Forest harvesting impacts on the non-perennial stream channels of two Landype Associations on the Appalachian Plateau

Abstract

The Monongahela National Forest in West Virginia is currently in the process ofreevaluating its riparian management guidelines for non-perennial stream channels.Quantitative data regarding the spatial extent, physical dimensions and hydraulic function ofthese stream networks is needed under control and managed conditions. 115 stream reacheswithin thirty small watersheds (<18ha) were studied for stream network configuration, channeldimensions, valley characteristics, streambed material composition and coarse woody debris(CWD) recruitment. Watersheds were selected from two landtype associations (LTAs) commonto the region and three types of forest condition (no harvest since 1920, harvested with originalbuffer standards 1980-1991, harvested with new interim buffer guidelines 1992-1996). Managedwatersheds had a variety of permanent access roads, revegetated haul roads, skid roads andtrails. Results indicate that statistically significant differences in drainage density, stream slope,and valley widths occur between LTAs. The percent by weight of particles <2mm from thestreambed also differed significantly between control reaches of the LTAs. These morphologic differences appear to influence management impacts to riparian areas. Higher drainage densityand larger valley widths on the Allegheny Plateau LTA contribute to a greater percentage ofstream length with no-buffer and an increase in the number of roads crossing streams than forsimilarly treated watersheds on the Middle Mountain LTA. The increased disturbances in theAllegheny Plateau LTA do not appear to have a measurable effect on non-perennial streambedcomposition. However, the percentage of watershed clearcut was negatively correlated with thepercentage of fine sediment (<2mm) in the streambed within the Middle Mountain LTA. Thissuggests that the probable increases in water yield from clearcut timber harvest may affect thestorage of fine sediment within the non-perennial stream channel, but that these effects may beunique to LTA. In both LTAs coarse woody debris loading was not significantly differentbetween controls and managed watersheds. Differences in the morphology of channel networksand measured impacts of past management between LTAs may have important implications forthe establishment of buffer zone policies on the Monongahela National Forest.