6 Impacts of Invasive Plants on Community and Ecosystem Properties Lawrence R. Walker and Stanley D. Smith Salt-cedar (Tamarix sp.) Invasive indigenous (IN) or nonindigenous (NI) plant species can alter various properties of plant communities, including species di- versity, primary productivity, interactions between species, stability, and rates or path- ways of successional recovery of a community following disturbance (Ramakrishnan and Vitousek 1989; Versfeld and van Wilgen 1986; Vitousek 1990; Vitousek and Walker 1989; Walker and Vitousek 1991). They can also alter the actual disturbance regime (Breytenbach 1986; Hughes et a1. 1991; Vitousek 1990). Studies of ecosystem pro- cesses are usually not focused on a particular organism but on the linkages between or- ganisms and their environment. Examination of the flow of energy, water, or nutrients through an ecosystem can provide a sensitive measure of the degree to which invasive plants alter indigenous ecosystems. Successful management of communities and ecosystems containing invasive species involves (1) assessing whether the invaders have signifi- cantly altered the ecosystem from its preinvasion condition, (2) recognizing and measuring specific community and ecosystem properties potentially being altered by the invader, and (3) developing strategies that return communities and the associated ecosystem processes to the preinvasion state (if such is deemed desirable by management goals). 69 J. O. Luken et al. (eds.), Assessment and Management of Plant Invasions © Springer-Verlag New York, Inc. 1997