Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

The term “non-native” generally refers to species found in the United States whose native range is outside North America. More recently, this term has also been applied to species that are native to North America, but which are now found outside their historic range. Other terms for non-native species include “alien,” “non-indigenous,” or “introduced.” The term “invasive” is also applied to many non-native species; invasive species spread aggressively into areas occupied by native species. Clearly, not all non-native species are invasive; nor are all invasive species from outside North America.

This indicator will report total area covered by non-native species. In some cases, the total area covered by any single species may be relatively low, but total area covered by all non-natives may be larger.

A useful introduction to the issue of non-native species can be found in the Office of Technology Assessment publication Harmful Non-Indigenous Species in the United States (1993; http://www.wws.princeton.edu/~ota/disk1/1993/9325_n.html).

A more recent, policy-oriented view of non-native species issues can be found in the Congressional Research Service report Harmful Non-Native Species: Issues for Congress (1999; http://cnie.org/NLE/CRSreports/Biodiversity/biodv-26.cfm).

Two state-based surveys of the kinds of non-native species and their impacts and controls can be found at http://www.ct.nrcs.usda.gov/landscp/invasive/problems.htm (Connecticut) and http://www.mdflora.org/publications/invasives.htm (Maryland).