Impacts of invasive exotics

Daehler and Strong [2] suggest that invasive exotic pose the most severe threat to native plant diversity in many nature reserves.

• Exotic plants pose a severe threat to over 7 million hectares of Federal lands in the western U.S.
  • Annual losses to leafy spurge (Euphorbia esula) - $144 million.

  • $20 million needed annually to control hydrilla (Hydrilla verticillata) in 35,000 hectares of Florida waterways.

• Mediterranean fruit fly - $100 million in 1981 to eradicate from San Francisco Bay area. (Helicopters, aerial spraying of malathion.)

• Congressional Office of Technology Assessment report ``Harmful Non-Indigenous Species in the United States,'' OTA-F-565 (Washington, D.C.: U.S. Government Printing Office, September 1993).
  • Evaluated impacts of 79 non-indigenous species (NIS) introduced from 1906-1991.

  • Cumulative losses estimated to be $97 billion.

• More recently Pimentel et al. [12] estimated that ``the approximately 50,000 nonindigenous species in the United States cause major environmental damage and losses totaling approximately $137 billion per year.''