Fig. 2. Mean monthly climatic conditions at four different locations within the southeastern USA. MAT is mean annual temperature and MAP is mean annual precipitation. Potential evapotranspiration was calculated using the Thornthwaite equation (Thornthwaite et al., 1957). Data from 1961 to 1990 (National Climatic Data Center, www.ncdc.noaa.gov/oa/ncdc.html).