Identifying Colluvial Deposits in the Ridge and Valley Using Changes in Topography and Species Composition to Improve Estimates of Forest Site Quality.

The oak-dominated hardwood forests of the central Ridge and Valley physiographic province in southwestern Virginia are found on long parallel mountains that typically have steep side slopes and shallow soils.  As a result, the species composition of stands is dominated by more xeric species such as scarlet, chestnut, black, and white oaks. Site quality tends to be fairly low overall.  However, colluvial deposits occur at some locations on the side slopes of the mountains. There are distinct differences in topography, site quality, species composition and tree quality on colluvial soils compared to residual soils on side slopes in the Ridge and Valley.  As a result of the increased soil depth and higher site quality, certain mesic indicator species, such as yellow-poplar, tend to occur on these deposits.  The objective of this study was to identify the presence of colluvial deposits in a three-county area of the central Ridge and Valley using two methods.  The first approach was to identify the presence of yellow-poplar using differences in reflectance of yellow-poplar and oaks during leaf-out on Landsat TM imagery. The second approach was to identify the topographic signature of the colluvial soils using a GIS algorithm that identified changes in slope associated with the colluvial soils.  This information will be used to refine modeled site quality estimates of the area at a scale that is sufficient for stand-level forestry management.  This study is part of an overall project to predict upland hardwood site quality in the southern Appalachians as a function of environmental factors.