. & A. Gray

Infra taxa

ssp. menziesii

ssp. palustris

Habitat
Forest

Islands
4

Open
Open
Open
Shoreline

30
1
2
11

Open

1

Open
Open
Open
Open
Open
Shoreline

3
1
1
1
1
2

Open
Shoreline
Open
Forest
Wetland

1
72
2
3
2

Open
Open
Wetland

3
2
2

Wetland
Open
Open
Open
Open

1
3
1
3
5

Open
Open
Open
Wetland
Shoreline
Open
Open
Open
Open
Forest

1
49
1
2
27
2
1
1
14
4

Open
Wetland
Wetland
Forest

1
1
6
52

Forest

56

Family
Caprifoliaceae
Caprifoliaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae
Caryophyllaceae

Full Species
Lonicera involucrata (Richardson)
Banks ex Spreng.
Symphoricarpos albus (L.) S.F.
Blake
Agrostemma githago L.*
Arenaria serpyllifolia L.*
Cerastium arvense L.
Cerastium fontanum Baumg.*
Cerastium glomeratum Thuill.*
Cerastium pumilum Curtis*
Cerastium semidecandrum L.*
Cerastium tomentosum L.*
Dianthus armeria L.*
Dianthus barbatus L.*
Holosteum umbellatum L.*
Honckenya peploides (L.) Ehrh.
Lychnis coronaria (L.) Desr.*
Moehringia macrophylla (Hook.)
Fenzl
Moenchia erecta (L.) P. Gaertn.,
B. Mey. & Scherbius*
Sabulina macra (A. Nelson & J.F.
Macbr.) Dillenb. & Kadereit
Sagina apetala Ard.*
Sagina decumbens (Elliott) Torr.
& A. Gray
Sagina maxima A. Gray
Sagina procumbens L.*
Scleranthus annuus L.*
Silene antirrhina L.
Silene douglasii Hook.
Silene gallica L.*
Silene latifolia Poir.*
Silene menziesii Hook.
Silene scouleri Hook.
Spergula arvensis L.*
Spergularia canadensis (Pers.) G.
Don
Spergularia macrotheca
(Hornem.) Heynh.
Spergularia rubra (L.) J. Presl &
C. Presl*
Spergularia salina J. Presl & C.
Presl
Stellaria borealis Bigelow
Stellaria crispa Cham. & Schltdl.
Stellaria graminea L.*
Stellaria longifolia Muhl. ex
Willd.
Stellaria longipes Goldie
Stellaria media (L.) Vill.*
Stellaria nitens Nutt.

Infra taxa
var. involucrata

Habitat
Forest

Islands
9

var. laevigatus

Forest

94

Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Shoreline
Open
Forest

1
5
106
12
82
71
47
1
5
1
2
11
4
5

Open

2

Open

17

Shoreline
Shoreline

17
88

var. occidentalis

Shoreline
Shoreline
Open
Open
Open
Open
Open
Forest
Open
Shoreline
Shoreline

31
12
1
16
1
28
2
12
5
2
7

var. macrotheca

Shoreline

55

Shoreline

35

Shoreline

7

Wetland

6

Forest
Open
Wetland

10
1
2

Wetland
Open
Open

2
86
14

var. serpylilfolia
ssp. strictum
ssp. vulgare

ssp. armeria
ssp. barbatus
ssp. umbellatum
ssp. major

ssp. occidentalis
ssp. crassicaulis

ssp. scouleri

ssp. borealis, ssp.
sitchana

ssp. longipes

139

Family
Caryophyllaceae
Caryophyllaceae
Celastraceae
Ceratophyllaceae
Convolvulaceae
Convolvulaceae
Convolvulaceae
Convolvulaceae
Convolvulaceae
Convolvulaceae
Cornaceae
Cornaceae
Cornaceae
Crassulaceae
Crassulaceae
Crassulaceae
Crassulaceae
Crassulaceae
Crassulaceae
Crassulaceae
Crassulaceae
Cucurbitaceae
Cupressaceae
Cupressaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae

Full Species
Stellaria pallida (Dumort.)
Crépin*
Vaccaria hispanica (Mill.)
Rauschert*
Paxistima myrsinites (Pursh) Raf.
Ceratophyllum demersum L.
Calystegia lucana (Ten.) G. Don*
Calystegia sepium (L.) R. Br.
Calystegia soldanella (L.) R. Br.
Convolvulus arvensis L.*
Cuscuta epithymum Murray*
Cuscuta pacifica Costea &
M.A.R. Wright
Cornus occidentalis (Torr. & A.
Gray) Coville
Cornus stolonifera Michx.
Cornus unalaschkensis Ledeb.
Crassula connata (Ruiz & Pav.) A.
Berger
Crassula tillaea Lester-Garl.*
Sedum acre L.*
Sedum album L.*
Sedum divergens S. Watson
Sedum lanceolatum Torr.
Sedum oreganum Nutt.
Sedum spathulifolium Hook.
Marah oregana (Torr. & A. Gray)
Howell
Juniperus scopulorum Sarg.
Thuja plicata Donn ex D. Don
Bolboschoenus maritimus (L.)
Palla
Carex aquatilis Wahlenb.

Cyperaceae

Carex arcta Boott
Carex aurea Nutt.
Carex canescens L.
Carex canescens L.*
Carex cusickii Mack. ex Piper &
Beattie
Carex densa (L.H. Bailey) L.H.
Bailey
Carex echinata Murray

Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae

Carex exsiccata L.H. Bailey
Carex hendersonii L.H. Bailey
Carex hoodii Boott
Carex inops L.H. Bailey
Carex interior L.H. Bailey

Cyperaceae

140

Infra taxa

var. epithymum
var. pacifica

ssp. paludosus
var. aquatilis,
var. dives

ssp. echinata,
ssp.
phyllomanica

ssp. Inops

Habitat
Open

Islands
21

Open

1

Forest
Wetland
Open
Shoreline
Shoreline
Open
Shoreline
Shoreline

21
5
1
4
1
3
1
8

Forest

2

Forest
Forest
Shoreline

3
2
2

Shoreline
Shoreline
Shoreline
Open
Shoreline
Open
Shoreline
Open

9
3
9
1
93
2
79
5

Open
Forest
Wetland

61
24
8

Wetland

4

Wetland
Wetland
Wetland
Wetland
Wetland

3
3
2
2
4

Open

1

Wetland

2

Wetland
Wetland
Open
Open
Wetland

5
4
1
17
2

Family
Cyperaceae

Full Species
Carex kelloggii W. Boott

Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae

Carex laeviculmis Meinsh.
Carex lasiocarpa Ehrh.
Carex leporina L.
Carex leptalea Wahlenb.
Carex leptopoda Mack.
Carex leptopoda Mack.
Carex lyngbyei Hornem.
Carex macrocephala Willd. ex
Spreng.
Carex obnupta L.H. Bailey
Carex pachystachya Cham. ex
Steud.
Carex pansa L.H. Bailey
Carex pauciflora Lightf.
Carex pendula Huds.*
Carex praticola Rydb.
Carex rossii Boott
Carex stipata Muhl. ex Willd.
Carex subbracteata Mack.
Carex tumulicola Mack.
Carex unilateralis Mack.
Carex utriculata Boott
Carex vesicaria L.
Carex viridula Michx.
Carex vulpinoidea Michx.
Carex zikae E.H. Roalson & M.J.
Waterway
Dulichium arundinaceum (L.)
Britton
Eleocharis acicularis (L.) Roem.
& Schult.
Eleocharis macrostachya Britton
Eleocharis obtusa (Willd.) Schult.
Eleocharis palustris (L.) Roem. &
Schult.
Eleocharis parvula (Roem. &
Schultes) Link ex Bluff Nees, &
Schauer
Eriophorum chamissonis C.A.
Mey.
Eriophorum gracile W.D.J. Koch
ex Roth
Rhynchospora alba (L.) Vahl
Schoenoplectus acutus (Muhl. ex
Bigelow) Á. Löve & D. Löve
Schoenoplectus americanus
(Pers.) Volkart ex Schinz & R.
Keller
Schoenoplectus subterminalis
(Torr.) Soják

Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae

Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae

Cyperaceae

Infra taxa
var. impressa,
var. kelloggii,
var. limnophila

var. stipata

var. major
var. viridula

Habitat
Wetland

Islands
5

Wetland
Wetland
Wetland
Wetland
Forest
Forest
Shoreline
Shoreline

1
1
2
2
17
17
15
5

Wetland
Wetland

12
7

Open
Open
Forest
Open
Open
Wetland
Wetland
Open
Wetland
Wetland
Wetland
Shoreline
Open
Open

3
1
1
2
13
3
1
3
1
6
2
3
1
9

Wetland

4

Wetland

1

Wetland
Wetland
Wetland

4
1
7

Wetland

1

Wetland

1

Wetland

1

Wetland
Wetland

1
6

Shoreline

2

Wetland

1

141

Family
Cyperaceae
Cyperaceae
Cyperaceae
Cyperaceae
Cystopteridaceae
Dennstaedtiaceae
Dipsacaceae
Droseraceae
Dryopteridaceae
Dryopteridaceae
Dryopteridaceae
Elaeagnaceae
Elaeagnaceae
Equisetaceae
Equisetaceae
Equisetaceae
Equisetaceae
Equisetaceae
Equisetaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae

