Postfire Rehabilitation Treatments: Are We Learning What Works?

Major concerns after wildfires are the increased erosion and flooding potential due to loss of the protective forest floor layer, loss of water storage, and the creation of water repellent soil conditions. Treatments to mitigate postfire erosion and runoff are commonly applied on highly erodible areas; however the effectiveness of these treatments has had limited scientific evaluation. In recent years postfire hillslope treatment effectiveness has been evaluated by using sediment fences and small catchments to directly measure sediment yields from burned hillslopes and relate those results to the specific rain events that caused them. In addition, the erosion from areas treated with various rehabilitation treatments (seeding, mulching, erosion barriers, etc.) is compared to non-treated areas. Although many of these studies are still in progress, preliminary results suggest that some mitigation treatments may help reduce erosion for some, but not all, rain events. Immediately after installation, contour-felled log erosion barriers can reduce erosion up to 70% for small rain events. For high intensity rain events (10-min max intensity of 40 mm hr^–1 or greater) there little difference in erosion reduction between treated and non-treated areas. Other studies suggest that the natural mulch provided by dead conifer needles in areas of low and moderate burn severity can reduce rill erosion by 30 to 40% and interrill erosion by 50 to 70%.