Sulfur deposition will continue to decrease and subsequently have less of a negative impact on forest ecosystem nutrient cycling, whereas future nitrogen deposition will be beneficial to most southern forests, which are nitrogen limited.
High-elevation spruce-fir forests in the Southern Appalachian Mountains are the only forests in which significant damage is linked to acid deposition.
The overall health of hardwoods, oak-pine, and southern pine forests has not been shown to be adversely affected by acid deposition.
Regionally, there is no evidence that acid precipitation is causing significant damage to stream chemistry in the Southern United States. Water quality in some streams in the Southern Appalachian Mountains is decreasing.
Ozone-related annual growth reductions for pine seedlings across the South are probably between 2 and 5 percent. Tree-water stress or forest drought is thought to protect seedlings from the negative effects of ozone. Any protective benefits provided by drought stress for seedlings are likely offset by growth and productivity reductions.
Southern pines typically do not show visible symptoms of ozone (O3) injury under ambient O3 conditions, but growth of mature southern yellow pines is being reduced by current ambient ozone levels at annual rates that vary from 0 to 10 percent per year.
Continued increases in ozone concentrations will likely have significant negative impacts on pine forests in the South.
Forest area and growth rates could increase across the South with moderate increases in air temperatures and carbon dioxide concentrations during the 21st century. Severe temperature increases could negatively affect forest productivity and area, especially if precipitation rates do not increase to compensate for increased water demands.
Carbon storage in southern forest ecosystems, including public, private, and industrial forests, could make a significant contribution to carbon sequestration. Future policies, incentive programs, and forest management intensity will affect carbon sequestration rates.
Land use change, not climate change or atmospheric chemistry, has been and probably will continue to be the most important determinant of carbon storage, uptake, and release in terrestrial ecosystems.
Existing climate change models do not provide adequate information to forecast changes in location, extent, frequency, or intensity of extreme weather events and their impacts on forest ecosystems. Potential increases in air temperature and changes in precipitation patterns may contribute to increased frequency or intensity of some events.
Detailed spatial and temporal predictions of abiotic stressor effects on forest sustainability are not possible without long-term improvements in regional monitoring and studies designed to understand specific and integrated broad-scale stress responses at forest ecosystem, community, and species levels.
