Definition Clarification and Guidance White Paper
fom the National Invasive Species Advisory Committee
By Robert E. Schutzki
Professor, Department of Horticulture
Michigan State University
* Used with permission of Dr. Schutzki and MNLA
In April 2006, the Invasive Species Advisory Committee (ISAC) submitted a document titled
‘Invasive Species Definition Clarification and Guidance White Paper’ to the National Invasive
Species Council (NISC) for adoption. A white paper is basically a term that describes a report.
It is a detailed discussion that defines the subject, presents its background, and addresses the
purpose or intent for the white paper. Before we get into the white paper itself, let’s review the
NISC and ISAC.
The National Invasive Species Council was established through Executive Order 13112. It is an
inter-Departmental council that helps to coordinate and endure complementary, cost-efficient,
and effective Federal activities regarding invasive species.
The Council is composed of 13 Federal Departments and Agencies. Departments represented
include; Agriculture, Commerce, Interior, State, Defense, Homeland Security, Treasury,
Transportation, Health and Human Services, Environmental Protection Agency, the U.S. Agency
for International Development, the U.S. Trade Representative, and the National Aeronautics and
Space Administration. The Council is responsible for the development and execution of the
National Invasive Species Management Plan (NISMP) which was released in 2001. The NISMP
and progress reports on activities related to the plan can be obtained by visiting
The Executive Order also established the Invasive Species Advisory Committee to advise the
federal government on invasive species issues and to act as stakeholder representatives. The
Committee is composed of approximately thirty stakeholders from state organizations, industry,
conservation groups, scientists, academia, and other interests. In their capacity to advise and aid
in addressing the issues associated with administering the management plan, the “Invasive
Species Definition Clarification and Guidance White Paper’ was prepared and submitted to the
The purpose of the “Invasive Species Definition Clarification and Guidance White Paper” is to
provide a non-regulatory policy interpretation of the term invasive species by identifying what is
meant, and just as important, what is not meant by the term.” Executive Order 13112 defines an
invasive species as “an alien species whose introduction does or is likely to cause economic or
environmental harm or harm to human health.” A more detailed definition within the National
Invasive Species Management Plan (NISMP) states that an invasive species is “a species that is
non-native to the ecosystem under consideration and whose introduction causes or is likely to
cause economic or environmental harm or harm to human health.” The Executive Order also has
a provision for excusing a plant’s invasiveness when its benefits clearly outweigh the potential
harm. Under Federal agency duties, it states that it “shall to the extent practicable and permitted
by law, not authorize, fund, or carry out actions that it believes are likely to cause or promote the
introduction or spread of invasive species in the United States or elsewhere unless pursuant to
guidelines that it has prescribed, the agency has determined and made public its determination
that the benefits of such actions clearly outweigh the potential harm caused by invasive species;
and that all feasible and prudent measures to minimize risk of harm will be taken in conjunction
with the actions.” The intent of this provision is carried into the NISMP where it states that
focus will be “on non-native organisms known to cause or likely to cause negative impacts and
that do not provide an equivalent or greater benefit to society.” The ISAC white paper further
states that “some non-native species are considered harmful, and therefore, invasive by some
sectors of our society, while others consider them beneficial. This discontinuity is reflective of
the different value systems operating in our free society, and contributes to the complexity of
defining the term invasive species. While there have been numerous attempts to clarity the term
invasive species, there continues to be uncertainty concerning the use and perceived meaning of
the term, and consequently over the prospective scope of actions proposed in the NISMP.
Options related to private property use, pet ownership, agriculture, horticulture, and aquaculture
enterprises may be affected depending upon the definition, use, and policy implications of the
term invasive species. ISAC recognizes that biological and ecological definitions will not
precisely apply to regulatory definitions. We believe, however, that our clarification will apply
to all taxa of invasive species in all habitats and furthermore, our explanation will be functional
and acceptable to most stakeholders. ISAC simply wants to clarify what is meant and what is not
meant by the term invasive species in the technical sense and to provide insight into those areas
where societal judgments will be necessary to implement effective public policy. The utility of
our clarification should be in education, conflict resolution, and efficiency in the planning,
prevention, control/eradication, and management of invasive species.”
The White Paper discusses invasive species as it applies to the perception of harm and actual
environmental harm, as it relates to all of the concepts and conditions involved with identifying a
plant as a weed, and as a function of biogeography. It also provides examples to support their
interpretation and clarification of what they do mean and what they do not mean with respect to
invasive species. The following excerpts from the White Paper are intended to keep you
informed and possibly make you more aware of the issue as it is seen at the national level. The
complete White Paper can be obtained by visiting <<http://www.invasivespeciesinfo.gov>>. At
the website, go to the Council pages and click on the Invasive Species Advisory Council.
