Invasive Plant Pests Definitions and Criteria

The following is a list of key published definitions of invasive and criteria to determine invasiveness.

These are compiled from various sources including 1) exotic species list, ranking and assessment methods, and management guidelines 2) policy or law, and 3) other published literature.

I. Invasive Exotic Species List

A List of Florida's Most Invasive Species (1999) Florida Exotic Pest Plant Council

Definitions: Exotic–a non-indigenous species, or one introduced to this state, either purposefully or accidentally. A naturalized exotic, such as those listed here, has escaped into the wild where it reproduces on its own either sexually or asexually. Native–a species already occurring in Florida at the time of European contact (1500). Invasive– a variable condition defined by the category to which the species is assigned.

Abbreviations used

Category I–Species that are invading and disrupting native plant communities in Florida. This definition does not rely on the economic severity or geographic range of the problem, but on the documented ecological damage caused.

Category II—Species that have shown a potential to disrupt native plant communities. These species may become ranked as Category I, but have not yet demonstrated disruption of natural Florida communities.

B. CalEPPC Pest Plants of Greatest Ecological Concern (Oct. 1999) California Exotic Pest Plant Council

The CalEPPC list is based on information submitted by our members and by land managers, botanists and researchers throughout the state, and on published sources. The list highlights non-native plants that are serious problems in wildlands (natural areas that support native ecosystems, including national, state and local parks, ecological reserves, wildlife areas, national forests, BLM lands, etc.).

List categories include:

List A: Most Invasive Wildland Pest Plants; documented as aggressive invaders that displace natives and disrupt natural habitats. Includes two sub-lists:

List A-1: Widespread pests that are invasive in more than 3 Jepson regions (see bottom of List A page)

List A-2: Regional pests invasive in 3 or fewer Jepson regions.

List B: Wildland Pest Plants of Lesser Invasiveness; invasive pest plants that spread less rapidly and cause a lesser degree of habitat disruption; may be wide-spread or regional. Pest plants with potential to spread explosively; infestations currently small or localized. If found, alert CalEPPC, County Agricultural Commissioner or California Department of Food and Agriculture.

Need More Information: Plants for which current information does not adequately describe nature of threat to wildlands, distribution or invasiveness. Further information is requested from knowledgeable observers.

Annual Grasses: New in this edition; a preliminary list of annual grasses, abundant and widespread in California, that pose significant threats to wildlands. Information is requested to support further definition of this category in next List edition.

Considered But Not Listed: Plants that, after review of status, do not appear to pose a significant threat to wildlands. Plants that fall into the following categories are not included in the included in the List:

Plants found mainly or solely in disturbed areas, such as roadsides and agricultural fields.

Plants that are established only sparingly, with minimal impact on natural habitats.

C. Invasive Exotic Pest Plants in Tennessee (May 2001) Tennessee Exotic Pest Plant Coouncil

Rank 1. Severe Threat – Exotic plant species that possess characteristics of invasive species and spread easily into native plant communities and displace native vegetation.

Rank 2. Significant Threat – Exotic plant species that possess characteristics of invasive species but are not presently considered to spread as easily into native plant communities as those species listed as Rank 1 - Severe Threat.

Rank 3. Lesser Threat – Exotic plant species that spread in or near disturbed areas and are not presently considered a threat to native plant communities.

Watch List. –A. Exotic plants that naturalize and may become a problem in the future; includes species that are or could become widespread in Tennessee. At this time more information is needed and there is no consensus about their status.

Watch List: - B - Exotic plant species that are severe problems in surrounding states but have not been reported in Tennessee.

D. Invasive Alien Plant Species of Virginia (published June 1999) Department of Conservation and Recreation\Division of Natural Heritage and the Virginia Native Plant Society

About the List DCR Natural Heritage and Virginia Native Plant Society use detailed criteria to assess the invasiveness of a plant. Factors used to rank each species include: cumulative impacts on natural areas; potential to disperse and invade natural landscapes; distribution and abundance; difficulty to manage; and impacts on other species. The list is periodically reviewed and updated by land managers, nurserymen, landscape architects, horticulturalists, botanists, wildlife biologists, and other conservation partners.

II. Invasiveness Ranking

Each species on the list is assessed according to its cumulative effects on natural areas and native plant habitats where it typically occurs.

The A-ranked species exhibit the most invasive tendencies in natural areas and native plant habitats. They may disrupt ecosystem processes and cause major alterations in plant community composition and structure. They establish readily in natural systems and spread rapidly.

