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Policy Alternatives for English Ivy Management in Washington State

Item

Title (dcterms:title)

Eng Policy Alternatives for English Ivy Management in Washington State

Date (dcterms:date)

2013

Creator (dcterms:creator)

Eng Baur, Alison

Subject (dcterms:subject)

Eng Environmental Studies

extracted text (extracttext:extracted_text)

POLICY ALTERNATIVES FOR ENGLISH IVY MANAGEMENT IN
WASHINGTON STATE

by
Alison Baur

A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
June 2013

©2013 by Alison Baur. All rights reserved.

This Thesis for the Master of Environmental Studies Degree
by
Alison Baur

has been approved for
The Evergreen State College
by
________________________
Dr. Dina Roberts
Member of the Faculty

________________________
Date

ABSTRACT
Policy Alternatives for English Ivy Management in Washington State
Alison Baur
Previous invasive species research has utilized expert opinion surveys to
determine optimal economic policies for an agricultural pest and to identify policy
preferences for horticultural invasive species. The purpose of this study is to
explore the efficacy of expert opinion surveys as a research tool for analyzing
policy alternatives for a specific horticultural invasive plant species. Weed board
and natural resource professionals in Washington State responded to survey
questions regarding the effectiveness, cost-effectiveness, and political feasibility
of policies for managing English ivy (Hedera spp.), a horticultural invader
threatening forest ecosystems in western portions of the state. Comparing
favorable and unfavorable responses for a series of policy alternatives using a
Chi-square test elucidated the policies garnering the highest degree of consensus.
The policy alternative regarding education and localized control efforts (policy 1)
received the highest ranking for all three evaluation criteria. The second most
highly-favored policy option was voluntary curtailment of English ivy sales in
nurseries (policy 4). Although results for cost-effectiveness and political
feasibility were similar between policies 1 and 4, the proportion of favorable
responses for the effectiveness of policy 4 was significantly lower than for policy
1 (χ2=13.48, p<0.001). Future research could utilize focus groups or follow-up
surveys to explore the rationale for policy preferences as well as establish
implementation details for the most favorable policy.

Table of Contents
1. Literature Review………….…………………………………………………...1
Invasion Ecology………………………………………………….……....4
Anthropogenic Dispersal……….…………………………………………9
Bioeconomics…………………………………………………..…….…..11
Risk Assessments……………………………………………….…….….14
Invasive Species Management…………………………………….……..16
Management Ethics……………….……………………………………...18
Invasive Species Policy…….…………………………………………….22
Future Work……………………………………………………………...25
Literature Cited………...………………….……………………………..27
2. Analyzing Invasive Species Policies with Expert Opinion Surveys: A Case
Study of English Ivy in Washington State……………………...………………..31
Introduction………………………..………………………………..........31
English Ivy……………………………………….…………………........34
Methods………………………………………………………….………37
Results……………………..………………………………….………….39
Discussion………………………………………………………………..48
Conclusion……………………………………………………………….54
Appendices.………………………………………………………….......56
Literature Cited…………………………………………………………..65
3. Research Significance and Future Directions………………………….…..….67
Literature Cited…………………………………………………………..71

iv

List of Figures
Figure 1.1. Climbing English ivy………………………………………………….2
Figure 1.2. English ivy (Hedera spp.) in its juvenile stage……………………….5
Figure 1.3. English ivy (Hedera spp.) in its adult stage…………………………..7
Figure 1.4. The Washington State Department of Agriculture English ivy
distribution
map………………………………………………………………………………..9
Figure 2.1. Influences on horticultural invasive species dispersal and policy
alternatives……..…………………………………………………………….......32
Figure 2.2. Responses from natural resource and weed board professionals in
Washington State regarding the effectiveness of policy alternatives for English
ivy management……………………………………………………………..…...45
Figure 2.3. Responses from natural resource and weed board professionals in
Washington State regarding the cost-effectiveness of policy alternatives for
English ivy management………………………………………………………....46
Figure 2.4. Responses from natural resource and weed board professionals in
Washington State regarding the political feasibility of policy alternatives for
English ivy management………………………………………………………....47
Figure 2.5. Ordination comparing survey responses of natural resource and weed
board professionals regarding English ivy’s relative importance in management
porftolios (top 5, top 10, top 25, top 50, or not a priority) according to geographic
management range (state=1, county=2, city=3, other=4) (A=0167,
p<0.001)………………………………………………………………………….60

v

List of Tables
Table 2.1. Responses from natural resource and weed board professionals in
Washington State regarding the importance of English ivy in their invasive
species management
portfolios…………………………………………………………………………40
Table 2.2. Responses from natural resource and weed board professionals in
Washington State regarding the importance of volunteers in their English ivy
removal efforts. The surveys were conducted in February and March of
2013……………………………………………………………………………...40
Table 2.3. Responses from natural resource and weed board professionals in
Washington State regarding factors strongly influencing the spread of English
ivy………………………………………………………………………………..41
Table 2.4. Responses from natural resource and weed board professionals
regarding the effectiveness of statewide policy alternatives in limiting the spread
of English ivy in Washington State……………………………………………...56
Table 2.5. Responses from natural resource and weed board professionals
regarding the cost-effectiveness of statewide policy alternatives in limiting the
spread of English ivy in Washington State……………………………………....57
Table 2.6. Responses from natural resource and weed board professionals
regarding the political feasibility of statewide policy alternatives in limiting the
spread of English ivy in Washington
State……………………………………………………………………..………..58
Table 2.7. The most common responses from natural resource and weed board
professionals regarding the effectiveness, cost-effectiveness, and political
feasibility of policy alternatives for English ivy management as well as Chisquare comparisons with the most popular policy (Policy
1)…………………………………………………………………………………59

vi

Acknowledgements
I would like to thank my thesis reader, Dr. Dina Roberts, and the other
MES faculty for sharing their diverse, interdisciplinary perspectives on
environmental issues. Thanks to Alison Halpern (Washington State Noxious
Weed Board) for all of the guidance and information. I also want to thank Dr.
Sarah Reichard (University of Washington) for writing fascinating research
papers on horticultural invaders and for fielding my questions on English ivy and
surveys. I sincerely appreciate Kory Kramer’s assistance in providing survey
contact information and data regarding the Green Cities Partnership’s English ivy
removal efforts. Ray Willard (Washington State Department of Transportation)
and Tom Wessels (Washington State Department of Agriculture) both provided
extremely helpful information on the state’s approach to English ivy management.
I would like to thank all of the natural resource and weed board professionals who
responded to my survey. Big thanks to Phil Riveness, Jen Riveness, Will Baur,
Katie Wolt, and Robyn Andrusyszyn for advice and editing.

vii

1. Literature Review
Non-native invasive species are organisms introduced from outside a
region that disperse rapidly without direct human assistance (Evans et al. 2008).
Invasive plants in Washington State can negatively impact ecological
communities and cause millions of dollars in damage. Statewide management
efforts prioritize new invaders that are not widely-distributed throughout the state
and could pose a major threat to public health, ecological communities, and local
businesses (NWCB 2010b). County weed boards, local governments, and
nonprofit organizations often opt to control a number of widespread invaders in
addition to the state’s designated priority species.
English ivy (Hedera helix and Hedera hibernica) is an invasive species in
western Washington that disrupts ecological processes. Climbing English ivy,
sometimes reaching up to 90 feet, can add considerable weight to trees (Figure
1.1) (Waggy 2010). Ivy can cover up tree leaves and hinder the process of
photosynthesis (Swearingen and Diedrich 2006). English ivy can also host
bacterial leaf scorch (Xylella fastidiosa), a pathogen harmful to many native tree
species (Swearingen and Diedrich 2006). Tree stress and death leads to public
safety hazards in the form of falling trees and branches. Tree losses also reduce
arboreal ecosystem services, such as air purification, stormwater infiltration, and
aesthetics.



The common name for Hedera hibernica is Irish ivy but most natural resource managers in
Washington State continue to refer to all invasive ivy as English ivy.

1

English ivy’s contribution to tree death causes gaps in forest canopies and
impacts understory communities (Waggy 2010). In a study of Seattle Parks,
Dlugosch (2005) observed that areas with English ivy had a smaller percent cover
of native species than non-invaded areas. Some studies indicate English ivy may
increase soil nitrogen levels at the expense of native plants reliant on low-nutrient
conditions (Waggy 2010). The displacement of native shrubs and young trees
likely reduces food and shelter for native fauna. Okerman (2000) employs the
term “ivy deserts” to describe English ivy monocultures in forest ecosystems.

Figure 1.1. Climbing English ivy. Climbing ivy can cause stress to trees
(left). Cutting ivy at the base of trees kills ivy in the canopy (right).
Photos: Alison Baur

2

Urban restoration efforts focus heavily on English ivy removal;
meanwhile, the plant’s reintroduction continues through horticultural practices.
This study investigates the effectiveness, affordability, and political feasibility of
policy alternatives to manage English ivy through a review of academic literature
and a survey to natural resource and weed board professionals.
There are numerous components involved in an invasive species policy
analysis:
1)

Species, habitat, or pathway characteristics contributing to
invasion success;

2)

Economic costs of invasive species and regulatory mechanisms;

3)

Risk assessment protocols for prioritizing management;

4)

Benefits and drawbacks of management strategies;

5)

Ethical dilemmas associated with management;

6)

And current international, federal, and state-level policies.

This literature review takes an interdisciplinary approach to invasive species
policy considerations drawing from the fields of invasion ecology, restoration
ecology, population biology, geography, economics, political science, and
philosophy. The scope of research ranges from general examinations of invasive
species to English ivy-specific studies.