The following information is excerpted from the “Invasive Species Definition Clarification and Guidance White
Perception to Cause Harm
Complications concerning the concept of invasive species arise from differing human values and
perspectives. Differing perceptions of the relative harm caused or benefits gained by a particular
organism are influenced by different values and management goals. If invasive species did not
cause harm, we would not be nearly as concerned. Perceptions of relative benefits and harm also
may change as new knowledge is acquired, or as human values or management goals change.
For a non-native organism to be considered an invasive species in the policy context, the negative
effects that the organism causes or is likely to cause are deemed to outweigh any beneficial
effects. Many non-native introductions provide benefits to society and even among species that
technically meet the definition of invasive, societal benefits may greatly exceed any negative
effects (for example crops and livestock raised for food). However, in some cases any positive
effects are clearly overshadowed by negative effects, and this is the concept of causing harm.
Such organisms constitute a small fraction of non-native species, but as a consequence of their
ability to spread and establish populations outside of their native ranges, they can be disastrous
for the natural environment, the economies it supports, and/or public health. Because invasive
species management is difficult and often very expensive, these worst offenders are the most
obvious and best targets for policy attention and management.
It is also essential to recognize that invasive species are not those under human control or
domestication; that is, invasive species are not those that humans depend upon for economic
security, maintaining a desirable quality of life, or survival. However, the essential test is that
populations of these species must be under control. Escaped or feral populations of formerly
domesticated plants and animals would be considered invasive species if all of the concepts and
conditions are met as outlined in “Weeds As Examples”.
Weeds As Examples
Weeds provide good examples to clarify what is meant by an invasive species because most
people have a concept of what constitutes a “weed”.
Invasion can be thought of as a process that, in our example, a plant must go through to become a
successful, yet harmful invader. Several barriers must be overcome for a plant to be considered
an invasive weed. Invasive weeds are invasive species.
Large-scale geographical barriers
First, a geographical barrier must be overcome. Examples include a mountain range, ocean, or
similar physical barrier to movement of seeds and other reproductive plant parts. Plants that
overcome geographical barriers are known as alien plants or alien species. Alien plants are
non-native species. Therefore, non-native plants are those that occur outside of their natural
range boundaries, and this most often is mediated by humans either deliberately or
The second set of obstacles that a non-native plant must overcome is barriers to germination and
survival in its new location. These typically are environmental barriers such as adequate
moisture availability to allow successful germination and survival of seedlings that will continue
to grow to maturity. Other physical barriers might be soil pH, nutrient availability, or
competition for resources from neighboring plants.
The third obstacle that a non-native plant must overcome to be considered an invasive weed is to
form a population that is self-sustaining and does not need re-introduction to maintain to survive
and thrive in its new environment. Once this occurs, this population of non-native plants is
considered to be established. Environmental barriers to survival and establishment are similar.
Dispersal and spread barriers
Established non-native plants must overcome barriers to dispersal and spread from their site of
establishment to be considered invasive plants. Additionally, the rate of spread must be
relatively fast. However, this movement or spread alone does not necessarily make this non-
native plant an invasive weed or invasive species.
Harm and impact
Finally, a plant is deemed to be invasive if it causes negative environmental, economic, or human
health effects, which outweigh any beneficial effects. For example, yellow starthistle is a source
of nectar for bee producers. But the displacement of native and other desirable plant species
caused by yellow starthistle leads to dramatically decreased forage for wildlife and livestock,
which severely disrupts the profitability of associated businesses. These negative effects greatly
overshadow the positive effects and thus, define harm caused by yellow starthistle and explain
why it is considered an invasive species.
A Biogeographical Context
An invasive species may be invasive in one part of the country, but not in another. A
biogeographical context must be included when assessing whether a non-native species should be
considered an invasive species. Lake trout are highly desirable in the Great Lakes where they are
native, but are considered an invasive species in Yellowstone Lake. They compete with native
cutthroat trout for habitat, which decrease their populations. Kentucky bluegrass would be
considered an invasive species in Rocky Mountain National Park in Colorado, but considered
non-invasive a mere 60 miles away at a golf course in Denver. English ivy is considered a good
ground cover species in the Great Plains and Midwest, but is a highly invasive weed in the
forests of the Pacific Northwest and Eastern U.S. where it out competes native plants and
displaces the associated animal communities.
The “Gray” Area
There are obvious examples of invasive species such as snakehead fish, yellow starthistle, or
Phytophthora ramorum (the organism that causes sudden oak death); and there are obvious
examples of species that are not invasive, namely native plants and animals. There are, however,
non-native organisms for which it will be difficult to make a determination and these should be
subject to assessment. Whether these non-native organisms will be considered invasive species
will depend upon human values. For example, European honeybees are cultured to produce
honey and pollination services, and even though they form wild populations in many parts of the
country and occasionally create problems by building hives in the walls of homes or can be a
human health problem for individuals that are highly allergic to their sting, most would not
consider them an invasive species because they produce a desired food product.
