EFFECTS OF GLOBAL WARMING ON FORESTS

In the geologic past, natural climate changes have caused large-scale geographical shifts in species' ranges, changes in the species composition of biological communities, and species extinctions. If the widely predicted greenhouse effect occurs, natural ecosystems will respond in similar ways as in the past, but the effects will be more severe because of the extremely rapid rate of the projected change. Moreover, population reduction and habitat destruction due to human activities will prevent many species from colonizing new habitat when their old becomes unsuitable. The synergy between climate change and habitat destruction would threaten many more species than either factor alone. These effects would be pronounced in temperate and arctic forests, where temperature increases are projected to be relatively large. Localized species might face extinction, while widespread forest trees are likely to survive in some parts of their range. New northward habitat will become suitable even as die-offs of tree species occur to the south. However, it may be difficult for many species to take advantage of this new habitat because dispersal rates for tree species are very slow relative to the rate of warming, and therefore ranges of even many widespread species are likely to show a net decrease during the next century. Range retractions will be proximally caused by temperature and precipitation changes, increases in fires, changes in the ranges and severity of pests and pathogens, changes in competitive interactions, and additional effects of non-climatic stress such as acid rain and low-level ozone. Changes in species composition will have large effects on local and regional economies and biological diversity. © 1990.