142

Full Species
Schoenoplectus tabernaemontani
(C.C. Gmel.) Palla
Scirpus atrocinctus Fernald
Scirpus cyperinus (L.) Kunth*
Scirpus microcarpus J. Presl & C.
Presl
Cystopteris fragilis (L.) Bernh.
Pteridium aquilinum (L.) Kuhn
Dipsacus fullonum L.*
Drosera rotundifolia L.
Dryopteris arguta (Kaulf.) Maxon
Dryopteris expansa (C. Presl)
Fraser-Jenk. & Jermy
Polystichum munitum (Kaulf.) C.
Presl
Elaeagnus umbellata Thunb.*
Shepherdia canadensis (L.) Nutt.
Equisetum arvense L.
Equisetum ferrissii Clute
Equisetum fluviatile L.
Equisetum hyemale L.
Equisetum palustre L.
Equisetum telmateia Ehrh.
Allotropa virgata Torr. & A. Gray
Arbutus menziesii Pursh
Arctostaphylos columbiana Piper
Arctostaphylos media Greene
Arctostaphylos uva-ursi (L.)
Spreng.
Chimaphila menziesii (R. Br.)
Spreng.
Chimaphila umbellata (L.) W.P.C.
Barton
Gaultheria shallon Pursh
Kalmia microphylla (Hook.) A.
Heller
Moneses uniflora (L.) A. Gray
Monotropa hypopitys L.
Monotropa uniflora L.
Orthilia secunda (L.) House
Pterospora andromedea Nutt.
Pyrola aphylla Sm.
Pyrola asarifolia Michx.
Pyrola chlorantha Sw.
Pyrola dentata Sm.
Pyrola minor L.
Pyrola picta Sm.
Rhododendron columbianum
(Piper) Harmaja

Infra taxa

Habitat
Wetland

Islands
3

Wetland
Wetland
Wetland

1
1
5

Forest
Forest
Open
Wetland
Forest
Forest

7
30
5
3
1
14

Forest

50

Open
Forest
Open
Open
Wetland
Wetland
Wetland
Wetland
Forest
Forest
Open
Open
Open

1
21
13
1
3
9
5
13
2
62
2
1
7

Forest

3

ssp. umellata

Forest

4

var. occidentalis

Forest
Wetland

37
3

Forest
Forest
Forest
Forest
Forest
Forest
Forest

1
2
13
2
2
1
4

Forest
Forest
Forest
Forest
Forest

2
1
1
3
1

var. pubescens

ssp. affine
ssp. braunii

ssp. asarifolia,
ssp. bracteata

Family
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Ericaceae
Euphorbiaceae
Euphorbiaceae
Euphorbiaceae
Euphorbiaceae
Euphorbiaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae

Full Species
Rhododendron groenlandicum
(Oeder) Kron & Judd
Rhododendron macrophyllum D.
Don ex G. Don
Vaccinium cespitosum Michx.
Vaccinium ovatum Pursh
Vaccinium oxycoccos L.
Vaccinium parvifolium Sm.
Vaccinium uliginosum L.
Euphorbia characias L.*
Euphorbia cyparissias L.*
Euphorbia elongata Poir.*
Euphorbia myrsinites L.*
Euphorbia peplus L.*
Acmispon americanus (Nutt.)
Rydb.
Acmispon denticulatus (Drew)
Sokoloff
Acmispon parviflorus (Benth.)
D.D. Sokoloff
Cytisus scoparius (L.) Link*
Laburnum anagyroidis Medik.*
Lathyrus aphaca L.*
Lathyrus japonicus Willd.
Lathyrus latifolius L.*
Lathyrus littoralis (Nutt.) Endl. ex
Walp.
Lathyrus nevadensis S. Watson
Lathyrus palustris L.
Lathyrus sylvestris L.*
Lotus corniculatus L.*
Lotus tenuis Waldst. & Kit. ex
Willd.*
Lupinus arboreus Sims*
Lupinus bicolor Lindl.
Lupinus latifolius Lindl. ex J.
Agardh
Lupinus littoralis Douglas
Lupinus microcarpus Sims
Lupinus pachylobus Greene
Lupinus rivularis Douglas ex
Lindl.
Medicago arabica (L.) Huds.*
Medicago lupulina L.*
Medicago sativa L.*
Melilotus albus Medik.*
Melilotus officinalis (L.) Lam.*
Oxytropis campestris (L.) DC.
Pisum sativum L.*
Rupertia physodes (Douglas ex
Hook.) J.W. Grimes
Trifolium arvense L.*

Infra taxa

var. americanus

var. nevadensis

var. latifolius
var. littoralis
var. microcarpus

var. spicata

Habitat
Forest

Islands
5

Forest

1

Forest
Forest
Forest
Forest
Forest
Open
Open
Open
Open
Open
Open

1
4
2
21
1
1
4
1
1
3
4

Open

10

Open

17

Open
Forest
Open
Shoreline
Open
Shoreline

8
1
1
57
4
1

Forest
Shoreline
Open
Open
Open

47
5
1
8
2

Open
Open
Open

4
15
2

Open
Open
Open
Open

2
7
1
1

Open
Open
Open
Open
Open
Shoreline
Open
Open

1
7
2
2
2
3
1
2

Open

2

143

Family
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fabaceae
Fagaceae
Gentianaceae
Gentianaceae

Gentianaceae
Geraniaceae
Geraniaceae
Geraniaceae
Geraniaceae
Geraniaceae
Geraniaceae
Geraniaceae
Geraniaceae
Grossulariaceae
Grossulariaceae
Grossulariaceae

144

Full Species
Trifolium campestre Schreb.*
Trifolium depauperatum Desv.
Trifolium dichotomum Hook. &
Arn.
Trifolium dubium Sibth.*
Trifolium fragiferum L.*
Trifolium hybridum L.*
Trifolium incarnatum L.*
Trifolium microcephalum Pursh
Trifolium microdon Hook. & Arn.
Trifolium oliganthum Steud.
Trifolium pratense L.*
Trifolium repens L.*
Trifolium retusum L.*
Trifolium striatum L.*
Trifolium subterraneum L.*
Trifolium suffocatum L.*
Trifolium variegatum Nutt.
Trifolium willdenovii Spreng.
Trifolium wormskioldii Lehm.
Ulex europaeus L.*
Vicia americana Muhl. ex Willd.
Vicia cracca L.*
Vicia hirsuta (L.) Gray*
Vicia lathyroides L.*
Vicia nigricans Hook. & Arn.
Vicia sativa L.*
Vicia tetrasperma (L.) Schreb.*
Vicia villosa Roth*
Quercus garryana Douglas ex
Hook.
Centaurium erythraea Rafn*
Centaurium pulchellum (Sw.)
Hayek ex Hand.-Mazz., Stadlm.,
Janch. & Faltis*
Gentianella amarella (L.) Börner
Erodium cicutarium (L.) L\\\'Hér.
ex Aiton*
Geranium bicknellii Britton
Geranium carolinianum L.
Geranium dissectum L.*
Geranium lucidum L.*
Geranium molle L.*
Geranium pusillum L.*
Geranium robertianum L.*
Ribes divaricatum Douglas
Ribes lacustre (Pers.) Poir.
Ribes sanguineum Pursh

Infra taxa

var. americana

var. gigantea
var. angustifolia,
var. sativa
var. glabrescens
var. garryana

ssp. acuta
ssp. cicutarium

var. divaricatum
var. sanguineum

Habitat
Open
Open
Open

Islands
8
1
8

Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Open
Forest
Open
Open
Open
Forest
Open

50
1
1
2
58
53
43
14
17
1
1
17
2
40
87
2
1
76
2
57
1
32
71

Open
Open
Open

1
4
38

Open
Open

5
1

Wetland
Open

3
26

Forest
Forest
Open
Open
Open
Open
Forest
Forest
Forest
Forest

1
5
23
2
99
2
6
63
10
54

Family
Haloragaceae
Haloragaceae
Hydrangeaceae
Hydrocharitaceae
Hydrocharitaceae
Hydrocharitaceae
Hydrocharitaceae
Hydrophyllaceae
Hydrophyllaceae
Hydrophyllaceae
Hypericaceae
Hypericaceae
Hypericaceae
Hypericaceae
Iridaceae
Iridaceae
Iridaceae
Iridaceae
Iridaceae
Iridaceae
Iridaceae

Full Species
Myriophyllum sibiricum Kom.
Myriophyllum verticillatum L.
Philadelphus lewisii Pursh
Egeria densa Planch.*
Elodea canadensis Michx.
Najas canadensis Michx.
Najas flexilis (Willd.) Rostk. &
W.L.E. Schmidt
Nemophila parviflora Douglas ex
Benth.
Nemophila pedunculata Douglas
ex Benth.
Phacelia linearis (Pursh) Holz.
Hypericum anagalloides Cham. &
Schltdl.
Hypericum calycinum L.*
Hypericum perforatum L.*
Hypericum scouleri Hook.
Crocus stellaris Haw.*
Iris foetidissima L.*
Iris germanica L.*
Iris pseudacorus L.*
Olsynium douglasii (A. Dietr.)
E.P. Bicknell
Sisyrinchium californicum (Ker
Gawl.) W.T.Aiton
Sisyrinchium idahoense E.P.
Bicknell

Isoetaceae
Isoetaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae

Isoetes nuttallii A. Br.
Isoetes occidentalis L.F. Hend.
Juncus acuminatus Michx.
Juncus alpinoarticulatus Chaix
Juncus articulatus L.
Juncus balticus Willd.
Juncus bolanderi Engelm.
Juncus breweri Engelm.
Juncus bufonius L.
Juncus effusus L.

