A preliminary test of estimating forest site quality using species composition in a southern Appalachian watershedThis article is part of a larger document. View the larger document here.
Characteristic arborescent communities of mesophytic or xerophytic species have long been recognized as indicative of forest site quality in the Southern Appalachians, where soil moisture availability is the primary environmental variable affecting productivity. But, a workable quantitative system of site classification based on species composition is not available. We devised a prototype expert system by assigning a relative moisture weight to upland forest tree species according to their position of modal occurrence on a soil moisture gradient ranging from xeric to mesic. We classified forest sites by their position on the gradient, which was quantified by an index representing the average moisture weight for all species present. We determined the relationship of the moisture index with upland oak site index on permanent plots dominated by even-aged stands of either mixed oaks (Quercus spp.) or yellow-poplar (Liriodendron tulipifera). Regression analysis indicated the moisture index was significantly (P < 0.001) associated with observed site index and explained 62 percent of its variation. Validation of the model with an independent dataset resulted in a mean absolute error in oak site index of 6.9 feet. Results of this exploratory study suggest that estimation of site index based on species composition has potential for application in mixed upland hardwood stands of the Southern Appalachians.