Following habitat loss, exotic species proliferation is considered the greatest threat to our natural heritage. Invasive species encroachment is implicated in the listing of 42% of all species protected by the Endangered Species Act (Stein and Flack 1996). Invasive species cost the U.S. economy $138 billion annually (Pimental et al. 1999). Of the 83 million acres (34 million ha) managed by the National Park Service, 2.6 million acres (1.1 million ha) are infested by exotic plants and nonnative animals. Examples of nonnative animal species plaguing the parks are feral pigs and goats, hemlock woolly adelgid, New Zealand mudsnail, African oryx, and more recently mosquitoes carrying an exotic microbe, West Nile virus. To address the damage of invasive species, a National Invasive Species Management Plan was developed in 200l and is being carried out by federal agencies. The National Park Service, with its long history of fighting harmful invasives, welcomes this interagency coordination in taking on the tremendous challenge of controlling and eradicating invasive species.

The National Park Service has been a pioneer in combating threats to resources posed by invasive species. This work began with the grassroots efforts of park staff removing feral pigs at Great Smoky Mountains National Park, burros at Grand Canyon National Park (fig. 1), and purple loosestrife at Acadia National Park. As more and more invasives have encroached on parklands over the last century, the National Park Service has committed more resources, developed more complex programs and policies, and strengthened its resolve to deal with and manage invasives.