3

Invasion Ecology
A number of studies investigate the life history traits intrinsic to invasive
species. Reichard and Hamilton (1997) used classification tree and discriminate
analyses to create a hierarchical predictive model of woody plant invasiveness.
The results suggested that the primary determinant of invasion success is whether
or not a plant invaded elsewhere; key traits include perfect flowers (containing
both stamens and carpels), vegetative reproduction, and a lack of pre-germination
requirements (Reichard and Hamilton 1997). Pyšek and Richardson (2007) also
examined invasive characteristics. The authors reviewed 18 academic studies and
determined that rapid growth, high fecundity, and large specific leaf area are
common attributes among invasive plants (Pyšek and Richardson 2007).
English ivy demonstrates many characteristics intrinsic to invaders. While
originally from Eurasia, English ivy is now invasive to parts of South America,
Australia, New Zealand, and 27 states in the United States (Invasive Species
Specialist Group 2005). The species reproduces copiously, exhibiting vegetative
growth in its juvenile stage (Figure 1.2.) and sexual reproduction as an adult
(Figure 1.3.) (Waggy 2010). Broken pieces of its stems or roots can grow
independently (Swearingen and Diedrich 2006). English ivy has perfect flowers
(Waggy 2010). The pre-germination requirements of English ivy seeds remain
unclear, but it is likely the seeds must go through scarification within avian
digestive tracts to achieve viability (Waggy 2010). In a review of English ivy
studies, Waggy (2010) found that the plant’s growth rates vary by habitat type but
tend to increase in moist areas. Ivy’s climbing ability permits its leaves to
4

increase photosynthesis with closer proximity to sunlight (Waggy 2010). English
ivy’s life history characteristics contribute to its competitive advantage over many
native plant species.

Figure 1.2. English ivy (Hedera spp.) in its juvenile stage.
Photo: Alison Baur

Concepts from population biology explain the process of ecological
invasions. The novel weapons hypothesis elucidates how certain invaders alter an
environment to suit their needs (Hufbauer and Torchin 2007). An example of a
novel weapon is allelopathy, or a plant’s ability to alter soil chemistry at the
detriment of other species. While some research indicates English ivy increases
soil nitrogen levels, other studies question its overall allelopathic effects.
Biggerstaff and Beck (2007a) determined English ivy had a minimal allelopathic
impact on the regeneration of lanceleaf coreopsis (Coreopsis lanceolata), a
5

wildflower common to the southeastern United States. Another novel weapon is
the moderate toxicity of English ivy’s leaves and fruit (Swearingen and Diedrich
2006). The glycoside hederin toxin in ivy berries increases the likelihood birds
will regurgitate the seeds and facilitate dispersal (National Park Service 2010).
A second population biology theory pertaining to invasions is the “empty
niche hypothesis”. The hypothesis infers that a habitat with less species diversity
is more prone to invasion because invaders capitalize on underutilized resources,
including sunlight, soil nutrients, or water. Hufbauer and Torchin (2007) claim
the hypothesis explains some invasions better than others. Interactions between
species in an ecosystem also influence the invasion process. Invaders often take
advantage of mutualists, such as pollinators, in a process known as invasional
meltdown (Hufbauer and Torchin 2007). Wasps, bees, and flies all pollinate
English ivy flowers (Invasive Species Specialist Group 2005). Dispersers of
English ivy seeds include Cedar Waxwings (Bombycilla cedrorum), American
Robins (Turdus migratorius), Stellar Jays (Cyanocitta stelleri), Mockingbirds
(Mimus spp.), European Starlings (Sturnus vulgaris), and House Sparrows (Passer
domesticus) (Swearingen and Diedrich 2006). As a primary consumer of English
ivy berries, European Starlings are also invasive and often out-compete native
bird species (Waggy 2010).
Genetics are another factor in the invasion process. Sakai et al. (2001)
explain that limited genetic diversity among introduced species at first hinders
population growth due to bottleneck effects and genetic drift. With greater
propagule pressure (frequency and magnitude of introductions), genetic diversity
6

increases within a population, making it more resilient (Sakai et al. 2001). In a
study of primrose (Primula vulgaris Huds.) in Belgium, Endels and authors
(2007) found that larger populations were more viable, even when confronting
genetic and environmental stochasticity.

Figure 1.3. English ivy (Hedera spp.) in its adult stage.
Photo: Alison Baur

English ivy’s phenotypic plasticity (genetic adaptability) contributes to its
invasion success. There are 13 species and 400 cultivars of Hedera, although not
all are considered invasive (Clarke et al. 2006). Clarke and colleagues (2006)
analyzed the taxonomic identity of 58 Hedera populations in Oregon,
Washington, and British Columbia. Genetic profiles revealed 85 % of the
sampled ivy was H. hibernica and 15% was H. helix “Calfornia”, “Pittsburgh”,
“Star” or other hybrids (Clarke et al. 2006). The authors claim many invasive
7

English ivy cultivars derived from hybridization and mutation (Clarke et al.
2006).
In addition to the invader’s traits and ecological interactions, another
contributor to invasion success is landscape structure. In a comparison of the
spatial distributions of invasive and non-invasive alien plants in California, Dark
(2004) identified exotic species most often in regions with low elevations, high
road density, and high native plant species richness. Roads likely increase
invasive plant dispersal by acting as corridors for plant and seed transport
(Kowarik and von der Lippe 2007). A combination of natural and anthropogenic
landscape features can serve to predict the likelihood of invasion in a particular
location.
Similarly, studies investigate the environmental factors pertaining to
English ivy’s distribution. In California, English ivy favors elevations below
3,300 feet (Waggy 2010). The presence of English ivy correlates with areas of
high road density, such as urban and suburban forests (Clarke et al. 2006). In
Washington State, the Noxious Weed Control Board (NWCB) describes ivy
habitat as landscaped areas, disturbed forests, fields, hedgerows, and coastal areas
(NWCB 2010a). The Washington State Department of Agriculture’s English ivy
distribution map indicates that ivy is most common west of the Cascade Mountain
Range (Figure 1.4.).

8

Figure 1.4. The Washington State Department of Agriculture (WSDA) English
ivy distribution map.
Retrieved from http://www.nwcb.wa.gov/siteFiles/English%20Ivy%202011.pdf

Anthropogenic Dispersal
Non-native species introductions have occurred throughout history, but
current rates are unprecedented due to globalized trade and travel (Ielmini et al.
2012). Ecologist Gordon Orions coined the term “homogocene” to describe the
extensive anthropogenic dispersal of species (Ielmini et al. 2012). Kowarkik and
von der Lippe (2007) claim an understanding of dispersal vectors according to
9

human motivation is helpful for invasive species management. Various studies
identify anthropogenic drivers of invasive species dispersal including trade,
disturbance, bureaucratic land use incentives, and preferences for utilitarian and
medicinal plants (Meyerson and Mooney 2007, Robbins 2004). In a two-year
experimental study of understory plants in a riparian forest, Von Holle and
Simberloff (2005) determined that propagule pressure (frequency and magnitude
of introductions) is a significant determinant of invasion success (Von Holle and
Simberloff 2005). Horticulture is a major anthropogenic pathway, accounting for
more than 50% of wildland invaders and 80% of woody invasive species
(Reichard 2011).
The human facilitation of English ivy dispersal often occurs through
horticultural practices. English ivy is a popular ornamental plant because it is
low-maintenance, hardy, and evergreen (Swearingen and Diedrich 2006).
According to the NWCB (2001), colonial settlers brought English ivy to the
United States in 1727 and to the Pacific Northwest sometime before 1890. Clarke
and colleagues (2006) found that regional nursery catalogs between 1915 and
1968 advertised eight common invasive ivy cultivars (Clarke et al. 2006). The
Washington State Department of Transportation actively planted English ivy
along Interstate 5 (the major north-south corridor) in the 1960s through the 1990s,
contributing to its dispersal throughout the western portion of the state (Ray
Willard, personal communication 2013). Gardening associations, such as the
American Ivy Society, continue to value ivy as a component in English-style
gardens. The American Ivy Society’s designated “Ivy of the Year” for 2013,
10

Hedera helix, is invasive to the Pacific Northwest (American Ivy Society, Inc.
2013).
Bioeconomics
The anthropogenic spread of invasive species has economic implications.
The Nature Conservancy (2013) estimates global costs of invasive species amount
to $1.4 trillion. Pimentel et al. (2005) claim costs to the U.S. economy are around
$120 billion. Critics argue that estimates of economic impacts, specifically the
calculations of Pimentel et al., conflate calculations of damages and costs, use
outdated information, present one-time costs as recurring, and do not consider the
potential economic benefits of invasive species (Sagoff 2009). Another method
of identifying direct economic costs is to examine invasive species management
budgets. The Washington State Department of Transportation spent about $4.5
million in 2011 to combat noxious weeds on its properties (NWCB 2012). The
Washington State Legislature allocated $913,173 in the 2009-2011 biennium to
support NWCB and Washington State Department of Agriculture invasive species
management efforts (NWCB 2012). The Green Cities Partnership, a coalition
coordinated by the nonprofit land trust, Forterra, spent about $1.2 million in 2011
on program staff, contracts, and supplies to support volunteer efforts to remove
ivy and other invasive species in the cities of Seattle, Tacoma, Redmond, Everett,
and Kirkland (K. Kramer, personal communication, May 6, 2013). In addition to
monetary costs, the organization estimates volunteer involvement at ivy removal
events amounted to 16,000 hours (K. Kramer, personal communication, May 6,
2013).
11

