ABSTRACT
Invasive species constitute one of the most serious threats to native biodiversity and ecosystem function. According to Wilcove et al. (1998), the spread of alien species is second only to habitat loss as a cause of species endangerment in the United States. Approximately 17,000 species of vascular plants are native to United States, but nearly 5,000 exotic species have escaped cultivation and occur in natural ecosystems (Morse et al. 1995). Many of these have become major management problems by outcompeting native species, homogenizing species composition, and altering ecosystem processes (Levine et al. 2003). In addition to displacing native species, invasion by exotic plants may reduce nutrient availability (Evans et al. 2001; Ehrenfeld 2003), alter hydrology (Loope et al. 1988), degrade wildlife habitat quality (Schmidt and Whelan 1999), and alter disturbance regimes (Gordon 1998). The economic losses and expenditures from damage and control of exotic plants are staggering. For example, exotic aquatic plants cause $10 million per year in damage and require $100 million per year for control (Pimentel et al. 2000). For a single terrestrial species, Lythrum salicaria (purple loosestrife), $45 million are spent each year on control efforts (Pimentel et al. 2000).