Chinese and Oriental clematis serves as another gray area example. Chinese clematis (virgin’s
bower, orange peel) is a popular ornamental that has been planted worldwide. However, it has
escaped cultivation in several western states where its populations can spread, particularly in
shrubland, on riverbanks, sand depressions, along roadsides, in gullies, and along riparian forests
in hot dry valleys, deserts, and semi-desert areas. Escaped populations of Chinese clematis occur
in Idaho, Nevada, Utah, New Mexico, and Colorado. So far, it is considered an invasive species
only in Colorado where it has spread dramatically from its site of introduction and displaced
native plant species.
We use environmental harm to mean biologically significant decreases in native species
populations, alterations to plant and animal communities or to ecological processes that native
species and other desirable plants and animals and humans depend on for survival.
Environmental harm may be a result of direct effects of invasive species, leading to biologically
significant decreases in native species populations. Examples of direct effects on native species
include preying and feeding on them, causing or vectoring diseases, preventing them from
reproducing or killing their young, out-competing them for food, nutrients, light, nest sites or
other vital resources, or hybridizing with them so frequently that within a few generations, few of
any truly native individuals remain. Environmental harm also can be the result of an indirect
effect of invasive species, such as the decreases in native waterfowl populations that may result
when an invasive wetland plant decreases the abundance of native plants and thus, decreases
seeds and other food that they provide and that the waterfowl depend upon. Environmental harm
also includes significant changes in ecological processes, sometimes across entire regions, which
result in conditions that native species and even entire plant and animal communities cannot
tolerate. For example, some non-native plants can change the frequency and intensity of
wildfires, or alter the hydrology of rivers, streams, lakes and wetlands and that is why they are
considered invasive species. Others can significantly alter erosion rates, for example, trapping
far more wind-blown sand than native dune species, or holding far less soil than native grassland
species following rainstorms. Some invasive plants and microorganisms can alter soil chemistry
across large areas, significantly altering soil pH or soil nutrient availability. Environmental harm
also includes significant changes in the composition and even the structure of native plant and
animal communities. Environmental harm may also cause or be associated with economic losses
and damage to human, plant and animal health.
Additional Examples of Impacts Caused by Invasive Species
Specific examples of the harm caused by invasive species are useful to further clarify the
definition. The following list of examples is not meant to be comprehensive, but offers further
Impacts to Human Health
Poisonous plants: Exposure to the sap of Tree-of-heaven/Chinese sumac tree has caused
inflammation of the heart muscle (myocarditis) in workers charged to clear infested areas.
Afflicted personnel experienced fever/chills, chest pain that radiated down both arms, and
shortness or breath. Exposure occurred when sap from tree-of-heaven contacted broken skin.
Such exposure has caused hospitalization, medical expense, and lost productivity due to absence
from work (Bisognano et al. 2005).
Impacts to Natural Resources
Decreased carrying capacity for wildlife and livestock: Expansion of leafy spurge, yellow
starthistle, or other unpalatable invasive weeds displace desirable forage plants and may allow
fewer grazing animals to survive in infested areas (DiTomaso 2001; Lym and Messersmith 1985;
Lym and Kirby 1987).
Impacts to Recreational Opportunities and Other Human Values
Emerald ash borers were first detected in the U.S. in 2002. They currently are found in
Michigan, Ohio, and Indiana. Emerald ash borer larvae tunnel under bark of ash trees and could
eliminate ash as a street, shade, and forest tree throughout the U.S. Estimated replacement cost
in six Michigan counties is $11 billion and an additional $2 million in lost nursery sales
(Chornesky et al. 2005).
Altered business opportunities
The concern over Sudden Oak Death Syndrome caused by the pathogen Phytophthora ramorum
is causing drastic changes in available nursery stock by nurseries and landscape businesses. This
clearly impacts the profitability of these businesses and choice by consumers and could devastate
oak forests nationwide (Chornesky et al. 2005; Rizzo and Garbelotto 2003).
Altered ecosystems and recreational opportunities
The submersed aquatic plant hydrilla forms dense canopies at the water surface that raise surface
water temperatures, change pH, exclude light, and consume oxygen, resulting in native plant
displacement and stunted sport fish populations. This example of an altered aquatic ecosystem
caused by an invasive aquatic weed also negatively affects recreation and businesses that depend
upon that human activity (Colle et al. 1987).
Invasive species are those that are not native to the ecosystem under consideration and that cause
or are likely to cause economic or environmental harm or harm to human, animal, or plant health.