An emerging field of study, known as bioeconomics, integrates biological
factors into economic analyses (Keller et al. 2009). According to Keller and
colleagues (2009), the purpose of a bioeconomic model is to “help society design
incentive mechanisms that better satisfy political objectives, meet species
biological needs, and protect private property concerns”. A number of studies
utilize bioeconomic models to determine the economic impacts of invasions.
McIntosh et al. (2009) describe the importance of considering long-term
ecological, economic, and social costs and benefits of a given management
response as well as prioritizing limited natural resource funding (McIntosh et al.
2009). For example, managing invasive ornamental species can result in forgone
economic benefits to nurseries. The authors also claim policymakers should
recognize the opportunity cost of spending public money on invasive species
management (McIntosh, et al. 2009). Washington State lawmakers allocate about
1% of the operating budget to natural resource management, only a portion of
which is spent on invasive species control (Office of Program Research 2011).
The majority of the state’s budget goes to education and social services (Office of
Program Research 2011). In addition to direct costs and benefits, a bioeconomic
model can reflect indirect costs, such as losses of ecosystem services. Cook et al.
(2007) estimated that efforts to prevent a varroa bee mite invasion in Australia
would likely save the country $27.5 million per year in pollination services (Cook
et al. 2007). Bioeconomics often involves complex models that incorporate both
direct and indirect costs and benefits of a given policy as well as the opportunity
costs.

12

An impediment to the widespread use of bioeconomic modeling is the lack
of quantitative data on the distribution and impacts of individual invaders.
Eiswerth and van Kooten (2002) utilized surveys and a stochastic dynamic
programming model to identify economically optimal management decisions for
yellow starthistle (Centaurea solstitialis) in California rangelands. The authors
explored expert opinion through surveys of weed scientists, county farm advisors,
and public land managers, and subsequently concluded that long-term
management of yellow starthistle is the best option (Eiswerth and van Kooten
2002). The survey results coupled with economic modeling effectively addressed
the lack of quantitative data on the cost-effectiveness of invasive species
management strategies.
There are numerous economic instruments for reducing invasions. One
approach is to tax nurseries selling invasive species. Knowler and Barbier (2005)
created a model to obtain a social optimum of introductions through an
“introducer pays” tax. The model factored in social costs and benefits, plant
characteristics, and the number of nurseries (Knowler and Barbier 2005). The
authors concluded that a tax may moderately reduce the number of nurseries
depending on the invasion risk level acceptable to a given community (Knowler
and Barbier 2005). A study by Barbier et al. (2013) surveying horticultural and
weed specialist stakeholders revealed an overall preference for mandatory
screening and banning of likely invaders over nursery industry fees. The authors
determined that nursery industry opposition and uncertainty surrounding invasive
species impacts pose implementation challenges for economic policy instruments
13

(Barbier et al. 2013). In both cases, the viability of taxation as policy option
depended on stakeholder values.
In addition to taxes and fees, other potential economic instruments for
managing horticultural invaders include import tariffs, tradable permits, graduated
license fees, and environmental bonds. The World Trade Organization’s (WTO)
Sanitary and Phytosanitary Agreement requires countries to assess the likelihood
of ecological and economic damage as well as the costs of control prior to
implementing import restrictions and tariffs (Powell 2004). A tradable permits
system based on invasion risk would be complex, data-heavy, and dependent on
heterogeneity among target species (Touza, Dehnen-Schmutz, and Jones 2007).
The graduated license fee approach requires higher fees from nurseries
contributing greater invasion risk (Touza, Dehnen-Schmutz, and Jones 2007). An
environmental bond is a sum based on future projected invasion risk that is
charged to nurseries but returned upon demonstrated reductions in invasive
species dispersal (Touza, Dehnen-Schmutz, and Jones 2007). These alternative
economic policy instruments are not yet widely used and merit further research.
Risk Assessments
Risk assessments can be helpful tools to determine potential invasive
species impacts. There are a number of variations on risk assessments that
consider different inputs. For example, the Washington Invasive Species Council
(2009) utilizes a risk assessment model comparing prevention feasibility to an
invader’s environmental, economic, and human health impacts (Washington

14

Invasive Species Council [WISC] 2009). The Council uses the data to calculate
an impact score which informs the appropriate management response (WISC
2009). The Council applied its model to 50 priority invasive plant and animal
species, but English ivy was not among them (WISC 2009). Various academic
studies recommend risk assessments consider climate suitability, habitat
availability, points of entry, and propagule pressure (Hulme 2009); incorporate
molecular techniques to identify and disrupt introduction pathways (Simberloff et
al. 2005); and delineate potential invasion impacts on ecological connectivity
(Stohlgren and Jarnevich 2009). Powell (2004) describes the need for a more
quantitative approach to risk assessments in order to comply with world trade
agreements.
A number of studies identify ways to evaluate risk assessment procedures.
Costello et al. (2007) claim the evaluation of an invasive species prevention
program must consider the lag time between a species’ introduction and its
establishment because it may take years for the benefits of prevention measures to
materialize. Keller and authors (2007) examine the net economic costs and
benefits of Australia’s risk assessment protocols with a discount rate of 10-15
years. The authors conclude that the Australian risk assessment program
produces net economic benefits, especially long-term (Keller et al. 2007). Risk
assessment evaluation over the course of many years can reveal whether
prevention measures achieve projected outcomes.

15

Invasive Species Management
Invasive species management strategies include prevention, eradication,
and control. Early detection and prevention are the most cost-effective ways to
limit invasive species dispersal. Reichard (2004) explains how horticultural
industries could prevent invasions by implementing “voluntary codes of conduct”
to curtail invasive plant sales and educate the public. In a prior study, Reichard
and White (2001) examine the efficacy of educational outreach as a prevention
tool. Through surveys to horticultural customers, the authors found that
individuals educated on invasive species are less likely to purchase horticultural
invaders (Reichard and White 2001). Holt (2009) describes how practical
measures, such as weed-free landscaping products and clean equipment, prevent
the spread of invasive species into restoration areas. Quarantines or weed laws
are another potential of prevention (Holt 2009). Although prevention measures
are often the most cost-effective approach to management, Finnoff et al. (2005)
found that risk-averse managers more often choose control over prevention
because positive results appear more guaranteed (Finnoff et al. 2005).
Another management option is to remove invasive species once they have
become established. If an introduced population is small enough and reintroduction risk is minimal, then eradication is often a cost-effective option, even
if initial costs are high (Genovesi 2007). According to Genovesi (2007),
eradication is more difficult for flora than fauna because plants have “a dormant
life stage, high dispersal capacity, and high reproduction”. If the invader is
already widespread, resource managers may choose to control it just enough to
16

maintain agricultural and ecological functions (Holt 2009). Articles by Holt
(2009) and Simberloff et al. (2005) describe the utility and drawbacks of control
methods. In order to successfully control a species, resource managers should
understand its biology and utilize techniques that cause the least ecological
disruption (Simberloff et al. 2005). In addition, resource managers must have
legal grounds for management, adequate funding, and stakeholder cooperation
(Simberloff et al. 2005). Manual or mechanized removal can be an effective but
labor-intensive control strategy (Holt 2009). Herbicides are also often effective
but are controversial when harmful to non-target organisms (Simberloff et al.
2005). Introducing biological control agents, such as insects that eat the invasive
plant, is contentious because the species are often non-native and can have
unintended ecological impacts. There are currently no known biological control
agents for English ivy (Waggy 2010); manual removal is the most common
English Ivy control strategy (personal observation).
In a study of English ivy control methods, Biggerstaff and Beck (2007b)
examined the effectiveness of manual removal and herbicide. In some treatment
plots, the researchers sowed native seeds after applying removal treatments
(Biggerstaff and Beck 2007b). Two months later, Biggerstaff and Beck (2007b)
measured the number of germinated seedlings, seedling density, and species
richness. The results indicated that pulling ivy allowed for the greatest seedling
density and diversity with and without seed addition (Biggerstaff and Beck
2007b). Spraying effectively removed ivy but resulted in lower seedling density
and diversity, possibly because the ivy root structure remained intact and inhibited
17

germination (Biggerstaff and Beck 2007b). In plots where Biggerstaff and Beck
left English ivy in place, no seeds germinated (Biggerstaff and Beck 2007b). The
authors concluded that hand pulling English ivy and sowing native seeds is the
most effective management strategy (Biggerstaff and Beck 2007b).
Removing an invader does not always signify that the habitat will return to
its pre-invaded state. Biggerstaff and Beck (2007a) conducted a study
investigating restoration potential post-English ivy removal. Specifically, the
authors examined seed bank formation and germination (Biggerstaff and Beck
2007a). Research plots included areas where ivy was removed recently or three
years prior as well as non-invaded areas (Biggerstaff and Beck 2007a). After
monitoring the germination rates and species composition in soil samples over the
course of eight months, the authors found that English ivy did not diminish the
seed bank (Biggerstaff and Beck 2007a). The authors conclude that restoration
involving English ivy removal may succeed due to the paucity of negative
residual ecological impacts (Biggerstaff and Beck 2007).
Management Ethics
A moral argument for invasive species control contends that native species
have more intrinsic value than non-native species (Boorse 2004). The typical
definition of biodiversity in the United States applies only to species and
interactions present in North America prior to European settlement (Lodge and
Shrader-Frechette 2003). The Columbian benchmark denotes a time when
human-facilitated introductions of non-native species increased dramatically

