ABSTRACT
Invasions of nonnative plants into new regions have a tremendous impact on many natural and managed ecosystems, affecting their composition and function. Nonnative invasive species have a large economic impact through lost or degraded land
use and eradication costs, and are a primary cause of extinction of native species (Vitousek et al. 1996; Mooney and Hobbs 2000; Pimentel et al. 2005). Nonnative invasive plants can affect ecosystems and land use by competitively excluding desired species and altering disturbance regimes (D’Antonio and Vitousek 1992). As a result, characterizing the prevalence of invasive species is a key element of several efforts to assess ecosystem health and sustainable management (Anonymous 1995; National Research Council Committee to Evaluate Indicators for Monitoring Aquatic and Terrestrial Environments 2000; Heinz Center 2002).