Juncaceae
Juncaceae
Juncaceae
Juncaceae

Juncus ensifolius Wikstr.
Juncus gerardi Loisel.
Juncus hesperius (Piper) Lint
Juncus occidentalis (Coville)
Wiegand
Juncus tenuis Willd.
Luzula comosa E. Mey.
Luzula macrantha (S. Watson)
Zika & B.L. Wilson
Luzula multiflora (Ehrh.) Lej.
Luzula parviflora (Ehrh.) Desv.
Luzula subsessilis (S. Watson)
Buchenau

Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae
Juncaceae

Infra taxa

Habitat
Wetland
Wetland
Forest
Wetland
Wetland
Wetland
Wetland

Islands
4
3
7
1
3
1
3

var. parviflora,
var. austiniae

Forest

14

Forest

1

Open
Wetland

1
3

Open
Open
Wetland
Open
Open
Open
Wetland
Open

1
7
2
1
2
7
6
6

Open

1

Open

8

Wetland
Wetland
Wetland
Wetland
Wetland
Shoreline
Shoreline
Shoreline
Shoreline
Shoreline

1
1
4
1
4
19
1
2
23
13

Wetland
Shoreline
Wetland
Wetland

7
3
8
2

Wetland
Open
Open

3
24
10

Open
Forest
Open

2
2
58

var. douglasii

var. macounii,
var. segetum

ssp. articulata
ssp. ater

var. bufonius
ssp. pacificus,
ssp. effusus
ssp. gerardi

var. laxa

145

Family
Juncaginaceae
Juncaginaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lamiaceae
Lentibulariaceae
Lentibulariaceae
Lentibulariaceae
Liliaceae
Liliaceae
Liliaceae
Liliaceae
Liliaceae
Linnaeaceae
Lycopodiaceae
Lythraceae
Malvaceae
Malvaceae
Malvaceae
Malvaceae
Melanthiaceae
Menyanthaceae

146

Full Species
Triglochin concinna J.B. Davy
Triglochin maritima L.
Ajuga reptans L.*
Clinopodium douglasii (Benth.)
Kuntze
Glechoma hederacea L.*
Lamiastrum galeobdolon (L.)
Ehrend. & Polatschek*
Lamium amplexicaule L.*
Lamium hybridum Vill.*
Lamium purpureum L.*
Lycopus americanus Muhl. ex
W.P.C. Bartr.
Lycopus europaeus L.*
Lycopus uniflorus Michx.
Marrubium vulgare L.*
Melissa officinalis L.*
Mentha canadensis L.
Mentha piperita L.*
Mentha pulegium L.*
Mentha rotundifolia (L.) Huds.*
Nepeta cataria L.*
Prunella vulgaris L.
Satureja douglasii (Benth.)
Kuntze
Scutellaria galericulata L.
Stachys cooleyae A. Heller
Stachys mexicana Benth.
Thymus pulegioides L.*
Utricularia gibba L.
Utricularia minor L.
Utricularia vulgaris L.
Erythronium oregonum Applegate
Fritillaria affinis (Schult. &
Schult. f.) Sealy
Lilium columbianum Leichtlin
Prosartes hookeri Torr.
Tulipa sp. L.*
Linnaea borealis L.
Lycopodium clavatum L.
Lythrum salicaria L.*
Alcea rosea L.*
Malva neglecta Wallr.*
Malva sylvestris L.*
Sidalcea hendersonii S. Watson
Toxicoscordion venenosum (S.
Watson) Rydb.
Menyanthes trifoliata L.

Infra taxa

ssp. argentatum

var. lanceolata,
var. vulgaris

ssp. macrohiza
ssp. oregonum

ssp. longiflora

var. venenosum

Habitat
Wetland
Wetland
Forest
Forest

Islands
1
10
4
34

Forest
Forest

2
3

Open
Open
Open
Wetland

5
1
14
1

Wetland
Wetland
Open
Open
Wetland
Open
Open
Open
Open
Open

2
5
7
1
5
1
1
1
2
11

Forest

36

Wetland
Forest
Forest
Open
Wetland
Wetland
Wetland
Forest
Open

2
5
1
1
1
1
4
32
86

Forest
Forest
Open
Forest
Wetland
Wetland
Open
Open
Open
Shoreline
Open

19
1
1
9
2
4
1
1
1
2
61

Wetland

2

Family
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Montiaceae
Nyctaginaceae
Nymphaeaceae
Nymphaeaceae
Okay - possible
Oleaceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Onagraceae
Ophioglossaceae
Ophioglossaceae
Ophioglossaceae
Orchidaceae
Orchidaceae

Full Species
Calandrinia ciliata (Ruiz & Pav.)
DC.
Claytonia exigua Douglas ex Torr.
& A. Gray
Claytonia parviflora Douglas ex
Hook.
Claytonia perfoliata Donn ex
Willd.
Claytonia rubra (Howell) Tidestr.
Claytonia sibirica L.
Montia dichotoma (Nutt.) Howell
Montia fontana L.
Montia howellii S. Watson
Montia linearis (Douglas) Greene
Montia parvifolia (Moc. ex DC.)
Greene
Abronia latifolia Eschsch.
Nuphar polysepala Engelm.
Nymphaea odorata Aiton*
Solanum americanum Mill.
Ligustrum vulgare L.*
Camissonia contorta (Douglas)
Kearney
Chamaenerion angustifolium (L.)
Scop.
Circaea alpina L.
Clarkia amoena (Lehm.) A.
Nelson & J.F. Macbr.
Clarkia gracilis (Piper) A. Nelson
& J.F. Macbr.
Epilobium anagallidifolium Lam.
Epilobium brachycarpum C. Presl
Epilobium ciliatum Raf.
Epilobium densiflorum (Lindl.)
Hoch & P.H. Raven
Epilobium glandulosum Lehm.
Epilobium hirsutum L.*
Epilobium lactiflorum Hausskn.
Epilobium leptophyllum Raf.
Epilobium minutum Lindl.
Epilobium palustre L.
Epilobium torreyi (S. Watson)
Hoch & P.H. Raven
Ludwigia palustris (L.) Elliott
Oenothera glazioviana Micheli*
Botrypus virginianus (L.) Michx.
Ophioglossum pusillum Raf.
Sceptridium multifidum (Gmel.)
Tagawa
Calypso bulbosa (L.) Oakes
Cephalanthera austiniae (A. Gray)
A. Heller

Infra taxa

Habitat
Shoreline

Islands
27

ssp. exigua, ssp.
glauca

Shoreline

30

Open

21

Forest

91

Shoreline
Forest
Open
Shoreline
Shoreline
Open
Open

75
7
2
16
2
6
21

Shoreline
Wetland
Wetland
Open
Forest
Open

3
6
2
1
1
1

Open

26

ssp. pacifica

Forest
Open

6
11

ssp. gracilis

Open

2

Forest
Open
Open
Wetland

1
14
27
2

Open
Open
Open
Wetland
Open
Wetland
Wetland

2
2
1
2
28
1
1

Wetland
Open
Forest
Forest
Forest

3
1
1
1
6

Forest
Forest

19
3

var. occidentalis

147

Family
Orchidaceae

Full Species
Corallorhiza maculata (Raf.) Raf.

Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae

Corallorhiza mertensiana Bong.
Corallorhiza striata Lindl.
Epipactis helleborine (L.) Crantz*
Goodyera oblongifolia Raf.
Neottia banksiana (Lind.) Rchb. f.
Neottia convallarioides (Sw.)
Richardson
Neottia cordata (L.) Richardson*
Platanthera dilatata (Pursh) Lindl.
ex L.C. Beck

Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orchidaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Orobanchaceae
Oxalidaceae
Papaveraceae
Papaveraceae
Papaveraceae
Papaveraceae
Papaveraceae
Papaveraceae
Papaveraceae

148

Platanthera elegans Lindl.
Platanthera elongata (Rydb.) R.M.
Bateman
Platanthera orbiculata (Pursh)
Lindl.
Platanthera stricta Lindl.
Platanthera transversa (Suksd.)
R.M. Bateman
Platanthera unalascensis (Spreng.)
Kurtz
Spiranthes romanzoffiana Cham.
Aphyllon californicum (Cham. &
Schltdl.) A. Gray
Aphyllon purpureum (A. Heller)
Holub
Bellardia viscosa (L.) Fisch. &
C.A. Mey.*
Castilleja attenuata (A. Gray) T.I.
Chuang & Heckard
Castilleja hispida Benth.
Castilleja levisecta Greenm.
Castilleja victoriae Fairbarns &
J.M. Egger
Euphrasia nemorosa (Pers.)
Wallr.*
Kopsiopsis hookeri (Walp.)
Govaerts
Orthocarpus bracteosus Benth.
Rhinanthus minor L.
Triphysaria pusilla (Benth.) T.I.
Chuang & Heckard
Oxalis corniculata L.*
Corydalis lutea (L.) DC.*
Dicentra formosa (Haw.) Walp.
Eschscholzia californica Cham.*
Fumaria officinalis L.*
Meconella oregana Nutt.
Papaver rhoeas L.*
Papaver somniferum L.*

Infra taxa
var. maculata,
var. occidentalis
var. striata

var. albiflora,
var. leucostachys
ssp. elegans

ssp. californicum

var. hispida

ssp. formosa
ssp. californica

Habitat
Forest

Islands
21

Forest
Forest
Forest
Forest
Forest
Forest

3
4
12
29
2
1

Forest
Forest

7
3

Open
Forest

43
4

Forest

2

Forest
Forest

1
6

Forest

10

Open
Open

8
33

Open

29

Open

3

Open

10

Open
Open
Open

47
2
1

Open

3

Forest

2

Open
Open
Open

1
1
35

Open
Forest
Forest
Open
Open
Open
Open
Open

1
1
2
9
1
2
1
2

Family
Phrymaceae

Phrymaceae
Phrymaceae
Phrymaceae
Phrymaceae
Phrymaceae
Pinaceae
Pinaceae
Pinaceae
Pinaceae

Full Species
Erythranthe alsinoides (Douglas
ex Benth.) G.L. Nesom & N.S.
Fraga
Erythranthe guttata (Fisch. ex
DC.) G.L. Nesom
Erythranthe microphylla (Benth.)
G.L. Nesom
Erythranthe moschata (Douglas ex
Lindl.) G.L. Nesom
Erythranthe nasuta (Greene) G.L.
Nesom
Erythranthe ptilota G.L. Nesom
Abies grandis (Douglas ex D.
Don) Lindl.
Picea sitchensis (Bong.) Carrière
Pinus contorta Douglas ex
Loudon

Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae

Pinus monticola Douglas ex D.
Don
Pseudotsuga menziesii (Mirb.)
Franco
Tsuga heterophylla (Raf.) Sarg.
Antirrhinum majus L.*
Callitriche heterophylla Pursh
Callitriche palustris L.
Collinsia grandiflora Lindl.
Collinsia parviflora Lindl.
Cymbalaria muralis G. Gaertn., B.
Mey. & Scherb.*
Digitalis purpurea L.*
Hippuris vulgaris L.
Linaria dalmatica (L.) Mill.*
Linaria purpurea (L.) Mill.*
Linaria vulgaris Mill.*
Nuttallanthus texanus (Scheele)
D.A. Sutton
Plantago elongata Pursh
Plantago lanceolata L.*
Plantago major L.*
Plantago maritima L.
Veronica americana Schwein. ex
Benth.
Veronica arvensis L.*
Veronica chamaedrys L.*
Veronica filiformis Sm.*
Veronica officinalis L.*
Veronica peregrina L.
Veronica persica Poir.*
Veronica scutellata L.
Veronica serpyllifolia L.

Plumbaginaceae

Armeria maritima (Mill.) Willd.

Pinaceae
Pinaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae
Plantaginaceae

Infra taxa

var. contorta,
var. latifolia

var. menziesii

var. bolanderi

ssp. muralis
var. purpurea
ssp. dalmatica

var. xalapensis

var. humifusa,
var. serpyllifolia
ssp. californica

Habitat
Forest

Islands
26

Forest

21

Forest

6

Forest

2

Forest

23

Forest
Forest

1
34

Forest
Forest

18
27

Forest

2

Forest

75

Forest
Open
Wetland
Wetland
Open
Open
Open

16
2
2
2
25
84
2

Open
Wetland
Open
Open
Open
Open

12
5
2
1
1
1

Shoreline
Open
Open
Shoreline
Wetland

29
73
11
107
7

Open
Open
Open
Open
Wetland
Open
Wetland
Wetland

66
1
1
5
5
1
4
11

Shoreline

42

149

Family
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae

Full Species
Achnatherum lemmonii (Vasey)
Barkworth
Achnatherum nelsonii (Scribn.)
Barkworth
Agrostis capillaris L.*
Agrostis exarata Trin.
Agrostis gigantea Roth*
Agrostis microphylla Steud.
Agrostis pallens Trin.
Agrostis scabra Willd.
Agrostis stolonifera L.*
Aira caryophyllea L.*
Aira praecox L.*
Alopecurus aequalis Sobol.
Alopecurus geniculatus L.
Alopecurus pratensis L.*
Anthoxanthum odoratum L.*
Arrhenatherum elatius (L.) P.
Beauv. ex J. Presl & C. Presl*

Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae

Avena barbata Pott ex Link*
Avena fatua L.*
Avena sativa L.*
Bromus commutatus Schrad.*
Bromus diandrus Roth*
Bromus hordeaceus L.*
Bromus pacificus Shear
Bromus sitchensis Trin.

Poaceae
Poaceae
Poaceae
Poaceae

Bromus sterilis L.*
Bromus tectorum L.*
Bromus vulgaris (Hook.) Shear
Calamagrostis canadensis
(Michx.) P. Beauv.
Calamagrostis stricta (Timm)
Koeler
Cynosurus cristatus L.*
Cynosurus echinatus L.*
Dactylis glomerata L.*
Danthonia californica Bol.
Danthonia spicata (L.) P. Beauv.
ex Roem. & Schult.
Deschampsia caespitosa (L.) P.
Beauv.
Deschampsia danthonioides
(Trin.) Munro
Deschampsia elongata (Hook.)
Munro
Distichlis spicata (L.) Greene
Elymus elymoides (Raf.) Swezey

Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae

150

Infra taxa
ssp. lemmonii

Habitat
Open

Islands
6

ssp. dorei

Open

2

Open
Shoreline
Open
Wetland
Open
Open
Open
Open
Open
Wetland
Wetland
Open
Open
Open

9
28
6
1
6
4
18
106
123
4
4
5
25
4

Open
Open
Open
Open
Open
Open
Forest
Forest

4
2
1
4
106
124
30
104

Open
Open
Forest
Wetland

77
60
16
1

Wetland

1

Open
Open
Open
Open
Open

6
26
72
13
1

Wetland

4

Wetland

1

Wetland

3

Shoreline
Open

68
1

var. caryophyllea
var. aequalis

var. bulbosum,
var. elatius

var. carinatus,
var. marginatus,
var. sitchensis

ssp. inexpansa

ssp. brevifolius

Family
Poaceae
Poaceae
Poaceae

Poaceae
Poaceae

Full Species
Elymus glaucus Buckley
Elymus repens (L.) Gould*
Elymus trachycaulus (Link)
Gould ex Shinners
Festuca occidentalis Hook.
Festuca roemeri (Pavlick) E.B.
Alexeev
Festuca rubra L.
Festuca subulata Trin.
Festuca subuliflora Scribn.
Festuca trachyphylla (Hack.)
Krajina*
Glyceria borealis (Nash) Batch.
Glyceria elata (Nash) M.E. Jones
Glyceria occidentalis (Piper) J.C.
Nelson
Holcus lanatus L.*
Holcus mollis L.*
Hordeum brachyantherum Nevski
Hordeum depressum (Scribn. &
J.G. Sm.) Rydb.
Hordeum jubatum L.
Hordeum marinum Huds.*

Poaceae

Hordeum murinum L.*

Poaceae

Koeleria macrantha (Ledeb.)
Schult.
Leersia oryzoides (L.) Sw.
Leymus mollis (Trin.) Pilg.
Leymus vancouverensis (Vasey)
Pilg.
Lolium multiflorum Lam.*
Lolium perenne L.*
Melica subulata (Griseb.) Scribn.
Panicum miliaceum L.*
Phalaris arundinacea L.*
Phleum pratense L.*
Poa annua L.*
Poa bulbosa L.*
Poa compressa L.*
Poa confinis Vasey
Poa howellii Vasey & Scribn.
Poa infirma Kunth*
Poa palustris L.*
Poa pratensis L.*
Poa secunda J. Presl
Poa trivialis L.*
Polypogon monspeliensis (L.)
Desf.*

Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae

Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae

Infra taxa
ssp. glaucus
ssp. trachycaulus

Habitat
Open
Open
Open

Islands
90
12
13

var. roemeri

Forest
Open

38
14

Open
Forest
Forest
Open

141
4
7
1

Wetland
Wetland
Wetland

3
2
1

Open
Open
Shoreline
Shoreline

78
1
43
6

Shoreline
Shoreline

4
1

Shoreline

66

Open

61

Wetland
Shoreline
Shoreline

1
66
1

Open
Open
Forest
Open
Open
Open
Open
Open
Open
Shoreline
Forest
Shoreline
Open
Open
Open
Open
Shoreline