18

(Lodge and Shrader-Frechette 2003). By distinguishing between anthropogenic
and “natural” introductions, proponents of invasive species control imply a
separation between humans and nature. Another ethical argument for invasive
species control is that certain invaders have negative impacts to public health, the
economy, and ecosystem services.
Individuals may morally oppose invasive species management because
they believe the introduction of novel organisms is natural and may even benefit
ecosystems and society. Some critics argue that anthropogenic introductions are
“natural” and the 1492 benchmark is irrelevant (Lodge and Shrader-Frechette
2003). However, Lodge and Shrader-Frechette (2003) argue that assuming
humans are part of nature and therefore everything they do is good equates to a
“naturalistic fallacy” and undermines the basis of civil society. Sagoff (2009)
claims invasive species do not generally lead to the extinction of native species
except on island-like habitats. When the spread of an invader does not cause
extinction, the introduced organism contributes to the overall species richness of
an ecological community and may even provide food or habitat for an endangered
species (Sagoff 2009). Once introduced to a new geographic range, an invasive
species can increase genetic diversity by diverging from its parent population
through mutations, genetic drift, and natural selection (Sagoff 2009).
Furthermore, as both native and non-native species assemblages shift due to
climate change, invasive species may be more adaptive to environmental change
and fill critical ecological niches (Thuiller et al. 2007). Anthropocentric

19

opponents of control may value invasive species as sources of food, medicine,
fiber, biofuel, or ornament.
An additional moral argument against management pertains to harmful
control strategies. Certain techniques, such as herbicide or biocontrol, may have
unintended consequences that negatively impact biodiversity. According to
Evans et al. (2008), exposure to herbicide can backfire if it leads to the natural
selection of herbicide-resistant invasive organisms. Killing a species directly or
indirectly raises ethical concerns about an individual species’ or population’s right
to life. Opponents would claim that the adverse consequences of management
strategies outweigh the benefits of controlling the spread an invader.
There are also ethical dilemmas when management infringes on private
property rights. While some may argue that private property autonomy is a
“right”, Bardach (2012) points out that “…rights are simply convenient tools of
social organization and rights-based claims, a consensually accepted way of
negotiating the changing landscape of whose interests should be protected to what
degree and with what exceptions.” It could be argued that the rights of some
members of society to house weeds on their properties infringes on the rights of
their neighbors to have weed-free properties. In Washington, the state noxious
weed board can require private property owners to control certain invaders.
Another moral debacle surrounds the role of scientists. Opponents of
scientific involvement in management argue that scientists should maintain
objectivity and avoid normative judgments about whether a species is “good” or

20

“bad” (Lodge and Shrader-Frechette 2003). Some authors argue that terminology,
such as “invasive”, “alien”, and “noxious”, is indicative of a xenophobic or
nationalistic bias within the scientific community toward non-native species
(Evans et al. 2008). Proponents of scientific involvement may claim that science
can never truly be objective and the pressing-nature of biological invasions merits
a decisive response from the scientific community.
Public involvement in policymaking can also raise ethical questions.
Proponents of greater participation assert that public involvement is an expression
of democratic ideals. Some believe public behavior is the primary cause of
invasive species introductions and is therefore necessary to the solution. Boorse
(2004) claims the effects of invasive species are locally-relevant and the public
can contribute localized expertise and monitoring. Evans and colleagues (2008)
suggest that public participation helps correct management pathologies, such as
policies universally eliminating all invaders regardless of impact. In contrast,
Bardach (2011) warns that more participation is not necessarily more democratic.
He claims people with more time, special interests, and/or ideologies often
dominate the participatory process (Bardach 2011). The dilemma with regard to
invasive species is that benefits of management are typically diffused while costs
are concentrated, so special interests are sometimes the most vocal. Sagoff (2009)
poses the dilemma that if invasive species management is meant to be scientific in
nature, then stakeholder involvement undermines the scientific process. On the
other hand, if invasive species management is political, then scientists should not
override the will of stakeholders (Sagoff 2009).
21

Invasive Species Policy
International, national, and state-level policies address invasive species
issues. In the international arena, the United Nations (UN) Convention on
Biological Diversity instructs contracting parties to prevent, eradicate, and control
invasive species (Convention on Biological Diversity 2013). The Convention
garnered 168 signatures between 1992 and 1993 (Convention on Biological
Diversity 2013). At the 7th Conference of the Parties, participants recognized
horticulture as a key pathway for invasive species introductions (Convention on
Biological Diversity 2013). The International Plant Protection Convention (IPPC)
is another UN treaty agreement coordinating invasive species management
strategies among nations (Clout and De Porter 2005). The World Trade
Organization (WTO) Agreement on the Application of Sanitary and Phytosanitary
Measures ensures invasive species risk assessments do not interfere with free
trade (Clout and De Porter 2005).
There are also a number of international invasive species partnerships.
The Invasive Species Specialist Group (ISSG), established in 1993, consists of
about 170 experts from more than 40 countries (Clout and De Porter 2005). Its
mission is to increase awareness about invasive species and offer policy advice to
the World Conservation Union (IUCN) (Clout and De Porter 2005). The Global
Invasive Species Program (GISP), is a partnership between the IUCN, the
Commonwealth Bureau of Agriculture – International (CAB-I), and the UN
Environmental Program (UNEP) (United Nations System-Wide Earthwatch
2002). Since its establishment in 1997, the group has published documents on
22

invasive species management, economics, and legislation (Clout and De Porter
2005). The partnership is currently coordinating a multi-disciplinary working
group of experts to encourage international capacity-building and cooperation
(Clout and De Porter 2005).
Federal policies pertain to invasive species research, funding, and
coordinated management among federal agencies. The United States government
created the Federal Interagency Committee for the Management of Noxious and
Exotic Weeds (FICMNEW) in 1990 to investigate the extent of the invasive
species problem and recommend necessary actions (Ielmini et al. 2012). In 1997,
the FICMNEW published a plan for federal invasive species response entitled
“Pulling Together – A National Strategy for Invasive Plant Management” (Ielmini
et al. 2012). President Clinton signed Executive Order 13112 in 1999 establishing
the National Invasive Species Council (NISC) to coordinate federal agency
programs (Ielmini et al. 2012). Currently, there are 23 federal agencies managing
invasive species in some capacity (Simberloff et al. 2005). In 2003,
environmental groups formed the National Environmental Coalition on Invasive
Species (NECIS) to provide scientific expertise and inform federal policy (Ielmini
et al. 2012). The group recently sent President Obama a request for tighter
invasive species regulations and additional funding to support research and
screening.
Washington State has its own invasive species policies. The legislature
established the Washington State Noxious Weed Control Board (NWCB) in 1975
with the intent to “limit economic loss and adverse effects to Washington's
23

agricultural, natural, and human resources …” (RCW 17.10.007). State weed
board members include representatives of county and district weed boards,
appointees of the directors of the Washington State Department of Agriculture
and the Washington State Association of Counties, and three non-voting scientific
advisors (NWCB 2012). The board maintains a weed list designating plants as
Class A, B, or C depending on their control requirements and distribution (NWCB
2010b). Class A weeds are new to the area and not widely distributed (NWCB
2010b). State law requires that public and private landowners extirpate Class A
weeds on their properties (NWCB 2010b). Class B weeds are widespread in some
areas of the state but not others (NWCB 2010b). The board’s prioritization
strategy is to reduce the abundance of Class B weeds and prevent them from
spreading into new areas (NWCB 2010b). Class C weeds are found throughout
Washington, and the weed board engages the public in education and outreach on
the impacts of those species (NWCB 2010b). County weed boards can opt to
require mandatory control for Class B and C species (NWCB 2010b). The
NWCB follows rule-making processes to amend the noxious weed list (WAC 17750). Before adding a species to the list, the NWCB considers public testimony
and the plant’s economic impact on small businesses.
Public involvement in invasive species policymaking can range from
passive forms of participation (i.e. town hall meetings) to active decision-making
(i.e. citizen task forces) (Boudejas 2009). Evans and authors (2008) recommend
citizen stakeholders and regulating agencies collaborate to develop matrices
outlining the pros and cons of managing a particular species. The authors also
24

advocate for the integration of public input and scientific experimentation, calling
the process “experimental pluralism” (Evans et al. 2008). Boorse (2004) notes
that although scientists and lands managers have increasingly focused on invasive
species in recent years, public awareness has not significantly changed. The
author hypothesizes that reasons for low public awareness include a limited public
understanding of ecology, a lack of invasive species educational materials,
uncertainty and rapid growth within invasion ecology research, and a diversion of
public attention to other issues (Boorse 2004). Many authors believe that when
the greater public is engaged with invasive species issues, management is more
effective.
Future Work
A number of studies in the scientific literature identify future needs for
invasive species research. Some authors (Meyerson and Mooney 2007,
Chornesky and Randall 2003) argue for more interdisciplinary collaboration to
understand and manage invasive species. Chornesky and Randall (2003) suggest
developing networked databases to notify officials when an invader expands its
distribution. Conservation and management across larger geographic areas would
better-protect ecological processes and populations of rare species (Chornesky
and Randall, 2003). Long-term research is needed to address the effects of
climate change (Chornesky and Randall, 2003, Thuiller et al. 2007). As
ecological assemblages change with climate alteration, conservationists may need
to reconsider the ecological role of invasive species (Chornesky and Randall
2003, Thuiller et al. 2007). Adopting an interdisciplinary approach and
25

broadening the spatial and temporal scales of research would greatly expand
current knowledge of invasive species issues.
Other knowledge gaps pertain to methodology for analyzing invasive
species policies. A major hurdle for policymakers is the lack of quantitative data
on the distribution and impacts of individual invaders. Previously mentioned
studies use expert opinion surveys to identify economically optimal management
strategies for an invasive plant (Eiswerth and van Kooten 2002) or stakeholder
preferences for various policies regarding horticultural invaders (Barbier et al.
2013). Combining these methodologies to identify the most effective, costeffective, and politically feasible policy for a particular invasive species could
offer practical information to guide management in a given location. The
research presented in Chapter 2 uses expert opinion survey methodology to
identify the most favorable and realistic English ivy policy alternatives in
Washington State.

