Predictions and Projections of Pine Productivity and Hydrology in Response to Climate Change Across the Southern United States

The southeastern United States is one of the most rapidly growing human population regions in continental United States, and as the population increases, the demand for commercial, industrial, and residential water will also increase (USWRC, 1978). Forest species type, stand age, and the climate all influence the amount of water use and yield from these areas (Swank et al., 1988). Because forests cover approximately 55% of the southern United States land area (Flather et al., 1989), changes in water use by forests could significantly change water yields and potentially lead to water shortages within the region. Hence, estimates of future water supply from forested areas are needed and this will require a model that can accurately predict potential change in forest wateruse at the regional scale. In addition to water resources, an accurate estimate of future loblolly pine forest productivity is essential to the development of a management plan to provide enough timber to meet consumer demand. At present, it is uncertain if the southem forests will be able to maintain (or increase) present-day levels of productivity. For example, Zahner et al., (1988) recorded a decrease in radial growth of loblolly pine (Pinus tueda) during the years from 1949 to 1984 in Piedmont stands. During the next century, substantial changes are expected to occur in a variety of environmental variables including temperature and precipitation (Melillo et al., 1989; Mitchell et al., 1989). The magnitudes of these changes are expected to vary both temporally and spatially, and they may have profound effect on forest productivity (Melillo et al., 1993) and wateruse. Although some of these changes may