3
19
38
1
10
6
98
26
43
12
2
1
3
80
5
5
10

ssp. mollis

ssp. Intermedium
ssp.
gussoneanum
ssp. glaucum,
ssp. leporinum,
ssp. murinum

ssp. mollis

ssp. millaceum

ssp. vivipara

ssp. secunda

151

Family
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Poaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polemoniaceae
Polygonaceae

Full Species
Puccinellia nutkaensis (J. Presl)
Fernald & Weath.
Puccinellia nuttalliana (Schult.)
Hitchc.
Puccinellia pumila (Vasey)
Hitchc.
Schedonorus arundinaceus
(Schreb.) Dumort.*
Schedonorus pratensis (Huds.) P.
Beauv.*
Secale cereale L.*
Setaria pumila (Poir.) Roem. &
Schult.*
Thinopyrum ponticum (Podp.)
Barkworth & D.R. Dewey*
Torreyochloa pallida (Torr.) G.L.
Church
Trisetum canescens Buckley
Trisetum cernuum Trin.
Vulpia bromoides (L.) Gray*
Vulpia microstachys (Nutt.)
Munro
Vulpia myuros (L.) C.C. Gmel.*
Collomia grandiflora Douglas ex
Lindl.
Collomia heterophylla Douglas ex
Hook.
Collomia linearis Nutt.
Gilia capitata Sims
Leptosiphon bicolor Nutt.
Leptosiphon minimus (H. Mason)
Battaglia
Microsteris gracilis (Hook.)
Greene
Navarretia intertexta (Benth.)
Hook.
Navarretia squarrosa (Eschsch.)
Hook. & Arn.
Polemonium pulcherrimum Hook.

Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae

Fallopia bohemica (Chrtek &
Chrtková) J.P. Bailey*
Fallopia convolvulus (L.) Á.
Löve*
Fallopia japonica (Houtt.) Ronse
Decr.*
Persicaria amphibia (L.) Gray
Persicaria hydropiper (L.) Spach*
Persicaria maculosa Gray*
Polygonum aviculare L.*

Polygonaceae
Polygonaceae
Polygonaceae

Polygonum douglasii Greene
Polygonum erectum L.
Polygonum fowleri B.L. Rob.

Polygonaceae
Polygonaceae

152

Infra taxa

Habitat
Shoreline

Islands
91

Shoreline

5

Shoreline

1

Open

30

Open

2

Open
Open

1
1

Open

1

var. pauciflora

Wetland

8

var. pauciflora

Forest
Forest
Open
Forest

17
10
107
10

Open
Open

88
1

Forest

5

Open
Open
Open
Open

1
1
3
6

Open

1

Open

3

Open

3

Open

2

Open

3

Open

2

Open

2

Wetland
Wetland
Open
Shoreline

5
1
2
56

Shoreline
Shoreline
Shoreline

4
1
6

var.
pulcherrimum

ssp. aviculare,
ssp.buxiforme,
ssp. depressum

ssp. fowleri

Family
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae
Polygonaceae

Polypodiaceae
Polypodiaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Potamogetonaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Primulaceae
Pteridaceae
Pteridaceae

Full Species
Polygonum minimum S. Watson
Polygonum nuttallii Small
Polygonum paronychia Cham. &
Schltdl.
Polygonum spergulariiforme
Meisn. ex Small
Rumex acetosella L.*
Rumex conglomeratus Murray*
Rumex crispus L.*
Rumex maritimus L.
Rumex obtusifolius L.*
Rumex occidentalis S. Watson
Rumex salicifolius Weinm.

Polypodium amorphum Suksd.
Polypodium glycyrrhiza D.C.
Eaton
Potamogeton amplifolius Tuck.
Potamogeton berchtoldii Fieber
Potamogeton crispus L.*
Potamogeton epihydrus Raf.
Potamogeton foliosus Raf.
Potamogeton friesii Rupr.
Potamogeton gramineus L.
Potamogeton illinoensis Morong
Potamogeton natans L.
Potamogeton obtusifolius Mertens
& W.D.J. Koch
Potamogeton praelongus Wulfen
Potamogeton pusillus L.
Potamogeton richardsonii (A.
Benn.) Rydb.
Potamogeton robbinsii Oakes
Potamogeton zosteriformis
Fernald
Stuckenia pectinata (L.) Borner
Cyclamen hederifolium Aiton*
Dodecatheon hendersonii A. Gray
Dodecatheon pulchellum (Raf.)
Merr.
Lysimachia arvensis (L.) U.
Manns & Anderb.*
Lysimachia europaea (L.) U.
Manns & Anderb.
Lysimachia latifolia (Hook.)
Cholewa
Lysimachia maritima (L.)
Galasso, Banfi & Soldano
Lysimachia nummularia L.*
Lysimachia thyrsiflora L.
Adiantum aleuticum (Rupr.) Paris
Aspidotis densa (Brack.) Lellinger

Infra taxa

ssp. fueginus
var. occidentalis
var. transitorius,
var.
triangulivalvis

var. pulchellum

var. aleuticum

Habitat
Open
Open
Shoreline

Islands
1
2
1

Shoreline

68

Open
Shoreline
Shoreline
Shoreline
Shoreline
Shoreline
Shoreline

78
6
28
3
5
11
22

Forest
Open

3
86

Wetland
Wetland
Wetland
Wetland
Wetland
Wetland
Wetland
Wetland
Wetland
Wetland

2
1
1
2
3
2
3
1
4
2

Wetland
Wetland
Wetland

4
1
2

Wetland
Wetland

2
4

Wetland
Forest
Open
Open

2
1
3
18

Open

6

Forest

4

Forest

36

Forest

2

Forest
Forest
Forest
Open

1
2
5
7

153

Family
Pteridaceae
Pteridaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Ranunculaceae
Rhamnaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae

154

Full Species
Cryptogramma acrostichoides R.
Br.
Pentagramma triangularis (Kaulf.)
Yatsk., Windham & E. Wollenw.
Anemone lyallii Britton
Aquilegia formosa Fisch. ex DC.
Aquilegia vulgaris L.*
Clematis vitalba L.*
Delphinium consolida L.*
Delphinium menziesii DC.
Ficaria verna Huds.*
Halerpestes cymbalaria (Pursh)
Greene
Helleborus foetidus L.*
Myosurus minimus L.
Ranunculus acris L.*
Ranunculus aquatilis L.
Ranunculus californicus Benth.
Ranunculus californicus x R.
occidentalis
Ranunculus flammula L.
Ranunculus macounii Britton
Ranunculus occidentalis Nutt.
Ranunculus repens L.*
Ranunculus sardous Crantz*
Ranunculus sceleratus L.
Ranunculus uncinatus D. Don
Frangula purshiana (DC.) A. Gray
ex J.G. Cooper
Amelanchier alnifolia (Nutt.)
Nutt. ex M. Roem.
Aphanes arvensis L.*
Aphanes australis Rydb.*
Aphanes occidentalis (Nutt.)
Rydb.
Comarum palustre L.
Cotoneaster dielsianus E. Pritz. ex
Diels*
Cotoneaster franchetii Bois*
Cotoneaster horizontalis Decne.*
Cotoneaster lacteus W.W. Sm.*
Cotoneaster rehderi Pojark.*
Cotoneaster simonsii Baker*
Crataegus douglasii Lindl.
Crataegus gaylussacia A. Heller
Crataegus monogyna Jacq.*
Drymocallis glandulosa (Lindl.)
Rydb.
Fragaria chiloensis (L.) Mill.
Fragaria vesca L.

Infra taxa

Habitat
Forest

Islands
4

Forest

17

Open
Open
Open
Open
Open
Open
Open
Shoreline

2
7
3
4
1
12
2
2

Forest
Open
Open
Wetland
Open
Open

2
28
4
2
10
8

Wetland

3

Wetland
Open
Open
Open
Wetland
Forest
Forest

2
52
8
1
2
12
3

Forest

77

Open
Open
Open

22
40
42

Wetland
Open

3
4

var. monogyna
ssp. glandulosa

Open
Open
Open
Open
Open
Forest
Forest
Open
Open

3
6
1
1
3
4
2
20
1

ssp. californica

Shoreline
Forest

6
31

var. formosa

var. diffusus

var. ovalis, var.
reptans
var. occidentalis

var. multifidus

Family
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae

Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae
Rosaceae

Full Species
Fragaria virginiana Mill.
Geum macrophyllum Willd.
Holodiscus discolor (Pursh)
Maxim.
Malus domestica (Suckow)
Borkh.*
Malus fusca (Raf.) C.K. Schneid.
Malus xdawsoniana Rehder.*
Oemleria cerasiformis (Torr. & A.
Gray ex Hook. & Arn.) J.W.
Landon
Physocarpus capitatus (Pursh)
Kuntze
Potentilla anserina L.
Potentilla argentea L.
Potentilla gracilis Douglas ex
Hook.
Potentilla recta L.*
Poterium sanguisorba L.*
Prunus avium (L.) L.*
Prunus cerasifera Ehrh.*
Prunus cerasus L.*
Prunus domestica L.*
Prunus emarginata (Douglas)
Eaton
Prunus laurocerasus L.*
Prunus lusitanica L.*
Prunus mahaleb L.*
Prunus pugetensis Jacobson &
Zika*
Prunus virginiana L.
Pyracantha coccinea M. Roem.*
Pyrus communis L.*
Pyrus nivalis Jacq.*
Rosa canina L.*
Rosa gymnocarpa Nutt.
Rosa nutkana C. Presl
Rosa pisocarpa A. Gray
Rosa rubiginosa L.*
Rosa rugosa Thunb.*
Rubus bifrons Vest*
Rubus laciniatus Willd.*
Rubus leucodermis Douglas ex
Torr. & A. Gray
Rubus nutkanus Moc. ex Ser.
Rubus spectabilis Pursh
Rubus ursinus Cham. & Schltdl.
Sorbaria kirilowii (Regel)
Maxim.*
Sorbus aucuparia L.*
Sorbus hybrida L.*

