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    Ecosystems worldwide are threatened by nonnative plant invasions that can cause undesirable, irreversible changes. They can displace native plants and animals, out-cross with native flora, alter nutrient cycling and other ecosystem functions, and even change an ecosystem's flammability (Walker and Smith 1997). After habitat loss, the spread of exotic species is considered the greatest threat to imperiled species in the United States (Flather et al. 1994; Wilcove et al. 1998; Stein et al. 2000). Many exotic invasives thrive in North America because they were introduced from other continents without natural controls, such as insect predators, plant pathogens, fungi, competing plants, and herbivores (Sheley et al. 1999). In addition, some introduced plants outcompete native species by producing allelopathic compounds that inhibit the growth of other species (Callaway and Aschehoug 2000).

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    Sieg, Carolyn Hull; Phillips, Barbara G.; Moser, Laura P. 2003. Exotic invasive plants. In: Frederici, Peter, editor. Ecological Restoration of Southwestern Ponderosa Pine Forests. Washington, DC: Island Press. p. 251-267.


    exotic, invasives, nonnative, plant invasions, ecosystems

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