26

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f

30

Chapter 2. Analyzing Invasive Species Policies with Expert Opinion
Surveys: A Case Study of English Ivy in Washington State
Introduction
Invasive species pose a major threat to biodiversity (Wilcove et al. 1998)
and cost the United States billions of dollars each year (Pimentel 2005).
Horticulture is a major anthropogenic pathway for invasive species introductions,
accounting for more than 50% of wildland invaders and 80% of woody invasive
species (Reichard 2011). The dilemma with regard to invasive species
policymaking is that public benefits of management are typically diffused while
costs are concentrated on certain stakeholders, such as plant nurseries. According
to Bardach (2012), “[policy] analysts should… speak up for the taxpayers whose
interests may be squeezed out by better-organized advocacy groups.” The failure
of the market to regulate social and environmental costs of horticultural invaders
merits policy intervention. This study offers a framework for analyzing invasive
species policy alternatives.
Bardach (2012) proposes that policy analyses define the policy problem,
assemble evidence, construct alternatives, select evaluative criteria, project
outcomes, and confront trade-offs before deciding on appropriate policy
alternatives. Despite some criticisms of invasive species control (see Sagoff
2009), this study assumes that management of certain invaders provides a net
benefit to society. The policy problem is therefore the preponderance of nonnative horticultural species reproducing without human assistance and causing

31

negative ecological and economic impacts. Based on a literature review and
expert opinion, this study incorporates a framework identifying causes of
horticultural invasions and potential policy alternatives (Figure 2.1). Although
there are potentially additional invasion influences and policy alternatives, the
framework presents common policy themes in invasive species literature. It is
important to note that the policy alternatives are not mutually exclusive;
policymakers can employ more than one to manage a particular invasive species.

Figure 2.1. Influences on horticultural invasive species dispersal and policy
alternatives. Arrows indicate when a policy alternative addresses an influential
factor.

Upon identifying the policy problem, the next step in policy analysis is to
gather evidence regarding the nature of the problem and possible solutions

32

(Bardach 2012). A common obstacle to evidence-gathering for invasive species
policies is the lack of quantitative data on the distribution and impacts of
individual invaders (Eiswerth and van Kooten 2002). Surveys of weed specialists
can offer key information in place of quantitative data. Previous studies have
utilized surveys to analyze invasive species policy options. For example,
Eiswerth and van Kooten (2002) surveyed experts, including weed scientists,
public land managers, and others, on the effectiveness of five alternative
strategies to control yellow starthistle (Centaurea solstitalis) in California. The
authors incorporated survey results into a stochastic dynamic programming model
to identify economically optimal management decisions (Eiswerth and van
Kooten 2002). A study by Barbier and authors (2013) surveyed horticultural
industry representatives, hobby gardeners, agriculturalists, park managers and
staff, invasive species experts, and conservationists across North America to
gauge preferences for bans, taxes, and fees. Both studies utilize surveys to gather
information on an invasive species problem and gauge preferences for policy or
management alternatives.
In addition to selecting policy alternatives and gathering evidence, another
step in the policy analysis process is to establish assessment criteria (Bardach
2012). In this study, there are three criteria: effectiveness, cost-effectiveness, and
political feasibility. Effectiveness refers to a policy’s ability to limit the future
dispersal of an invasive species. Cost-effectiveness pertains to the policy’s
impact given limited financial resources. While effectiveness and costeffectiveness are both evaluative, the third criterion is practical; political
33

feasibility judges whether a proposed policy faces too much opposition or garners
too little support (Bardach 2012). The goal of this study is to utilize an expert
opinion survey to identify the extent and causes of a specific invasion problem
and investigate the effectiveness, cost-effectiveness, and political feasibility of
various policy alternatives. The survey specifically addresses the English ivy
(Hedera helix and Hedera hibernica) invasion in Washington State.
English Ivy Characteristics
English ivy is a popular ornamental groundcover invasive to parts of
South America, Australia, New Zealand, and 27 states in the United States
(Invasive Species Specialist Group 2005). Native to Eurasia, colonial settlers
brought English ivy to the United States in 1727 and to the Pacific Northwest
sometime before 1890 (Washington State Noxious Weed Control Board [NWCB]
1999). The Washington State Department of Transportation actively planted
English ivy along Interstate 5 (a major north-south corridor) from the 1960s
through the 1990s, contributing to its dispersal throughout western portions of the
state (R. Willard, personal communication, April 3, 2013). Regional nursery
catalogs between 1915 and 1968 advertised eight common invasive ivy cultivars
(Clarke et al. 2006). Many nurseries in Washington State continue selling
invasive ivy.
English ivy occupies a variety of habitat types, but its horticultural origins
make it most common in urban landscapes. In Washington State, the Noxious


The common name for Hedera hibernica is Irish ivy but many natural resource managers in
Washington State refer to all invasive ivy as English ivy.

34

Weed Control Board describes ivy’s habitat preferences as landscaped areas,
disturbed forests, fields, hedgerows, and coastal areas (NWCB 2010a). In a
review of English ivy research, Waggy (2010) found that English ivy growth rates
vary by habitat but tend to increase in moist areas. The Washington State
Department of Agriculture distribution map indicates ivy is most common in the
temperate areas west of the Cascade Mountain Range (Washington State
Department of Agriculture 2011).
English ivy’s characteristics contribute to its invasion success. In its
juvenile stage, ivy spreads vegetatively (Waggy 2010). The plant uses rhizomes
and a sticky substance to climb surfaces in pursuit of sunlight (Waggy 2010).
When exposed to sun, its rate of photosynthesis increases and the plant transitions
into an adult life involving seed production (Waggy 2010). Dispersers of English
ivy seeds include Cedar Waxwings (Bombycilla cedrorum), American Robins
(Turdus migratorius), Stellar Jays (Cyanocitta stelleri), Mockingbirds (Mimus
spp.), European Starlings (Sturnus vulgaris), and House Sparrows (Passer
domesticus) (Swearingen and Diedrich 2006). The glycoside hederin toxin in ivy
berries increases the likelihood birds will regurgitate the seeds and facilitate
dispersal (National Park Service 2010). English ivy has perfect flowers (Waggy,
2010), and its pollinators are wasps, bees, and flies (Invasive Species Specialist
Group 2005). English ivy’s characteristics contribute to its competitive advantage
over many native plant species.
Another factor contributing to English ivy’s invasiveness is genetic
plasticity. High propagule pressure of English ivy over time enhanced the plant’s
35

genetic diversity and populations are now more robust. Clarke and colleagues
(2006) discerned that English ivy is morphologically variable and individual
cultivars can cross with more aggressive ones (Clarke et al. 2006). Based on 58
Hedera populations in Oregon, Washington, and British Columbia, the authors
discovered the majority of ivy was H. hibernica (85%) and the rest was H. helix
“California”, “Pittsburgh”, “Star” or other hybrids (Clarke et al. 2006). The
authors explain that many invasive English ivy cultivars derived from
hybridization and mutation (Clarke et al. 2006).
Invasive ivy has negative environmental and economic impacts. Climbing
English ivy, sometimes reaching up to 90 feet, can add considerable weight to
trees (Waggy 2010). Ivy can cover up tree leaves and hinder the process of
photosynthesis (Swearingen and Diedrich 2006). English ivy can host bacterial
leaf scorch (Xylella fastidiosa), a pathogen harmful to many native tree species
(Swearingen and Diedrich 2006). Tree stress and death lead to public safety
hazards, such as falling trees and branches. Tree losses also reduce arboreal
ecosystem services including air purification, stormwater infiltration, and
aesthetics. English ivy alters understory habitats through competition. When ivy
kills trees and forms an understory monoculture, it is called an “ivy desert”
(Okerman 2000). English ivy’s displacement of native shrubs likely reduces food
and shelter for native fauna.

36

Methods
Framework and Rationale of Survey Methodology
The methodological process for this study involved identifying the relative
importance of English ivy to weed specialists and determining appropriate policy
alternatives. Preliminary questions in the web-based survey pertained to the
respondent’s sector and scope of management. Next, survey respondents
indicated English ivy’s ranking in their management portfolios as well as the
importance of volunteers in their ivy removal efforts. Respondents also identified
the relative influence of various factors on the spread of English ivy. The final
three questions pertained to the effectiveness, cost-effectiveness, and political
feasibility of policy alternatives.
Data Collection
A total of 69 individuals completed the survey in February and March of
2013. Survey participants included state and county weed board program
directors and natural resource professionals at state, county, and city levels in both
government and nonprofit sectors. In order to reduce redundancy and balance
spatial representation, typically only one person from each organization,
department, or government program answered the survey. The cities and counties
represented in the survey are all within the Puget Sound region. Only cities with
large metropolitan areas (populations greater than 40,000) were included based on
the assumption that small jurisdictions may not have extensive invasive species
programs. Surveys were created and managed through the website
SurveyMonkey.com. All responses were anonymous.

