Response of a Shrub-Steppe Ecosystem to Fire: Soil Water and Vegetational Change

A wildfire in August 1984 eliminated big sagebrush from a shrub-steppe community in southeastern Washington. Bluebunch wheatgrass dominated the community in subsequent years. By comparing leaf area index and soil water storage on the burned site with an adjacent unburned site containing big sagebrush, we were able to test the hypotheses that plant community structure controls soil moisture dynamics and that wildfire can alter the water balance in these arid landscapes. Elimination of big sagebrush from the landscape greatly reduced the community leaf area index. Soil water storage computed to a depth of 125 cm was not affected by the change in community structure. However, storage computed to a depth of 275 cm was significantly greater on the burned site compared to the unburned site. This difference increased with time after the fire. Wildfire in shrub-steppe communities dominated by big sagebrush effectively removes the deep rooted, woody component from these ecosystems. Consequently, the ability of the vegetation to remove stored soil water is inhibited by a reduction in the ability to access deeply stored soil moisture.