Protection from Erosion Following Wildfire

Erosion in the first year after a wildfire can be up to three orders of magnitude greater than the erosion from undisturbed forests. To mitigate potential postfire erosion, various erosion control treatments are applied on highly erodible areas with downstream resources in need of protection. Because postfire erosion rates generally decline by an order of magnitude for each year of recovery, effective erosion mitigation treatments are most needed during the first year or two after a fire. Postfire treatments include broadcast seeding, scarification and trenching, physical erosion barriers such as contour-felled logs and straw wattles, and mulching with wheat straw, wood straw, and hydromulch. This paper summarizes data from more than seven years of studies to evaluate the effectiveness of postfire erosion mitigation treatments at the hillslope and small watershed-scale in the western U.S. Results suggest that some mitigation treatments may help reduce erosion for some, but not all, rainfall events. Generally, mulching is more effective than seeding, scarifying, or erosion barriers. For small rainfall events, reduction in first year erosion rates have been measured for engineered wood straw and straw mulch (60 to 80%), contour-felled log erosion barriers (50 to 70%), and hydromulch (19%). Grass seeding treatments have little effect on first year erosion reduction. For intense rain events (I10 greater than 40 mm h) there was little difference between treated and non-treated areas.