Monday, 17 November 2003: 3:30 PM
Erosion after wildfires: what managers need to know
Wildfire is an ecological process and major management issue in the western U.S. What happens when the rains come after a wildfire? Erosion is a natural process that accelerates following disturbances such as wildfires. Most wildfires create a patchwork of low, moderate, and high severity burn areas, often causing spatially varied hydrologic surface conditions. Severely burned areas often have increased erosion due to loss of the protective forest floor layer and water storage as well as creation of water repellent soil conditions. Pre-fire erosion rates in a forest environment are generally small. First year surface erosion rates after the 2000 Bitterroot Valley, Montana wildfires indicate that short duration high intensity thunderstorms (10-min max. intensity 75 mm/hr) caused the highest erosion rates (2 to 40 t/ha), whereas the long duration low intensity rain events produced little erosion (0.01 t/ha). To reduce erosion and flooding potential, post-fire rehabilitation treatments are commonly used. Some mitigation treatments may help reduce erosion for some rainfall events but not all events. Our results suggest that mitigation treatments reduce erosion from low intensity rainfall events and have little effect with high intensity rainfall events.