The most significant predictor variable of exotic species invasion is the amount of canopy cover in the adjacent landscape. Increasing canopy cover is positively correlated to both exotic cover and species richness. Building cover is positively correlated to percentage cover of ornamental exotics but not to total species richness. While the relationship between buffer width and cover and richness of exotic species is negative, this relationship is only significant for buffers narrower than 150m. These results suggest that buffer width, while important, is not the only important factor in determining susceptibility to invasion. The adjacent landscape context significantly influences the extent of invasion, likely by serving as both a source of exotic propagules and by providing external disturbances. We suggest that managers and others interested in conserving native riparian buffer communities focus on the landscape structure of the site to prevent future invasion by exotic plant species.

The invasion of urban forests by exotic plant species might have important consequences for species diversity and the community structure. Many "exotic" or "non-indigenous" plant species have been brought intentionally into the United States for ornamental or agricultural purposes; others have arrived accidentally, attached to pets, automobiles, shipping containers, and so on. Some of these exotic plants are considered invasive. Invasive exotic species displace native species, change the structure of native plant communities, and can have far-reaching effects on pollinator dynamics.

For more information, take a look at this short brochure about invasive exotic species.