37

The survey contained eight questions. Employment sector options
included government, nonprofit, private, and other. Geographic management
range choices were state, county, city, or other. For English ivy’s ranking in
management portfolios, respondents chose from top 5, top 10, top 25, or top 50
species or not a priority. Survey designations of the role of volunteers included
very important, important, not important, or not applicable. Factors impacting the
spread of English ivy were characterized as having a strong influence, influence,
or no influence. For the three policy option questions, participants used a Likert
scale to rank a policy’s effectiveness, cost-effectiveness, and political feasibility.
At the end of the survey, there was a place for respondents to contribute brief
comments regarding English ivy policies or the survey design.
Analysis
The main purpose of the analysis was to determine the most appropriate
English ivy policy. Favorable responses (agree and somewhat agree) were
compared to unfavorable responses (disagree or somewhat disagree) using a Chisquare test. The importance of ivy in management portfolios, the role of
volunteers in ivy management, and the influence of various factors on ivy
dispersal were examined by comparing responses according to the participants’
sectors and management ranges.

38

Results
English Ivy Importance, Dispersal Factors, and Volunteer Control Efforts
Preliminary questions addressed English ivy’s ranking in management
portfolios and the role of volunteers in control efforts. A majority of total
respondents and nearly all city-level and nonprofit sector respondents considered
ivy to be at least among their top 10 species (Table 2.1) and claimed volunteers
were important or very important to their English Ivy removal efforts (Table 2.2).
In contrast, most state-level participants did not perceive English ivy as a priority
(Table 2.1) and 58.3% relied on volunteers (n=12) (Table 2).
The next survey question pertained to the relative influence of various
factors on English ivy dispersal. According to respondents, the following factors
most strongly influence dispersal: 1) ivy’s invasive characteristics; 2) a lack of
concerted control efforts and funding; and 3) habitat fragmentation and
disturbance (Table 2.3). A higher proportion of state-level and nonprofit
respondents perceived ivy sales in plant nurseries as having a strong influence
relative to other participant groups (Table 2.3). Few respondents identified
challenges differentiating between invasive and non-invasive ivy cultivars as
strongly influencing dispersal.

39

Table 2.1. Responses from natural resource and weed board professionals in
Washington State regarding the importance of English ivy in their invasive
species management portfolios. “High priority” includes responses indicating
English ivy is within the top 5 or 10 species in a management portfolio whereas
“low priority” refers to respondent selections of top 25 or 50 species or not a
priority.

Management
Range

High Priority
% (N)

Low Priority
% (N)

All Respondents

72.5 (50)

27.5 (19)

State
County
City

41.7 (5)
63.6 (21)
100 (18)

58.3 (7)
36.4 (12)
0 (0)

Government
Non Profit

61.2 (30)
100 (18)

38.8 (19)
0 (0)

Sector

Table 2.2. Responses from natural resource and weed board professionals in
Washington State regarding the importance of volunteers in their English ivy
removal efforts.

Management
Range

All Respondents

Important or
Very Important
%(N)
81.2 (56)

Not Important or
Not Applicable
%(N)
18.8 (13)

State
County
City

58.3 (7)
78.8 (26)
100 (18)

41.7 (5)
21.2 (7)
0 (0)

Government
Non Profit

75.5 (37)
94.4 (17)

24.5 (12)
5.6 (1)

Sector

40

Table 2.3. Responses from natural resource and weed board professionals in
Washington State regarding factors strongly influencing English ivy dispersal.

All
Respondents
Management
Range

Sector

1.
2.
3.
4.
5.

Ivy
Traits1
%
(N)
91.2
(62)

Cultivar
Habitat
Differences2 Disturbance3
%
%
(N)
(N)
3.0
49.3
(2)
(33)

Lack of
Control4
%
(N)
73.1
(49)

Ivy
Sales5
%
(N)
37.3
(25)

State

90.9
(10)

9.1
(1)

54.5
(6)

54.5
(6)

54.5
(6)

County

90.9
(30)

3.1
(1)

50.0
(16)

81.3
(26)

28.1
(9)

City

94.4
(17)

0
(0)

50.0
(9)

66.7
(12)

27.8
(5)

Government

89.6
(43)

2.1
(1)

46.8
(22)

74.5
(35)

27.7
(13)

Non Profit

94.4
(17)

5.6
(1)

50.0
(9)

72.2
(13)

61.1
(11)

English ivy’s invasive characteristics
Difficulty differentiating between invasive and noninvasive cultivars of English ivy
Habitat Fragmentation and Disturbance
Lack of a concerted control effort and funding
English ivy sales in plant nurseries.

English Ivy Policy Preferences
Policy 1: Educate the public and encourage weed boards to control English ivy
locally
The survey responses indicate that the most effective, cost-effective, and
politically feasible English ivy policy is education and localized control (policy 1)
(Figures 2-4.). Based on a Chi-square analysis, policy 1 ranked higher than the
other policies for each of the three criteria (p<0.05) with a few exceptions. A
statewide ban (policy 3) was not significantly different from policy 1 with regard
41

to effectiveness (χ2=1.52, p=0.22) and cost effectiveness (χ2=1.69, p=0.19) nor
was voluntary curtailment of ivy sales (policy 4) different in terms of and political
feasibility (χ2=1.99, p=0.16). The relationship between policy 1 and policy 4 for
cost-effectiveness was on the borderline for statistical significance (χ2=3.74,
p=0.053).
Although policy 1 is somewhat the status quo, participant comments
reveal a desire for an increase in current efforts. Some participants believed
outreach should come from weed boards while others envisioned nursery industry
efforts. One individual identified education as a means to initiate a grassroots
movement among community members to remove ivy in backyards,
neighborhoods, and local parks. Two survey participants remarked that “educate
the public” and “encourage county weed boards to control English ivy locally” are
different policies meriting individual consideration. One of those participants
noted that he/she supports education, but believes weed boards should only
manage species that are not yet widely spread. Another respondent argued that
the state weed board should make English ivy a higher priority.
Policy 2: Impose a tax on the nursery industry to pay for English ivy removal
A majority of respondents indicated that a nursery tax (policy 2) may not
be a realistic policy strategy at this time, in large part due to perceptions of
political feasibility. Although the most common response regarding the political
feasibility of policy 2 was “somewhat disagree”, respondents most often
somewhat agreed with its potential effectiveness and cost-effectiveness (Figures

42

2.2-2.4.). Two respondents commented that a tax would be divisive and unlikely
to garner legislative support. Many participants remarked on the need for more
financial resources for English ivy control but did not necessarily support a tax.
One commenter suggested that utilities contribute to management efforts because
ivy threatens overhead wires.
Policy 3: Implement a statewide ban on English ivy cultivars
The implementation of a statewide English ivy ban (policy 3) invoked
mixed results. As previously mentioned, agreement with the effectiveness and
cost-effectiveness of policy 3 was not statistically different from policy 1. The
most common responses were “agree” for effectiveness and cost-effectiveness but
“somewhat disagree” for political feasibility (Figures 2.2-2.44). One survey
participant hoped the Washington State Department of Agriculture (WSDA)
would add four invasive ivy cultivars to the quarantine list whereas another
person did not envision legislative support for a ban. A third participant noted
that ivy sales from big box stores were only one of many factors contributing to
its spread.
Policy 4: Encourage nurseries to voluntarily curtail the sale of English ivy
Respondents indicated that the voluntary curtailment of English ivy sales
(policy 4) is a favorable policy option. Respondents most often agreed with the
effectiveness and cost-effectiveness of policy 4 (Figures 2.2-2.3). However, the
most common response for political feasibility was “somewhat agree” and the
proportion of favorable responses was significantly lower than for policy 1
43

(χ2=1.99, p<0.16) (Figure 2.4). One respondent noted that the Pacific Northwest
Invasive Plant Council plans to implement a Nursery Certification Program for
retailers curtailing English ivy sales once funding is available.
Policy 5: Do nothing to control English ivy
The option to do nothing to control English ivy (policy 5) was highly
unpopular. The most common response for the effectiveness, cost-effectiveness,
and political feasibility of policy 5 was “disagree” (Figures 2.2.-2.4). Some
survey comments indicated that it is too late for control efforts because English
ivy is widespread and the available seed source is large. One person remarked
that many ivy-infested areas are inaccessible for management (i.e. private
property).

44

EFFECTIVENESS

Policy 1: Education and localized
control
Policy 2: Nursery industry tax
Policy 3: Statewide ivy ban
Policy 4: Voluntary curtailment of
ivy sales
Policy 5: Do nothing
0%

25%

50%

Agree

Somewhat Agree

Neither Agree nor Disagree

Somewhat Disagree

75%

100%

Disagree
Figure 2.2. Responses from natural resource and weed board professionals in
Washington State regarding the effectiveness of policy alternatives for English
ivy management.

45

COST-EFFECTIVENESS
Policy 1: Education and localized
control
Policy 2: Nursery industry tax
Policy 3: Statewide ivy ban
Policy 4: Voluntary curtailment of
ivy sales
Policy 5: Do nothing
0%

25%

50%

Agree

Somewhat Agree

Neither Agree nor Disagree

Somewhat Disagree

75%

100%

Disagree
Figure 2.3. Responses from natural resource and weed board professionals in
Washington State regarding the cost-effectiveness of policy alternatives for
English ivy management.