Plant and animal species under domestication or cultivation and under human control are not
invasive species. Furthermore, for policy purposes, to be considered invasive, the negative
impacts caused by a non-native species will be deemed to outweigh the beneficial effects it
provides. Finally, a non-native species might be considered invasive in one region, but not in
another. Whether or not a species is considered an invasive species depends largely on human
values. By attempting to manage invasive species, we are affirming our economic and
environmental values. Those non-native species judged to cause overall economic or
environmental harm or harm to human health may be considered invasive, even if they yield
some beneficial effects. Society struggles to determine the appropriate course of action in such
cases, but in a democratic society that struggle is essential.
Many invasive species are examples of “the tragedy of the commons”, or how actions that benefit
one individual’s use of resources may negatively impact others and result in a significant overall
increase in damage to the economy, the environment, or public health. In ISAC’s review of
Executive Order 13112, the public domain is specifically represented; however, the
implementation of the NISMP has prompted concerns over the rights of personal and private
property owners. Property rights are of great importance in the U.S. and one outcome of the
NISMP should be to recognize the right to self determination by property owners and promote
collaboration on invasive species management. The right to self determination is an important
concept in a democratic society, however, with that right comes personal responsibility and
stewardship, which includes being environmentally responsible. The natural environment that
our society enjoys, recreates in, and depends upon to support commerce must be conserved and
maintained. Effective invasive species management is just one aspect of conserving and
maintaining our nation’s’s natural environment, the economies it supports, and the high quality
of life that our society enjoys.
In conclusion, the invasive plant issue is extremely complex and crosses many discipline and
commodity boundaries. Problems have arisen with individual interpretation of the intent of the
Executive Order when addressing concerns over the classification, use, and impact of invasive
plants and the subsequent action that should be taken. The ISAC White Paper provides another
resource to aid in our understanding and help shape the way we address the issue. It reinforces
key concerns about identifying and documenting environmental harm, assessing benefits when
determining action on a given species, and considering regional differences in behavior when
determining whether a plant should be classified as invasive. “Weed As Examples” provides
additional criteria to aid in determining invasiveness. As expressed in the White Paper, several
barriers must be overcome for a plant to be considered an invasive weed. Escaped or feral
populations of formerly domesticated plant and animals would be considered invasive species if
the concepts and conditions of large-scale geographical barriers, survival barriers, establishment
barriers, dispersal and spread barriers, and harm and impact are met.
The information presented and discussed provides useful insight into identifying: how we as an
industry can have a positive impact on minimizing the impact of harmful invasive plants; how
we as an industry can address the issue both within and outside of our boundaries; and equally
important, what we as an industry should expect as a set of standards in dealing with the issue
from broad-based collaboration with those outside of our industry. As members of the green
industry, we have an invested interest in our natural and built environments. We contribute to
the quality of life as work, home, and play. It is important for us to get involved and be part of
On a final note, Amy Frankmann, MNLA’s Executive Director, has been recently named to the
ISAC. We would like to congratulate Amy on her appointment and extend our appreciation for
her willingness and commitment to represent the green industry on this critical and complex
References from the White Paper cited in this article:
Bisognano, J.D., K.S. McGrody, and A.M. Spence. 2005. Myocarditis from the Chinese sumac
tree. Annals Internal Medicine 143(2):159.
Chorensky, E.A., A.M. Bartuska, G.H. Aplet, K.O. Britton, J. Cummings-Carlson, F.W. Davis, J.
Eskow, D.R. Gordon, K.W. Gottschalk, R.A. Haack, A.J. Hansen, R.N. Mack, R.J. Rahel, M.A.
Shannon, L.A. Wainger, and T.B. Wigley. 2005. Science priorities for reducing the threat of
invasive species to sustainable forestry. BioSci. 55(4):335-348.
Colle, D.E., J.V. Shireman, W.T. Haller, J.C. Joyce, and D.E. Canfield. 1987. Influence of
Hydrilla on Harvestable Sport-Fish Populations, Angler Use, and Angler Expenditures at Orange
Lake, Florida. North American Journal of Fisheries Management 7:410-417.
DiTomaso, J. 2001. Element stewardship abstract: Centaurea solstitialis L. Weeds on the web:
The Nature Conservancy wildland invasive species program. [Online]
Lym, R.G. and C.G. Messersmith. 1985. Cost effectiveness of leafy spurge control during a
five-year management program. North Dakota Farm Res. 43(1):7-10.
Lym, R.G. and D.R. Kirby. 1987. Cattle foraging behavior in leafy spurge infested rangeland.
Weed Technol. 1:314-318.
Rizzo, D.M. and M. Garbelotto. 2003. Sudden oak death: Endangering California and Oregon
forest ecosystems. Frontiers in Ecology and the Environment 1:197-204.
* Originally published in The Michigan Landscape (January 2007, Vol. 50, No.1). Used with
permission of MNLA and Dr. Robert E. Schutzki.