Invasive Species Definition Clarification and Guidance White Paper

Submitted by the Definitions Subcommittee of the

Invasive Species Advisory Committee (ISAC)

Approved by ISAC April 27, 2006

Preamble:

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." In the Executive Summary of the National Invasive Species Management Plan (NISMP) the term invasive species is further clarified and defined as "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." To provide guidance for the development and implementation of the NISMP, the National Invasive Species Council (NISC) and the Invasive Species Advisory Committee (ISAC) adopted a set of principles outlined in Appendix 6 of the NISMP. Guiding Principle #1 provides additional context for defining the term invasive species and states "many alien species are non-invasive and support human livelihoods or a preferred quality of life." However, some alien species (non-native will be used in this white paper because it is more descriptive than alien), for example West Nile virus, are considered invasive and undesirable by virtually everyone. Other non-native species are not as easily characterized. For example, 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.

NISC is engaged in evaluating and updating the 2001 NISMP and is developing comments for a revised action plan as required by the EO 13112. While there have been numerous attempts to clarify 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.

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, which often occurs as 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 plants and alien species are non-native species. Therefore, non-native plants are those that occur outside their natural range boundaries, and this most often is mediated by humans either deliberately or unintentionally.

Survival barriers

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.

In particular, the desire to consider a non-native species as ‘invasive’ may trigger a risk/benefit assessment process to determine whether regulatory action is warranted. All these uncertainties have stood and could continue to stand in the way of progress in actions and policy development to prevent new invasions and manage existing invasive species. While it is not the purpose of this white paper to define a risk/benefit assessment process, development of such a process must be open and efficient to minimize the uncertainties.

This white paper is intended to provide a non-regulatory policy interpretation of the term

The utility of our clarification should be in education, conflict resolution, and efficiency in the planning, prevention, control/eradication, and management of

2 invasive species by identifying what is meant, and just as important, what is not meant by the term. 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. invasive species.

Weeds As Examples

(continued)

Establishment barriers

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 a population base such that it continues 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. posted by Carla 

Invasive Species Definition Clarification and Guidance White Paper