46

POLITICAL FEASIBILITY

Policy 1: Education and localized
control
Policy 2: Nursery industry tax
Policy 3: Statewide ivy ban
Policy 4: Voluntary curtailment of
ivy sales
Policy 5: Do nothing
0%

25%

50%

Agree

Somewhat Agree

Neither Agree nor Disagree

Somewhat Disagree

75%

100%

Disagree
Figure 2.4. Responses from natural resource and weed board professionals in
Washington State regarding the political feasibility of policy alternatives for
English ivy management.

47

Discussion
Discussion of Results
The overall preference for education and localized control of English ivy
(policy 1) reflects current practices in Washington State. The Washington State
Noxious Weed Control Board (NWCB) maintains a weed list designating plants
as Class A, B, or C depending on their control requirements and distribution
(NWCB 2010b). Class A weeds are new to the area and not widely distributed
(NWCB 2010b). State law requires that public and private landowners extirpate
Class A weeds on their properties (NWCB 2010b). Class B weeds are widespread
in certain areas of the state (NWCB 2010b). The board’s prioritization strategy is
to reduce the abundance of Class B weeds and prevent them from spreading into
new areas (NWCB 2010b). Class C weeds are found throughout Washington, and
the weed board engages the public in education and outreach on the impacts of
those species (NWCB 2010b). County weed boards can opt to require mandatory
control for Class B and C species (NWCB 2010b). In 2002, the Washington State
Noxious Weed Control Board (NWCB) added four English ivy cultivars to the
state noxious weed list as Class C (NWCB 2010a).
There was some opposition to English ivy’s Class C listing during the
NWCB’s public comment period. A few individuals argued ivy should be a
higher priority (Class A or B species) and added to the state’s quarantine list
(English ivy testimony, personal communication, 2002). Others claimed English
ivy’s benefits outweigh environmental costs and more attention should instead be
paid to invaders like Scotch Broom (Cytisus scoparius) and Himalayan blackberry
48

(Rubus armeniacus) (English ivy testimony, personal communication, 2002).
Despite some expressions of concern, the vast majority of letters sent to the
NWCB expressed support for adding English ivy to the noxious weed list.
Although the Class C listing permits localized control and education,
efforts have been relatively limited. No county weed board currently requires
private landowners to remove English ivy. The City of Tacoma did pass a
nuisance ordinance in 2007 prohibiting “unkempt” and “uncultivated” vegetation.
Many cities also conduct their own English ivy maintenance and partner with
nonprofit organizations to coordinate volunteer control efforts. Since English
ivy’s noxious weed listing in 2002, the NWCB has included the plant in its
“Garden Wise” publication, recommending garden alternatives such as crinkleleaf creeper (Rubus pentalobus), kinnikinnik (Arctostaphylos uva-ursi), or
climbing hydrangea (Hydrangea anomala subsp. petiolaris). Survey participants
in this study indicated that localized control and education efforts in western
Washington should increase.
It is not surprising that a tax on the nursery industry (policy 2) was an
unpopular option. A study by Barbier and authors (2013) determined that nursery
industry opposition and uncertainty surrounding invasive species impacts pose
implementation challenges for economic policy instruments. In a survey of
horticultural and weed specialist stakeholders, the authors found that a nursery
industry fee was particularly unpopular. Furthermore, Washington State residents
regularly oppose new taxes. In 2007, Washington voters passed an initiative (I960) requiring a two-thirds majority approval in the legislature for tax or fee
49

increases. The state legislature repealed the decision in 2010 but voters passed
another version in November of that year (I-1053). Even though the state
Supreme Court has since declared unconstitutional subsequent attempts at tax
restrictions (including I-1185), the anti-tax message from voters is clear. The
current political environment in Washington would likely not support policy 2.
Variation among responses regarding a statewide English ivy ban (policy
3) may reflect participant knowledge of policy precedent in other states. Of the
states recently attempting to ban English ivy sales, two failed (Virginia,
Maryland) and one succeeded (Oregon). While not all varieties of English ivy are
invasive, Oregon’s statewide ban applies to all varieties (Scigliano 2012). The
implementation of a Washington state ban of English ivy would require the
Washington State Department of Agriculture (WSDA) to add the species to its
quarantine list (WAC 16-752-600 through 690). The WSDA evaluates the costs
and benefits of any proposed changes to the list as well as impacts to stakeholder
groups. Currently, there are 64 terrestrial plants on Washington’s quarantine list,
all of which are either Class A or Class B noxious weeds (Washington State
Department of Agriculture 2010). Inspectors are already overwhelmed: there are
only eleven WSDA employees in charge of inspecting 6,500 licensed nurseries
for quarantined plants as well as all timber and hay exports for insects (T.
Wessels, personal communication, May 17, 2013). A statewide ban of English
ivy sales would not impact horticultural imports from Canada (Tom Wessels,
personal communication, 2013). Without a comprehensive risk assessment, the
World Trade Organization (WTO) views international quarantine as arbitrary
50

barriers to trade (Powell, 2004). Limited resources and the complicated political
nature of statewide bans pose potential barriers to policy 3.
General agreement among respondents in favor of voluntary measures
(policy 4) reflects actions occurring to a certain extent in Washington State and
elsewhere. In 2006, the Washington State Nursery and Landscape Association
(WSNLA) endorsed a “voluntary code of conduct” to reduce invasive species
introductions and educate the public on the impacts of invasions (Center for Plant
Conservation 2013). Since then, the WSNLA has included information on
invasive species in its trade magazine and collaborated with the NWCB on
educational materials (Center for Plant Conservation 2013). The Washington
State Native Plant Society’s “IvyO.U.T” website has its own list of ten nurseries
in Washington pledging to curtail English ivy sales (Washington Native Plant
Society 2012). Touza and authors (2007) assert that the success of voluntary
codes of conduct depends on the extent of their promotion among industry
professionals and the public. With greater promotion of current efforts, policy 4
may be a viable option but perhaps less effective than policy 1.
The vast majority of respondents rejected the “do nothing” option (policy
5); similarly, most studies acknowledge that invasive species require
management. The few academics opposing management argue that human
introduction of native organisms is natural because humans are part of nature.
Lodge and Shrader-Frechette (2003) claim that assuming everything humans do is
“natural” and therefore “good” is a “naturalistic fallacy” and undermines the basis
of civil society. Management opponents also decry reports of economic and
51

ecological impacts as exaggerated. Some academics believe scientists should not
subjectively determine whether a species is “good” or “bad” (Lodge and ShraderFrechette, 2003). The counter argument would be that science can never truly be
objective and the pressing-nature of biological invasions merits a decisive
response from the scientific community. Stakeholders and the academic
community overwhelmingly object to policy 5.
Discussion of Methods
One of the strengths of this study was the high response rate. According
to Muňoz-Leiva and authors (2010), typical response rates for electronic surveys
in the early years of email were approximately 50%, and they have continued
dropping ever since. However, personalized phone calls and emails to
participants prior to the survey may account for the high response rate in this
study (92%).
This study also has some limitations. First, the policy alternatives are
general and not exhaustive. The survey did not specify the details of each policy
(i.e. the rate at which a nursery would be taxed) nor did it elaborate on the
logistics of implementation and enforcement. Other policies that merit future
consideration include the implementation of environmental bonds, tariffs and
graduated license fees; the conservation of large tracts of habitat; and the
requirement of English ivy removal on private and public property. The purpose
of a general approach is to assess which types of policies are most favorable so

52

that a follow-up study can address particular components of the top one or two
policies.
Second, weed board and natural resource professionals are only one type
of stakeholder involved in invasive species issues. Nursery industry professionals
and the gardening public also have a stake in English ivy dispersal. Surveys to
weed specialists are intended as a preliminary step in policymaking, and other
stakeholders should participate in the decision-making process as well. Although
initial studies can focus on expert opinions, wide-ranging stakeholder buy-in
further along in the process is often helpful for successful policy implementation.
Third, survey questions relied on assumptions about the survey
participant’s prior knowledge. The choice of assessment criteria assumed
respondents had a familiarity with the costs and effectiveness of each policy
alternative as well as Washington’s political climate. Political scientists coined
the term “bounded rationality” to describe how the decisions of experts are
confined by limited information, resources, and human cognition (Clark 2002,
Fiorino 1995). Limits to expert knowledge may have constrained survey
responses and the subsequent formation of generalized conclusions about English
ivy polices.
Fourth, there are drawbacks to survey methodology. Weed specialists
tend to work in the field most days and may not regularly check email. Also, the
target respondent universe is more difficult to control for an anonymous webbased survey. For example, one respondent forwarded the survey on to a few

53

other people, which may have confounded the target survey universe slightly. In
addition, there may have been some variation in the respondents’ interpretation of
different agreement levels. Despite some logistical shortcomings, the electronic
survey method is an efficient and inexpensive means of gathering expert opinion.
Future Work
Various modifications or additions to this study could contribute to
knowledge about survey methodology and English ivy policy alternatives. The
next step in pursuing the most appropriate statewide efforts could be to conduct a
focus group or follow-up survey regarding cost and implementation strategies
specific to the most favorable policy option(s) (i.e. policies 1, 3, and/or 4). In
addition, policymakers should set target outcomes (i.e. acreage of restored
habitat) and evaluate the effectiveness and cost-effectiveness of the chosen policy
strategy once enacted. Economic analyses of policies should include ecosystem
services. The input of other stakeholders in the decision-making process can
anticipate potential political feasibility problems and encourage buy-in. Followup studies, broad economic analyses, and increased stakeholder involvement
could all add to this study’s conclusions.
Conclusion
Analysis is warranted for invasive species policies because management
typically contributes to the greater public good. Expert opinion surveys can serve
as a cost-effective and user-friendly solution to the lack of quantitative data for a
particular invader in the evaluation of policy alternatives. Weed board and
54

natural resource professionals in participating in this study most often favored the
policy alternative regarding education and localized control efforts (policy 1) with
regard to effectiveness, cost-effectiveness, and political feasibility. The second
most highly favored policy option was voluntary curtailment of English ivy sales
in nurseries (policy 4). Although results for cost-effectiveness and political
feasibility were similar between policies 1 and 4, the proportion of favorable
responses for the effectiveness of policy 4 was significantly lower than for policy
1 (χ2=13.48, p<0.001). Future research could utilize focus groups or follow-up
surveys to explore the rationale for policy preferences as well as establish
implementation details for the most favorable policy.

