Impacts of wildfire on soil hydrological properties of steep sagebrush-steppe rangeland

In late August 1996, a wildfire swept across the sagebrush-dominated foothills above Boise, Idaho. Fire impacts on infiltration and inter-rill erosion were examined 1 year following the fire with simulated rainfall. Densely vegetated north-facing slopes were compared with sparsely vegetated south-facing slopes under both burned (moderate and high severity) and unburned conditions. Both fire severity and slope aspect strongly influenced the impact of fire on infiltration capacity and soil erodibility. South-facing slopes had the least infiltration and the greatest rates of erosion following the fire. Infiltration rate was significantly less and cumulative sediment yield was significantly greater on severely burned south slopes as compared with those experiencing only moderate burn severity. Fire severity had little effect on infiltration and erosion of north-facing slopes. Despite differences in final infiltration rates, runoff from plots of all treatment combinations (burned and unburned slopes) began within 2-4 min following the start of simulated rainfall. Post-fire microtopography (surface roughness, dependent on pre-fire plant community) and associated ground cover appear to be important determinants of the potential for increased runoff and interrill erosion under conditions of dry antecedent soil moisture on these steep rangelands.