Implications of exotic species invasion for restoration of urban riparian forests

I focused my research on urban riparian forests within Raleigh and Cary, North Carolina, USA. My goals are to understand the impacts of exotic species invasion on these forest communities, identify factors that make these sites susceptible to invasion, and make appropriate restoration recommendations.;First, I tested two major paradigms of current exotic species ecology using observational data from 23 urban riparian buffers. The competition paradigm was borne out by negative relationships between exotic and native species richness (r = −0.66, p = 0.0009). I also detected shifts in species composition away from native woody species in sites that have been invaded by exotic species.;My second approach involved conducting an experimental removal study at the North Carolina Museum of Art. I compared the species composition and native species recovery in three treatments: control, initially removing all vegetation and allowing regeneration, and initial removal with repeated removal of new exotic recruits. These results indicate that repeated removal is necessary to prevent invasion in urban forests but that native supplemental plantings may be necessary to create a diverse community.;My third approach involved evaluating the influence of landscape structure on patterns of exotic species invasion in urban riparian buffers. These findings suggest that processes outside the buffer, such as bird dispersal and vegetative spreading of ornamental plantings, may contribute to the invasion inside the buffer.;Exotic species invasion does have implications for restoration of urban forests. Because these forests are invaded by a suite of exotic plants, targeted efforts to remove those that are likely outcompeting native species is a good first step. Managing land use practices outside of the forests, while difficult, is necessary to reduce both the stress on the forest (e.g., fertilization) and invasion opportunities (e.g., bird dispersal, ornamental plantings). (Abstract shortened by UMI.).