55

Appendices
Table 2.4. Responses from natural resource and weed board professionals
regarding the effectiveness of statewide policy alternatives in limiting the spread
of English ivy in Washington State.
Agree or
Somewhat Agree
% (N)

Disagree or
Somewhat
Disagree
% (N)

Educate the public and encourage
county weed boards to control English
Ivy locally

71.7 (43)

2.9 (2)

Impose a tax on the nursery industry to
pay for English Ivy removal

55.1 (38)

26.1 (18)

Implement a statewide ban on the sale
of English Ivy cultivars

82.6 (57)

5.8 (4)

Encourage nurseries to voluntarily
curtail the sale of English Ivy

66.7 (46)

23.2 (16)

Do nothing to control English Ivy

0 (0)

98.5 (66)

56

Table 2.5. Responses from natural resource and weed board professionals
regarding the cost-effectiveness of statewide policy alternatives in limiting the
spread of English ivy in Washington State.
Agree or
Somewhat Agree
% (N)

Disagree or
Somewhat
Disagree
% (N)

Educate the public and encourage
county weed boards to control English
Ivy locally

88.4 (61)

5.8 (4)

Impose a tax on the nursery industry to
pay for English Ivy removal

55.1 (38)

29.0 (20)

Implement a statewide ban on the sale
of English Ivy cultivars

78.3 (54)

1.3 (9)

Encourage nurseries to voluntarily
curtail the sale of English Ivy

69.6 (48)

14.5 (10)

Do nothing to control English Ivy

1.5 (1)

94.1 (64)

57

Table 2.6. Responses from natural resource and weed board professionals
regarding the political feasibility of statewide policy alternatives in limiting the
spread of English ivy in Washington State.
Agree or
Somewhat Agree
% (N)

Disagree or
Somewhat
Disagree
% (N)

Educate the public and encourage
county weed boards to control English
Ivy locally

82.6 (57)

5.8 (4)

Impose a tax on the nursery industry to
pay for English Ivy removal

7.2 (5)

66.7 (46)

Implement a statewide ban on the sale
of English Ivy cultivars

24.6 (17)

50.7 (35)

Encourage nurseries to voluntarily
curtail the sale of English Ivy

68.1 (47)

11.6 (8)

Do nothing to control English Ivy

42.0 (29)

37.7 (26)

58

59

Figure 2.8 Ordination comparing survey responses of natural resource and weed
board professionals regarding English ivy’s relative importance in management
porftolios (top 5, top 10, top 25, top 50, or not a priority) according to geographic
management range (state=1, county=2, city=3, other=4) (A=0167, p<0.001).

60

Survey Questions

61

62

63

64

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Station, Fire Sciences Laboratory (Producer). Retrieved from
http://www.fs.fed.us/database/feis/plants/vine/hedhel/all.html
Washington State Department of Agriculture (2011). English ivy – four cultivars
only, “Hedera helix ‘Baltica’, ‘Pittsburgh’, and ‘Star’; H. Hibernica
‘Hibernica’”: distribution 2011. Retrieved from
http://www.nwcb.wa.gov/siteFiles/English%20Ivy%202011.pdf
Washington State Noxious Weed Control Board (2001). Draft written findings of
the Washington State Noxious Weed Control Board (English ivy).
Retrieved from http://www.nwcb.wa.gov/siteFiles/Hedera.pdf.
Wilcove, D. S., Rothstein, D., Dubow, J., Phillips, A., & Losos, E. (1998).
Threats to imperiled species in the United States. BioScience, 48(8), 607615.

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3. Research Significance and Future Directions
Research Significance
My thesis explored invasive species policy analysis from an
interdisciplinary perspective. Chapter One reviewed the academic literature
pertaining to major themes in invasive species research. With regard to invasion
ecology, researchers have examined the characteristics intrinsic to invasive
species and invaded habitats. A number of studies have identified the
anthropogenic drivers of invasive species dispersal, including horticulture.
Researchers have developed bioeconomic models to calculate the costs associated
with particular invaders and have analyzed the ability of economic instruments to
limit future invasions. Studies on risk assessments have incorporated various
factors in the evaluation of invasion risk for a given species or pathway.
Restoration biology research has investigated the efficacy of various prevention,
eradication, and control strategies. In response to a growing concern regarding
the ecological and economic impacts of invasive species, governments and
nongovernmental organizations have collaborated on policies to manage invaders
at the international, federal, state, and local levels.
Chapter Two presented the results of my investigation of expert opinion
survey utility in identifying favorable and realistic policies for an invasive plant
species. Web-based surveys are an inexpensive and efficient means of gathering
data on the management priorities and policy preferences of expert stakeholders,
despite the unlikelihood of including all policy alternatives and reaching every
stakeholder. I surveyed natural resource and weed board professionals to
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determine the most effective, cost-effective, and politically-feasible management
strategy for English ivy, an invasive plant in Washington State. My survey results
indicated that respondents perceive English ivy as a priority species in the Puget
Sound region and prefer education and localized management as a policy
approach. Although the policy preference reflects current practices in
Washington State, participant comments revealed a desire for enhanced efforts.
Future Directions for Invasive Species Research and Management
As demonstrated in Chapter One of this thesis, diverse disciplines, such as
invasion ecology, restoration ecology, population biology, geography, economics,
political science, and philosophy, all address invasive species issues in some way.
Chornesky and Randall (2003) suggest that greater interdisciplinary collaboration
would contribute to better understanding and management of invasive species. It
is also necessary that individual researchers have some foundation of knowledge
in areas outside their primary disciplines. For example, it would be helpful for
scientists to understand the political process in order to guide the formulation of
research questions that are relevant to policymaking and management.
Chornesky and Randall (2003) also recommend future research focused on
the potential impact of global climate change on the invasion process. Changes in
temperature and precipitation will likely alter the distribution of both native and
invasive species. Invaders tend to be highly adaptive and may gain an even
further competitive advantage in the advent of climate change (Chornesky &
Randall 2003). As an invasive species in both Oregon and California, English ivy
would likely continue invading habitats in Washington if temperatures increased.

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English ivy has demonstrated phenotypic plasticity which contributes to its
overall ability to adapt to environmental change. Research on English ivy’s likely
response to climate change would help inform future statewide management
policies.
Future studies should explore policy analysis options. My thesis addresses
general policy alternatives for a specific invader. A follow-up survey or a focus
group could identify implementation details and elucidate the reasons behind
stakeholder preferences. Follow-up questions for the English ivy survey
participants could focus on specific information regarding the preference for
education and localized control efforts including the content of educational
materials, target management goals, stakeholder responsibility for administering
education and leading control efforts, and funding sources. Understanding the
reasons why respondents opposed certain policies would also be beneficial. The
English ivy survey respondents did not perceive a statewide ban as a politically
feasible policy option even though Oregon recently implemented one. A followup study could identify whether respondents are aware of the Oregon ban, if they
view Oregon’s ban as ineffective, or if they believe the Washington political
environment is different.
Species-specific economic studies would also enhance the policy analysis
process. Research on a particular invader’s impact on ecosystem services would
help define the policy problem and inform the selection of policy alternatives.
English ivy impacts tree survival and germination which in turn reduces arboreal
ecosystem services. Future studies could investigate English ivy’s influence on

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other ecosystem services, such as erosion control and water infiltration. English
ivy’s public health impact as a common habitat for rats is another important
consideration. Research on the economic importance of English ivy to the
nursery industry and the viability alternative groundcover plants would indicate if
voluntary curtailment of ivy sales among nurseries is a reasonable expectation.
Lastly, incorporating expert opinion surveys into policy analyses can
substitute for the lack of quantitative data on a number of plant and animal
invaders. The flexibility and efficiency of web-based survey methodology could
make data collection on any type of invasive species virtually instantaneous at
very little cost. The formulation of an invasive species survey template and
database could inform policies at the local, regional, or even global level.

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Literature Cited
Barbier, E. B., Knowler, D., Gwatipetza, J., Reichard, S. H., & Ransom-Hodges,
A. (2013). Implementing policies to control invasive plant species.
BioScience, 63:2, pp. 132-138.
Chornesky, E. A. & Randall, J. M. (2003). The threat of invasive alien species to
biological diversity: setting a future course. Annals of the Missouri
Botanical Garden, 90:1, pp. 67-76.
Eiswerth, M. E. & van Kooten, G. C. (2002). Uncertainty, economics, and the
spread of invasive species. American Journal of Agricultural Economics,
84, pp. 1317-1322.

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Item sets

The Evergreen State College Masters Theses: Environmental Studies

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Baur_A-MESthesis2013.pdf