Volunteers and Invasive Plants: Learning and Lending a Hand link

U.S. Fish & Wildlife Service
America's National Wildlife Refuge System

Volunteers and Invasive Plants: Learning and Lending a Hand

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The Big Picture

Invasive Plants Defined-What They Are and What They Are Not

The US Fish and Wildlife Service (USFWS) works to maintain desirable vegetation on the refuges they manage. This means keeping the plants they do want and controlling the plants they do not want. Depending on a refuge's land management goals, managers may want to retain nonnative plants that are not invasive, such as forage grasses for wildlife. Managers strive to maintain healthy plant communities to ensure that habitat is available for native flora and fauna.

There are many different terms for wanted and unwanted plants. Federal, state, and county agencies use different terms and even scientists are still debating use of some terms! With all the lingo being tossed around, it can be difficult to keep track of what's being talked about. Keep in mind that many of the definitions used to describe invasive species refer to plants and animals.



The USFWS, as well as other federal agencies, follow terminology in the Presidential Executive Order 13112 on invasive species, which was enacted in 1999.

Executive Order 13112

Alien Species

With respect to a particular ecosystem, an alien species is any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem.

Knapweed Infestation
 Photo of knapweed infestation.
View example

Invasive Species

An invasive species is an "alien species" whose introduction does or is likely to cause economic or environmental harm or harm to human health. Invasive plants are included in this definition.

Photo of silversword.
View example

Native Species

With respect to a particular ecosystem, a native species is a species that, other than as a result of an introduction, historically occurred or currently occurs in that ecosystem.


Many other definitions are commonly used by government agency personnel, scientists, and educators.

Nonnative, nonindigenous, introduced, or exotic species

These terms generally refer to a species that has been purposely or accidentally moved from its native habitat to a new location. This definition is similar to the "alien species" definition above in Executive Order 13112.

Many new plant species arrive every year, but only a few of those survive, and even fewer become established. Of the plants that do become established, most don’t affect their new environment.

Photo of Hydrilla.
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Aquatic Nuisance Species

Aquatic nuisance species are nonnative species that threaten the diversity or abundance of native species or the ecological stability of infested waters, or commercial, agricultural, aquacultural, or recreational activities dependent on such waters (1).

Read about aquatic nuisance species:

Dalmatian Toadflax
Photo of Dalmatian toadflax infestation.
View example

Noxious Weeds

Plants defined as "noxious weeds" may

  • be prohibited from being imported
  • have the potential to cause economic harm
  • be required to be controlled by the landowner (2)

Federal, state, and county agencies have developed "noxious weed lists" for their political jurisdictions.

View federal and state noxious weed lists:


  1. Aquatic Nuisance Species Task Force. <http://www.anstaskforce.gov/impacts.php> . Accessed 2006 Aug 29.
  2. Myers J, Bazely D. 2003. Ecology and Control of Introduced Plants. Cambridge (UK): University Press. 313 p.