Global climate change and introduced species in United States forests.

Introduced species already cause billions of dollars of damage annually in United States forests, plus massive ecological damage whose economic value has often not been estimated. The variety of impacts is staggering and includes herbivory, predation, disease, parasitism, competition, habitat destruction, hybridization, and changed disturbance regimes and nutrient cycles. How global climate change will affect these impacts has scarcely been assessed. Range changes of existing introduced species will be prominent, as many species' biogeographic ranges are set primarily by climate. Similarly, some species that might otherwise not have survived will be able to establish populations in a changed climate. It is more difficult to predict what the impacts of the introduced species will be. What is most needed are studies of the combined impacts of changing climate, CO2, and nutrients. Certain aspects of the biology of introduced species, such as evolution and autonomous dispersal, greatly complicate the prediction of spread and impact of introduced species.