Water Repellency and Fire in Sagebrush Ecosystems of the Northern Great Basin, USA

Severe wildfires have occurred across the western United States over the past decade. Past management practices and fire suppression policies have left wild lands with high fuel loads resulting in larger wildfires with high burn severities. An estimated $40 million is spent every year in the United States to mitigate the effects of wildfires and reduce the risk of flash floods and debris flows. Past research in forested and chaparral- dominated communities has indicated that wildfires cause a significant increase in soil water repellency resulting in more runoff and erosion potential. Little data exists for other shrub lands and grasslands, therefore findings from forests and chaparral are extrapolated to the post-fire management of many other plant communities. A series of studies were conducted to better understand the impacts of wildfire and subsequent recovery on hillslope runoff and erosion processes within steep watersheds with coarse-textured soils and sagebrush-bunchgrass plant communities. In general, year to year changes in infiltration capacity have been larger than the impact of fire on infiltration due to natural variations in soil water repellency. Under dry conditions, soil water repellency can be greater and more persistent on unburned areas compared to burned areas. Recovery in years following fire can result in less water repellency, improved infiltration capacities and reduced runoff amounts compared to unburned conditions. However wildfires do consume organic ground cover that protects the soil surface, thus runoff can easily move down slope with greater velocity and erosion potential. These results suggest that postfire treatments within these plant communities should focus on erosion control and not on improving infiltration capacity by "breaking-up" soil water repellent layers within the soil.