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Exotic forest pests, including insects and plant pathogens, have changed the structure of some forest types, and changed the density and composition of wildlife associated with them. Exotic plant species have also displaced native forest trees and understory plants in some areas, but the resultant effects to forest wildlife are not well described. Exotic plants have been introduced to enhance wildlife habitat, but their indiscriminant use in the past has led to serious invasions. Exotic animals have harmed some forest wildlife by displacing native species, preying on native wildlife, or damaging sensitive forest habitats. Only a small percentage of exotic species (4 to 19 percent) have been documented to cause great harm. Another 6 to 53 percent have neutral effects or their effects are not as yet documented.
A large number of potentially invasive exotic species can impact native wildlife and their habitats in the United States. New plant species continue to be imported. Approximately 6,741 plant species are recognized as weeds elsewhere in the world. Only 2,363 occur in the contiguous United States (Westbrooks 1998). In addition, an estimated 26,000 plant species are capable of becoming invasive once they are introduced into new environments (Campbell 1997). Approaches have been recommended for better predicting the invasive potential of exotic plant species (Mack 1996). They include simultaneous field comparisons between cogeners, one naturalized and one native, and following the fate of a species deliberately sown in a natural community beyond its current range, with or without environmental manipulation. Predictions may become better if several approaches are combined simultaneously.
Many of the most invasive plant species across the nation are still offered for sale (Campbell 1997). This is especially true for invasive forest exotics. About 67 percent of invasive forest vines, including kudzu, are still available for purchase along with about 90 percent of the most invasive forest trees. Federal and State governments have no unified policy for limiting entry, reacting to emergency importation threats, or fostering integrated control methods (Miller 1997). No regional agency or organization has clearly defined responsibility or jurisdiction to organize regional integrated weed management programs. Exotic pest plant councils have been formed in an attempt to address this gap, and various Federal agencies have formed the Federal Interagency Committee for Management of Noxious and Exotic Weeds. Control of exotic plants is further complicated by the fact that much of the forest land in the Southeast is privately owned. Less than 18 percent of forested land in the Southern Appalachians is publicly owned (SERAMBO 2000).
Many experts have published recommendations for dealing with the issue of exotic plants and animals (Campbell 1997, Miller 1997, Stein and Flack 1996). Recommendations include:
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