Alternative methods for reducing sediment delivery from skid trails used for post-fire logging

Abstract:

Ground-based salvage logging after wildfires generally compacts the burned soil, reduces infiltration, and reduces surface cover, resulting in greater runoff generation and soil erosion than compared to wildfire alone. Management options to mitigate soil erosion and sediment delivery from post-fire logging sites rely on methods established for unburned conditions, where water is diverted from skid trails and other compacted surfaces such as landings, firebreaks, and roads, and infiltrates into relatively undisturbed forest soils. These techniques are well established and effective in unburned forests. However, in burned conditions, the infiltration rate of the soil is often reduced by fire, resulting in increased overland flow and often little reduction in sediment delivery to streams when the runoff is diverted onto burned soil. We used runoff experiments on skid trails in a recently burned area to compare changes in runoff and sediment outputs among five mitigation techniques, including the current standard waterbar spacing for the site conditions. Initial results suggest that adding downed wood (logging slash) in three different configurations, including across the skid trail and only at the waterbar outlet, reduced sediment concentration by increasing surface roughness and reducing runoff velocity. Increasing the frequency of waterbars had little effect on sediment delivery. These results suggest that impacts from post-fire salvage logging could be reduced by using alternative mitigation practices.