Effects of Landform on site index for two mesophytic tree species in the Appalachian Mountains of North Carolina, USA
The effects of soil and topographic variables on forest site index were determined for two mesophytic tree species, northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) in the Southern Appalachian Mountains of North Carolina. Stand variables included soil solum thickness, soil A-horizon thickness, elevation, aspect, slope gradient, and landform index. Landform index is a recently devised environmental variable that has been used to quantify the influence of topography surrounding a stand on productivity. Regression analysis indicated that among the variables only landform index had a significant (P < .05) relationship with site index and explained 46 percent of the variation for northern red oak and 56 percent for yellow poplar. Plot data from this study were also used to validate a previously developed prediction equation for estimating yellow-poplar site index and results indicated that unbiased estimates would be within 2.5m. Results from this study suggest that landform accounts for variation in site index of mesophytic species in mountainous terrain that is not explained by conventional stand variables associated with soil and topography.