Trends and rising threats from invasive species
Humans intentionally and unintentionally spread invasive species. The foundations of agriculture and animal husbandry are based on ancient habits of selectively favoring some plant and animal species and their habitats over others for food, fiber, and medicine (Flannery 1973). According to Pimentel and others (1999), about 50,000 non-native species have been introduced in the United States. Many nonnative species have been deliberately introduced for erosion control (kudzu), food animals and fish (brown trout), agricultural crops (Johnson grass), and ornamental trees and landscape plants (purple loosestrife). Some insects and diseases have been introduced in ignorance, as was the Gypsy Moth, or as the unintentional result of a global economy, as with the West Nile virus and Zebra mussels (Pimental and others 1999). Many invasive plants in the United States were originally introduced for food, fiber or erosion control, or as ornamentals. For example, purple loosestrife was introduced as an ornamental in the early 19th century. Loosestrife is present in riparian areas throughout the continental United States and control costs are an estimated $45 million per year. Riparian areas are extremely valuable to native plants and animals, and the wholesale invasion by Loosestrife poses a serious threat of eventual extinction to numerous riparian-dependent species (Pimentel and others 1999).

Other plant species, such as European Cheatgrass, have almost entirely displaced sagebrush-grassland plants and associated animals. Cheatgrass has also seriously altered the fire regime from an average return interval of 60-110 years to 0-3 years. Cheatgrass is an example of the adverse impacts an introduced species can have on the environment. Some scientists estimate that Cheatgrass is present on 100 million acres of grassland-steppe in the western United States. Cheatgrass forms a dense, uniform carpet that out-competes native grasses and shrubs. It greens quickly, dries quickly and produces a very flammable cover that often burns completely, without allowing native plants to reestablish. In pinyon-juniper woodlands, the combination of Cheatgrass and fire may effectively prevent the re-establishment of the original woodlands (Mitchell 2000).

Invasive species cost the public approximately $137 billion per year in damage, loss, and control (Pimentel and others, 1999). The economic losses are significant but the ecological and cultural losses of native flora and fauna are equally important. For example, the bullfrog, a nonnative species in California, has almost completely replaced the native California red-legged frog--the famed jumping frog of Calaveras County. Another introduced plant, the Giant Reed, eliminates native streamside vegetation and dries up creeks that provide habitat for four endangered species: least bell’s vireo, southwestern willow flycatcher, California red-legged frog, and unarmored three-spine stickleback (USDA Forest Service 2003a).

Approximately 46% of the plants and animals federally listed as endangered species have been negatively impacted by invasive species (Wilcove and others 1998). Introduced insects and disease have also taken their toll on the environment. Chestnut Blight and Dutch elm disease are two well-known examples. Gypsy moth was intentionally introduced in the 1800s as a possible source of silk production. As a result of these well-known pests, the American chestnut and American elm have virtually disappeared from the US landscape and numerous other eastern trees are at risk from Gypsy moth (USDA Forest Service 2001).

What is the role of the Forest Service?
The Forest Service Chief has recognized the threat that invasive species pose to forest health, the economy, and the mission of the Forest Service. The interaction between the invasive species threat and other significant threats needs to be considered. For example, accidental spread of invasive species by unregulated OHV use, the spread of invasives on newly burned areas, and the wide swaths of some invasives that fragment habitats are obvious interactions. The invasive species issue is broad and impacts almost all terrestrial and aquatic habitats nationwide.

Law and policy governing invasive species
Managing and controlling invasive species requires an extraordinary coordination of programs, research, and management actions at the federal, state, and local levels. Invasive species affect all land ownerships and jurisdictions. The U.S. Department of Agriculture alone has six agencies involved in the control of invasive species (Tenny 2002). The Federal Noxious Weed Act of 1974, as amended (7 U.S.C. 2801 et. seq.), 36 C.F.R. 222.8, Departmental Regulation 9500-10, and Forest Service Manual 2080 outline agency responsibilities for noxious weed management. (Note: not all legally defined “noxious weeds” are non-native invasive plants.) FSM 2080 provides guidance to the National Forest System to address the more narrowly defined “noxious weed management”. Forest Service responsibilities and management direction for the control of insects and disease are listed in the Cooperative Forestry Assistance Act of 1978 (92 Stat. 356; 16 U.S.C. 2101) and Forest Service Manual 3400.