The forest ecosystems of the southern United States are the region’s predominant land use and comprise vital resources of economic and biological significance. These forests, covering 85 million hectares or 40 per cent of the land area, are subject to numerous physical and chemical stressors. Temperature, precipitation, and nutrition are three factors that currently limit forest ecosystem health and productivity in the region. In a changing global environment, these forest ecosystems face an unprecedented rate of change and will be directly and indirectly affected by additional stresses from air pollutants and climate change, including increasing concentrations of carbon dixoide, methane, other trace gases and atmospheric aerosols, and altered land use patterns. The research presented in this book provides a sound scientific basis for management and policy decisions regarding the productivity and sustainability of forest ecosystems in the context of a rapidly changing global environment. This volume is a synthesis of five years of field and laboratory research on southern forests conducted by the U.S. Department of Agriculture Forest Service to provide scientific assessments to the US. Global Change Research Program. The book will provide scientific information for policy makers and land use managers. It will also be of interest to researchers in the environmental disciplines of ecology, forestry, atmospheric science, hydrology, soil science, and biogeochemistry.