Infra taxa
ssp. glauca
var. discolor

ssp. anserina,
ssp. pacifica

var. polygamum

ssp. gymnocarpa
ssp. nutkana
var. pisocarpa

Habitat
Open
Forest
Forest

Islands
35
13
76

Open

17

Forest
Open
Forest

42
1
7

Forest

3

Wetland

24

Open
Open

1
1

Open
Open
Open
Open
Open
Open
Forest

2
1
10
7
3
6
39

Open
Open
Open
Open

2
1
6
1

Forest
Open
Open
Open
Open
Forest
Open
Forest
Open
Open
Open
Open
Forest

10
2
9
1
2
38
106
2
7
2
41
14
13

Forest
Forest
Open
Forest

19
20
82
1

Open
Open

9
1

155

Family
Rosaceae
Rosaceae
Rubiaceae
Rubiaceae
Rubiaceae

Saxifragaceae

Full Species
Sorbus intermedia (Ehrh.) Pers.*
Spiraea douglasii Hook.
Galium aparine L.
Galium boreale L.
Galium divaricatum Pourr. ex
Lam.*
Galium murale (L.) All.*
Galium odoratum (L.) Scop.*
Galium palustre L.
Galium trifidum L.
Galium triflorum Michx.
Sherardia arvensis L.*
Ruppia maritima L.
Populus alba L.*
Populus tremuloides Michx.
Populus trichocarpa Torr. & A.
Gray
Salix geyeriana Andersson
Salix hookeriana Barratt ex Hook.
Salix lasiandra Benth.
Salix prolixa Andersson
Salix scouleriana Barratt ex Hook.
Salix sitchensis Sanson ex Bong.
Arceuthobium tsugense (Rosend.)
G.N. Jones
Acer glabrum Torr.
Acer macrophyllum Pursh
Heuchera micrantha Douglas ex
Lindl.
Lithophragma glabrum Nutt.
Lithophragma parviflorum
(Hook.) Nutt.
Micranthes integrifolia (Hook.)
Small
Micranthes rufidula Small
Saxifraga austromontana Wiegand
Saxifraga cespitosa L.
Tellima grandiflora (Pursh)
Douglas ex Lindl.
Tiarella trifoliata L.

Scrophulariaceae
Scrophulariaceae
Selaginellaceae
Solanaceae
Solanaceae
Solanaceae
Taxaceae
Thymelaeaceae

Verbascum blattaria L.*
Verbascum thapsus L.*
Selaginella wallacei Hieron.
Solanum dulcamara L.*
Solanum physalifolium Rusby*
Solanum triflorum Nutt.*
Taxus brevifolia Nutt.
Daphne laureola L.*

Rubiaceae
Rubiaceae
Rubiaceae
Rubiaceae
Rubiaceae
Rubiaceae
Ruppiaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Salicaceae
Santalaceae
Sapindaceae
Sapindaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae
Saxifragaceae

156

Infra taxa

var. lasiandra

ssp. contortae
ssp. douglasii
var. diversifolia

var. laciniata,
var. trifoliata,
var. unifoliata

Habitat
Open
Wetland
Forest
Forest
Open

Islands
7
8
95
2
2

Open
Forest
Forest
Forest
Forest
Open
Shoreline
Open
Forest
Forest

2
3
2
5
18
8
3
2
8
7

Wetland
Wetland
Wetland
Wetland
Forest
Wetland
Forest

1
8
10
2
47
7
3

Forest
Forest
Forest

22
24
75

Open
Open

2
40

Open

19

Open
Open
Shoreline
Forest

1
4
42
18

Forest

11

Open
Open
Open
Open
Open
Open
Forest
Open

1
10
78
5
1
1
30
13

Family
Typhaceae
Typhaceae
Typhaceae
Typhaceae
Typhaceae
Ulmaceae
Urticaceae
Urticaceae
Valerianaceae
Valerianaceae
Valerianaceae
Valerianaceae
Valerianaceae
Violaceae
Violaceae
Violaceae
Violaceae
Violaceae
Violaceae
Violaceae
Violaceae
Vitaceae
Vitaceae
Woodsiaceae
Woodsiaceae

Full Species
Sparganium angustifolium Michx.
Sparganium emersum Rehmann
Sparganium eurycarpum Engelm.
Typha angustifolia L.*
Typha latifolia L.
Ulmus procera Salisb.*
Urtica dioica L.
Urtica urens L.*
Centranthus ruber (L.) DC.*
Plectritis brachystemon Fisch. &
C.A. Mey.
Plectritis congesta (Lindl.) DC.
Valeriana scouleri Rydb.
Valerianella locusta (L.) Laterr.*
Viola adunca Sm.
Viola glabella Nutt.
Viola howellii A. Gray
Viola langsdorffii Fisch. ex Ging.
Viola macloskeyi F.E. Lloyd
Viola odorata L.*
Viola palustris L.
Viola sempervirens Greene
Vitis labrusca L.*
Vitis vinifera L.*
Woodsia oregana D.C. Eaton
Woodsia scopulina D.C. Eaton

Infra taxa

ssp. gracilis

ssp. oregana
ssp. laurentiana,
ssp. scopulina

Habitat
Wetland
Wetland
Wetland
Wetland
Wetland
Forest
Forest
Open
Open
Open

Islands
4
2
1
3
9
3
38
1
1
3

Open
Forest
Open
Open
Forest
Forest
Wetland
Wetland
Forest
Wetland
Forest
Forest
Open
Forest
Forest

68
3
4
3
2
2
1
1
1
1
2
2
1
1
3

APPENDIX 2 – CHAPTER 1 TABLES
Table A2-1. Candidate models explaining the species area curve of islands and native and alien
species. Th1 and Th2 are the model-derived island size thresholds. Seg1-3 are the number of islands in
each threshold.
Habitat - Nativity

