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7 Conclusions

This Assessment highlights the integrated nature of abiotic factors that cumulatively affect overall forest health. Acid deposition does not pose a significant threat to southern forest vegetation except in the Southern Appalachian Mountain high-elevation spruce-fir forests. Nitrogen-limited forests may respond to continued nitrogen deposition with increased growth rates. Acid deposition is not causing significant damage to stream chemistry in the South. However, areas in the Southern Appalachian Mountains are showing signs of acidification.

Southern pine forest growth rates are being impacted by ambient ozone levels. For seedlings, the annual growth reductions are between 2 and 5 percent. For mature pines, the annual growth reductions are between 0 and 10 percent. Ozone effects on mature southern yellow pines have resulted in decreased growth rates. Projected 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 21^st 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 sequestration contribution. Future policies, incentive programs, and forest management intensity will affect carbon sequestration rates. However, land use change, more than changes in climate or atmospheric chemistry, has been and probably will continue to be the most important determinant of carbon storage, uptake, and release in terrestrial ecosystems. 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.