The B-ranked species exhibit moderate invasiveness in natural areas. They may have minor influence on ecosystem processes, alter plant community composition and affect community structure in at least one layer. They may become dominant in the understory layer without threatening all species found in the community. These species usually require a minor disturbance to become established.

The C-ranked species generally do not affect ecosystem processes but may alter plant community composition by out-competing one or more native plant species. They often establish in severely disturbed areas. The disturbance may be natural or human origin, such as ice-storm damage, wind-throw, or road construction. These species spread slowly or not at all from disturbed sites.

III. Management Guidelines and Manuals

A. Exotic Plant Guidelines, North Carolina Division of Parks and Recreation Department of Environment and Natural Resources (published February 1, 1998)

Definitions, Exotic species: A species occurring in a given place that is outside of its native range. Exotic, non-native, non-indigenous, introduced, and alien are synonymous term. The vast majority of exotic species have little or no impact on our natural areas, and many are highly beneficial. Almost all of our important crops are exotic species that were deliberately introduced.

Invasive exotic species: A species outside of its native range that threatens the survival or reproduction of native plants or animals or threatens to reduce biological diversity. Invasive exotic species will be considered for active control in our state parks.

B. Wisconsin's Invasive Plants, Wisconsin Department of Natural Resources (May 1999)

Invasive Species Defined Most invasive species are ecological pioneers and colonizers which, once introduced, quickly establish themselves in ecologically disturbed communities. Invasive species typically displace native flora due to faster growth rates, efficient dispersal mechanisms, and tolerance of a wider range of conditions. Invasive species often lack natural predators and diseases which control populations in their native environments. As the diversity and populations of native plants decrease, so does the variety of habitats available for wildlife.

For the purposes of this manual, invasive species are described as either exotic (alien), translocated, or opportunistic. Exotics are primarily European and Asian species that have been intentionally or accidentally introduced to North America. Translocated species are native North American species whose pre-settlement range either did not include Wisconsin, or did not include certain areas of Wisconsin in which they are now a problem. Opportunistic species are native colonizers which can dominate certain natural communities and decrease species diversity. Some native species, such as cattails (Typha spp.), have historically inhabited Wisconsin natural communities in lower numbers, but have become more widespread with increased disturbance and sedimentation in wetlands. Such situations often occur when environmental conditions change, or when natural processes are restricted or eliminated (e.g. suppression of wildfires).

C. Vegetation Management Manual (Illinois Nature Preserve Commission)

Alien (Exotic) and Opportunistic Native Species There are two kinds of troublesome plant species in natural areas. Members of the first group are called aliens or exotics. These are plants that are not native to the flora of the region in which they are found. Often, these plants were introduced from Europe or Asia accidentally, or for horticultural or other purposes. Members of the second group are called opportunists. They are plants that are native components of the regional flora, but that have become overly abundant and/or aggressive due to environmental conditions that are different than conditions before European settlement (e.g., heavy grazing, lack of fire, or creation of disturbed habitats).

IV. Policy and Law

A. Executive Order 13112 on Invasive Species

(a) "Alien species" means, with respect to a particular ecosystem, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem.

(b) "Control" means, as appropriate, eradicating, suppressing, reducing, or managing invasive species populations, preventing spread of invasive species from areas where they are present, and taking steps such as restoration of native species and habitats to reduce the effects of invasive species and to prevent further invasions.

(c) "Ecosystem" means the complex of a community of organisms and its environment.

(e) "Introduction" means the intentional or unintentional escape, release, dissemination, or placement of a species into an ecosystem as a result of human activity.

(f) "Invasive species" means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.

(g) "Native species" means, with respect to a particular ecosystem, a species that, other than as a result of an introduction, historically occurred or currently occurs in that ecosystem. (h) "Species" means a group of organisms all of which have a high degree of physical and genetic similarity, generally interbreed only among themselves, and show persistent differences from members of allied groups of organisms.

B. Federal Noxious Weed Act of 1974

Sec. 2802. Definitions

(c) ''Noxious weed'' means any living stage (including but not limited to, seeds and reproductive parts) of any parasitic or other plant of a kind, or subdivision of a kind, which is of foreign origin, is new to or not widely prevalent in the United States, and can directly or indirectly injure crops, other useful plants, livestock, or poultry or other interests of agriculture, including irrigation, or navigation or the fish and wildlife resources of the United States or the public health.

Amendments to the Federal Noxious Weed Act (1990)

Amendments to the Federal Noxious Weed Act under the 1990 Farm bill address "undesirable plants," which are defined such that they include, but are not limited to, the definition of noxious weeds.