Model

AICc

BIC

R2

Th1

Th2

seg1

seg2

seg3

ContTwo

1339.5

1360.1

0.94

13.56

7114.22

139

14

3

ZslopeTwo

1345.6

1363.4

0.94

0.05

1028.32

46

104

6

ContOne

1385.5

1400.3

0.92

762.30

150

6

ZslopeOne

1473.0

1484.9

0.86

0.26

81

75

Linear

1559.0

1568.0

0.76

ContTwo

1142.2

1162.2

0.9

6984.37

13005.51

142

1

2

ZslopeTwo

1181.3

1198.5

0.86

0.08

4509.49

46

96

3

ContOne

1187.1

1201.6

0.86

1426.03

139

6

All Habitats - Native

All Species - Alien

157

Habitat - Nativity

Model

AICc

BIC

R2

Th1

ZslopeOne

1265.5

1277.2

0.75

3.27

Linear

1318.9

1327.6

0.63

ContTwo

897.1

917.7

0.8

1452.54

ContOne

908.5

923.3

0.78

1127.53

ZslopeTwo

909.6

927.4

0.78

0.002

ZslopeOne

955.8

967.7

0.7

0.01

Linear

959.2

968.2

0.69

Intercept

1139.6

1145.7

0

ContTwo

561.9

581.9

0.72

1637.3

ContOne

569.7

584.2

0.69

1459.24

ZslopeTwo

569.3

586.5

0.7

0.03

ZslopeOne

584.1

595.8

0.66

2.3

Linear

614.3

623.0

0.57

ZslopeTwo

1122

1139.7

0.88

0.03

ContTwo

1123.2

1143.8

0.88

0.03

ContOne

1137.1

1151.9

0.86

ZslopeOne

1189.0

1200.9

0.81

Linear

1221.0

1229.8

0.76

ContTwo

1105.2

1125.2

0.88

7313.53

ZslopeTwo

1143.3

1160.6

0.85

0.07

ContOne

1147.2

1161.7

0.84

ZslopeOne

1224.3

1235.9

0.73

Linear

1263.1

1271.9

0.64

ZslopeTwo

1071.3

1089

0.93

0.17

ContTwo

1070.1

1090.7

0.93

0.23

ZslopeOne

1095.0

1106.9

0.92

ContOne

1093.6

1108.4

0.92

Linear

1232.0

1241.0

0.79

ZslopeTwo

375.5

392.7

0.92

1.71

ContTwo

374.9

394.9

0.92

3.5

ContOne

438.2

452.6

0.88

1106.95

Th2

seg1

seg2

seg3

113

32

150

4

150

6

4

146

15

141

139

5

139

6

28

111

109

36

4700.32

35

118

3

4700.32

39

114

3

1486.37

150

6

0.07

54

102

11861.16

142

1

2

4406.84

42

100

3

1528.01

139

6

3.05

113

32

11806.67

75

79

2

11806.67

79

75

2

0.22

79

77

0.29

82

74

6083.13

106

36

3

6224.83

113

29

3

139

6

Shoreline - Native
14194.73

1153.79

2

6

Shoreline - Alien
14260.25

1637.3

1

6

Open - Native

Open - Alien

Forest - Native

Forest - Alien

158

Habitat - Nativity

Model

AICc

BIC

R2

Th1

ZslopeOne

485.1

496.7

0.83

820.59

Linear

648.2

657

0.47

ContTwo

695.7

716.3

0.98

52.74

ZslopeTwo

702.5

720.3

0.98

47.0

ContOne

874.3

889.1

0.94

ZslopeOne

885.8

897.7

0.93

Linear

1227.9

1236.8

0.36

ZslopeTwo

217.7

234.9

0.79

22.09

ContTwo

219.1

239.1

0.79

25.36

ZslopeOne

261.7

273.3

0.72

ContOne

260.7

275.2

0.72

Linear

382.1

390.9

0.34

Th2

seg1

seg2

seg3

139

6

13247.3

144

10

2

13247.3

144

10

2

400.1

150

6

356.56

150

6

7658.21

131

12

2

7658.21

131

12

2

46.15

133

12

187.99

137

8

Wetland - Native

Wetland - Alien

Figure A2-1. The residence time of alien plants in the Salish Sea region of the Pacific Northwest
based on their invasive plant status and life span. Each red dot represents an individual plant species,
the size of each dot increases with the observed occurrence frequency among surveyed islands.
Boxplots represent the 1st and 3rd quartiles (grey box), the minimum and maximum (black horizontal
line), and median (bold vertical line).

159

Figure A2-2. The residence time of alien plants in the Salish Sea region of the Pacific Northwest
based on their biogeographical category and life span. Each red dot represents an individual plant
species, the size of each dot increases with the observed occurrence frequency among surveyed
islands. Boxplots represent the 1st and 3rd quartiles (grey box), the minimum and maximum (black
horizontal line), and median (bold vertical line).

160

Figure A2-3. The residence time of alien plants in the Salish Sea region of the Pacific
Northwest based on whether the species is an horticultural escape and life span. Each red
dot represents an individual plant species, the size of each dot increases with the observed
occurrence frequency among surveyed islands. Boxplots represent the 1st and 3rd quartiles
(grey box), the minimum and maximum (black horizontal line), and median (bold vertical
line).

161

Figure A2-4. The residence time of alien plants in the Salish Sea region of the Pacific Northwest
based on the primary habitat a species grows in and life span. Each red dot represents an individual
plant species, the size of each dot increases with the observed occurrence frequency among surveyed
islands. Boxplots represent the 1st and 3rd quartiles (grey box), the minimum and maximum (black
horizontal line), and median (bold vertical line).

162

Figure A2-5. The residence time of alien plants in the Salish Sea region of the Pacific Northwest
based on the life form, dispersal type and life span. Each red dot represents an individual plant
species, the size of each dot increases with the observed occurrence frequency among surveyed
islands. Boxplots represent the 1st and 3rd quartiles (grey box), the minimum and maximum (black
horizontal line), and median (bold vertical line).

163

Table A2-2. The 20 candidate models describing the frequency of alien species across 145 islands in
the San Juan Island Archipelago. LOOIC is the leave-one-out cross-validation information criterion
and its standard error, the smaller the value the better relative fit. W is the model weight (the
probability the model is the optimal model) based on Bayesian stacking of the posterior-predictive
densities of each model. Thus, models with the greatest weights have the lowest relative predictive
error. R2 is the variance of each model’s predictions divided by the prediction variance and the
expected error variance, interpretation is roughly analogous to the classical R2 value.
Model*

LOOIC

w

R2Fixed

R2Full

TSFS+Ornamental+Status+Type

6438.3 (522.1)

0.46

0.38

0.57

Status+TSFS

7053.8 (573.3)

0.03

0.33

0.51

Ornamental+TSFS

7127.2 (576.7)

<0.01

0.30

0.53

Type+TSFS

7138.5 (583.6)

0.04

0.31

0.50

LifeSpan + TSFS

7186.0 (597.3)

0.07

0.31

0.50

TSFS+Clonal+Form+LifeSpan+Dispersal+Habitat

7212.6 (587.4)

0.06

0.32

0.50

TSFS+Dispersal+Form+LifeSpan

7216 (598.3)

0.01

0.31

0.51

Clonal+TSFS

7405.5 (599.0)

<0.01

0.29

0.45

Form+TSFS

7537.5 (612.1)

<0.01

0.27

0.49

TSFS

7537.5 (615.7)

0.02

0.27

0.46

Habitat+TSFS

7538.2 (607.2)

0.02

0.27

0.46

Dispersal+TSFS

7540.5 (617.6)

<0.01

0.27

0.46

Type

7873.0 (691.9)

0.07

0.24

0.36

Ornamental

7934.0 (658.4)

0.03

0.23

0.43

Status

7989.4 (703.6)

0.06

0.25

0.31

LifeSpan

8331.7 (737.0)

0.07

0.22

0.22

Clonal

8516.1 (725.4)

0.05

0.20

0.14

Dispersal

8660.7 (735.8)

<0.01

0.18

0.07

Form

8674.4 (739.6)

0.02

0.18

0.28

Habitat

8749.4 (738.5)

<0.01

0.18

0.05

*TSFS = residence time, Ornamental = introduced garden ornamental, Status = if invasive, transformer, or naturalized, Type = if
native, archaeophyte, or neophyte; Form = grass/forb/shrub/tree/vine; LifeSpan = annual/biennial/perennial; Dispersal =
Long/Short; Habitat = primary habitat (shoreline/open/forest/wetland).

164

APPENDIX 3 CHAPTER TWO TABLES
Table A3-1. Model comparison table of eight candidate models explaining five components of plant
diversity across 13 islands in the southern San Juan Island archipelago. Decline Rate is the ratio of the
number of native plant colonizations to native plant extirpations per island. Native EDbiogeo is the
change in the sum of evolutionary distinctiveness values for all native species on each island weighted
by each species regional incidence in the archipelago. Evolutionary Importance is the change in the
proportion of total evolutionary history represented on each island. Nativity is the change in the
proportion of each islands flora comprised of native plants. Functional Richness is the sum of the
number of unique combinations of dispersal type, lifespan, life form, and root form combinations.
LOOIC is the leave-one-out cross-validation information criterion and its standard error, the smaller
the value the better relative fit. W is the model weight (the probability the model is the optimal model)
based on Bayesian stacking of the posterior-predictive densities of each model. Thus, models with the
greatest weights have the lowest relative predictive error. R2 is the variance of each model’s
predictions divided by the prediction variance and the expected error variance, interpretation is
roughly analogous to the classical R2 value. Bolded models comprise  90% of model weights.
Component
Decline Rate

Model*

LOOIC

w

R2

Impact
Area
IAG
IAG + Area
Impact + Area
DG
DG + Area
IAG + DG

40.33(5.73)
42.72(7.13)
41.76(5.97)
43.2(5.73)
41.81(5.92)
44.63(8.01)
44.9(7.42)
44.98(6.79)

0.746
0.253
0.001
0.000
0.000
0.000
0.000
0.000

0.3
0.14
0.2
0.26
0.28
0.28
0.38
0.37

Impact
Area
DG
IAG
IAG + Area
DG + Area
Impact + Area
IAG + DG

41.02(8.75)
44.07(7.66)
42.79(7.27)
42.78(6.76)
43.75(6.01)
44.5(7.11)
41.92(7.1)
43.71(7.13)

0.758
0.242
0.000
0.000
0.000
0.000
0.000
0.000

0.38
0.08
0.32
0.16
0.21
0.39
0.26
0.4

Impact
Area
IAG
IAG + Area
Impact + Area
DG
DG + Area
DG + IAG

41.25(11.87)
48.9(15.28)
46.86(14.24)
47.08(12.22)
42.36(11.56)
46.25(13)
48.23(12.12)
46.79(11.17)

0.918
0.081
0.001
0.000
0.000
0.000
0.000
0.000

0.43
0.049
0.16
0.21
0.44
0.26
0.3
0.34

Impact
IAG
Impact + Area
IAG + Area
IAG + DG
Area
DG + Area
DG

-26.56(7.58)
-25.98(6.8)
-25.14(6.68)
-24.62(5.75)
-23.05(4.39)
-22.19(8.3)
-20.03(5.28)
-20.99(6)

