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Policy on the Intentional Introduction of Non-Native Species

Adopted April 23, 1999 (PDF Version)


1. The mission of the California Native Plant Society is to increase the understanding and appreciation of California's native plants and to preserve them in their natural habitat through scientific activities, education, and conservation.

2. Great economic damage and damage to native plant communities has been caused by the intentional introduction of non-native species* in California and elsewhere.

Examples of ecological and economic damage include:

  • Invasive non-native species cause up to $123 billion in economic losses in the United States each year.
  • Non-native species are implicated in the decline of 49% species (57% of plants) on the U.S. Federal endangered species list.

Examples of damaging invasive species include:

  • Tamarisk (Tamarix ramosissima and other species) were planted for streambank stabilization, windbreaks, and erosion control. This species displaces native plants and animals and disrupts hydrologic and ecological processes.
  • European beach grass (Ammophila arenaria), planted for dune stabilization, is aggressively invading dune systems throughout the west, displacing native species and communities.
  • Blue gum eucalyptus (Eucalyptus globulus) was introduced for wind breaks and fiber production. It has invaded thousands of acres of California ecosystems, displacing native species.
  • Iceplant (Carpobrotus edulis) was planted for erosion control. It too has aggressively invaded and displaced native plant communities, particularly in coastal communities.
  • Non-native trout continue to be stocked into rivers, lakes, and streams for sportfishing, where they displace and consume native aquatic species and disrupt ecosystem processes.
  • Feral pigs, released for sport hunting into California wildlands, have caused serious habitat disturbance and damage to plant communities throughout California and the west.

*For the purposes of this policy, non-native species are those species that were not present at a site prior to European contact.

3. Natural and human-caused climate change, combined with the enormous diversity and complexity of California ecosystems, make it extremely difficult to predict the impacts of any non-native species, either on the target ecosystem or adjacent ecosystems.

4. The susceptibility of California ecosystems to invasion by non-native species is increasing due to accelerating habitat fragmentation, disturbance and the ever-growing number and variety of non-native species present in California.

Therefore, it is resolved that

Because of the potential effects on native vegetation and individual native plant species, the California Native Plant Society opposes the intentional introduction or maintenance of non-native species in California wildland ecosystems unless

1. the non-native species is being used in a program to restore the health of a native ecosystem, and the non-native species has been shown by thorough testing not to persist in the target ecosystem or to spread into non-target ecosystems, or

2. the non-native species is a biological control agent intended to attack an invasive non-native organism, and has been scientifically demonstrated to pose a negligible threat to native ecosystems and species.

Partial Bibliography

California Exotic Pest Plant Council. 1998. Exotic pest plants of greatest ecological concern in California. California Exotic Plant Pest Council c/o Sally Davis, 32912 Calle del Tesoro, San Juan Capistrano, CA 92675-4227.

D'Antonio, C.M. and P.M. Vitousek. 1992. Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annual Review of Ecology and Systematics. 23: 63-87.

Dudley, T. and M. Embury. 1995. Non-indigenous species in wilderness areas: the status and impacts of livestock and game species in designated wilderness in California. Pacific Institute for Studies in Development, Environment, and Security, Oakland, CA.

Dudley, T. and B. Collins. 1995. Biological invasions in California wetlands: the impacts and control of non-indigenous species in natural areas. Pacific Institute for Studies in Development, Environment, and Security, Oakland, CA.

Pimentel, D., L. Lach, R. Zuniga, and D. Morrison. 1999. Environmental and Economic Costs Associated with Non-Indigenous Species in the United States. Cornell University web page:

Rejmanek, M. and J.R. Randall. 1994. Invasive alien plants in California: 1993 summary and comparison with other areas in North America. Madroño 41(3): 161-77.

Stein, B.A. and S.R. Flack, eds. 1996. Americas Least Wanted: Alien Species Invasion of U.S. Ecosystems. The Nature Conservancy, Arlington, VA.

U.S. Congress, Office of Technology Assessment. 1993. Harmful Non-Indigenous Species in the United States. OTA-F-565. U.S. Government Printing Office, Washington DC

Whitson, T.D., L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, and R. Parker, eds. 1996. Weeds of the West. 5th Edition. Western Society of Weed Science, Newark, CA.

Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos. 1998. Quantifying threats to imperiled species in the United States. Bioscience 48(8): 607-15.


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