0.610
0.390
0.000
0.000
0.000
0.000
0.000
0.000

0.42
0.35
0.44
0.37
0.48
0.14
0.42
0.35

 Native EDbiogeo

 Evo. Importance

 Nativity

 Functional Richness

165

Model*
LOOIC
w
R2
Impact
41.25(11.87)
0.900
0.43
Area
49.2(15.19)
0.100
0.038
IAG
48.3(13.72)
0.000
0.05
Impact+Area
46.97(11.69)
0.000
0.25
DG
48.51(12.39)
0.000
0.19
DG+IAG
50.54(12.03)
0.000
0.22
IAG+Area
49.42(13.34)
0.000
0.12
DG+Area
49.34(11.22)
0.000
0.23
*Impact is an index that accounts for the number and cover of invasive annual grasses (IAG) multiplied
by the ordinal deer and goose impact score (DG). The impact index is normalized by the greatest values
so all values are between 0 and 1. Area is the Log10 hectares of each island.
Component

166

Table A3-2. Model comparison table of 31 candidate models explaining the probability of plant
extirpation across 13 islands in the southern San Juan Island archipelago. LOOIC is the leave-one-out
cross-validation information criterion and its standard error, the smaller the value the better relative
fit. W is the model weight (the probability the model is the optimal model) based on Bayesian stacking
of the posterior-predictive densities of each model. Thus, models with the greatest weights have the
lowest relative predictive error. R2 is the variance of each model’s predictions divided by the
prediction variance and the expected error variance, interpretation is roughly analogous to the classical
R2 value. Bolded models comprise  90% of model weights. For explanation of Model abbreviations
see * in Table A3-1. * values in parenthesis denote refitted model weights when only considering the
top four models.
Model

LOOIC

w*

R2Fixed

R2Random

(N*A)+(N*Inc)+(N*Per)+(N*Cov)

239.67 (23.06)

0.06 (0.42)

0.48

0.13

(N*Cov)+(N*A)

243.25 (23.21)

0.07 (0.38)

0.46

0.15

(N*Inc)+(N*A)

249.68 (23.41)

0.051 (0.20

0.42

0.17

(N*Per)+(N*A)

261.69 (24.28)

0.00 (0.00)

0.4

0.19

N+A+Inc+Per+Cov

405.9 (29.1)

0.112

0.34

0.11

N+Inc+Per+Cov

406.29 (29.14)

0.109

0.33

0.12

(N*Inc)+(N*Per)+(N*Cov)

407.98 (29.72)

0.118

0.34

0.11

A+(N*Impact)+Inc+Per+Cov

409.99 (29.52)

0.002

0.34

0.04

(N*A)+(N*Impact)+(N*Inc)+(N*Per)+(N*Cov)

411.68 (29.86)

0.087

0.35

0.03

N*Cov

412.4 (30.22)

0.142

0.32

0.14

N+Cov

413.7 (29.88)

0.00

0.32

0.16

N+A+Cov

414.02 (29.91)

0.00

0.32

0.14

(N*Impact)+Cov

416.92 (29.94)

0.00

0.32

0.09

N+Inc

418.49 (29.61)

0.00

0.3

0.2

N+A+Inc

418.62 (29.74)

0.00

0.31

0.18

(N*Impact)+(N*A)+(N*Cov)

418.68 (30.71)

0.00

0.33

0.04

(N*Impact)+Inc

418.76 (29.98)

0.109

0.31

0.13

N*Inc

420.53 (29.97)

0.00

0.3

0.2

(N*Impact)+(N*A)+(N*Inc)

424.49 (30.63)

0.00

0.31

0.08

N*Per

428.9 (30.63)

0.077

0.28

0.23

N+Per

429.14 (30.59)

0.00

0.28

0.23

(N*Impact)+Per

430.09 (30.9)

0.021

0.29

0.16

N+A+Per

430.17 (30.87)

0.00

0.28

0.21

N

430.94 (30.64)

0.00

0.28

0.27

A+N

431.47 (30.74)

0.00

0.28

0.24

(N*Impact)+A

431.79 (30.83)

0.00

0.29

0.12

Impact

431.94 (30.91)

0.00

0.29

0.17

(N*Impact)+(N*A)+(N*Per)

432.41 (31.43)

0.04

0.29

0.1

N*A

433.81 (30.91)

0.00

0.28

0.23

Impact+Area

434.44 (31.02)

0.00

0.29

0.12

(N*Impact)+(N*A)

434.82 (31.14)

0.00

0.29

0.12

167

Figure A3-1. Predicted influence of the synergistic impact of IAG, geese and deer on the extirpation
probability of alien and native plants. Error bands represent 90% credible intervals.

168

Table A3-3. The number of colonization and extirpation events among native and alien vascular
plants across 14 islands along the Southern end of the San Juan Island archipelago.

Nativity
Alien

Taxon
Bromus sterilis
Cerastium pumilum
Vulpia myuros
Vicia sativa
Cakile maritima ssp. maritima
Senecio vulgaris
Polygonum aviculare
Rosa rubiginosa
Spergularia rubra
Vulpia bromoides
Sonchus oleraceus
Plantago lanceolata
Aira caryophyllea var. caryophyllea
Erodium cicutarium
Hypochaeris radicata
Sonchus asper ssp. asper
Cakile edentula
Cardamine hirsuta
Cerastium glomeratum
Dactylis glomerata
Geranium dissectum
Gnaphalium uliginosum
Hordeum murinum
Ilex aquifolium
Lepidium latifolium
Poa annua
Poa pratensis
Polypogon monspeliensis
Rumex crispus
Schedonorus arundinaceus
Silene gallica
Stellaria pallida
Aira praecox
Oxybasis rubra
Stellaria media
Taraxacum officinale

Colonized
4
4
4
3
2
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

Extirpated

2
2
1

3
2
1
1
1
1

2
2
2
2
169

Nativity

Taxon
Atriplex patula
Atriplex prostrata
Brassica juncea
Bromus hordeaceus
Cerastium fontanum ssp. vulgare
Cirsium vulgare
Geranium molle
Leontodon autumnalis
Malus domestica
Rumex acetosella
Sonchus arvensis
Spergularia salina
Taraxacum erythrospermum
Veronica arvensis

Colonized

Extirpated
1
1
1
1
1
1
1
1
1
1
1
1
1
1

Native
Polygonum spergulariiforme
Claytonia exigua
Plantago maritima
Aphyllon californicum ssp. californicum
Polystichum munitum
Shepherdia canadensis
Trifolium willdenovii
Achillea millefolium
Claytonia perfoliata
Spergularia macrotheca var. macrotheca
Atriplex dioica
Festuca rubra
Hordeum brachyantherum
Hornungia procumbens
Malus fusca
Montia fontana
Opuntia fragilis
Vicia hirsuta
Brodiaea coronaria
Claytonia rubra
Conioselinum pacificum
Grindelia hirsutula
Luzula subsessilis
170

1
1

1
1
1

1
1
1
1
1

4
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
1

Nativity

Taxon
Maianthemum stellatum
Trifolium microdon
Acer glabrum var. douglasii
Agrostis exarata
Amelanchier alnifolia
Armeria maritima ssp. californica
Berberis aquifolium
Bromus pacificus
Cerastium arvense ssp. strictum
Chamaenerion angustifolium
Collinsia parviflora
Elymus glaucus
Festuca roemeri
Fritillaria affinis
Galium aparine
Gaultheria shallon
Heuchera micrantha
Hordeum depressum
Lepidium virginicum ssp. menziesii
Leymus mollis ssp. mollis
Lomatium utriculatum
Lupinus microcarpus var. microcarpus
Oxytropis campestris var. spicata
Pentagramma triangularis
Platanthera elegans ssp. elegans
Platanthera unalascensis
Plectritis congesta
Polygonum fowleri ssp. fowleri
Polypodium glycyrrhiza
Potentilla anserina
Pseudognaphalium stramineum
Pseudotsuga menziesii var. menziesii
Puccinellia nutkaensis
Quercus garryana var. garryana
Ranunculus californicus × R. occidentalis
Ribes divaricatum var. divaricatum
Rubus nutkanus
Sabulina macra
Sanicula bipinnatifida

Colonized Extirpated
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
171

Nativity

172

Taxon
Sarcocornia pacifica
Sedum lanceolatum
Sedum spathulifolium
Sisyrinchium idahoense
Trifolium variegatum
Triphysaria pusilla
Turritis glabra
Vicia americana var. americana
Juncus bufonius
Plagiobothrys scouleri
Sambucus racemosa var. arborescens
Ambrosia chamissonis
Bromus sitchensis var. sitchensis
Distichlis spicata
Holodiscus discolor
Lathyrus japonicus
Lathyrus nevadensis var. nevadensis
Ranunculus californicus
Ribes sanguineum var. sanguineum
Sagina decumbens ssp. occidentalis
Sagina maxima
Salix scouleriana
Sanicula crassicaulis

Colonized

2
2
2
1
1
1
1
1
1
1
1
1
1
1
1

Extirpated
1
1
1
1
1
1
1
1