Homogenization of the Soil Surface Following Fire in Semiarid Grasslands

Semiarid grasslands accumulate soil beneath plant islands that are raised above bare interspaces. This fine-scale variation in microtopographic relief is plant-induced and is increased with shrub establishment. Research found that fire-induced water repellency enhanced local-scale soil erosion that reduced variation in microtopographic relief, suggesting that fire may counteract vegetation-driven, fine-scale spatial soil heterogeneity. This article analyzes longer-term measurements (up to 9 yr) of soil microtopography to evaluate the hypothesis that fire in semiarid grasslands results in more homogenous soil microtopographic relief. Changes in soil microtopographic relief were measured prior to and following a total of five fires at three semiarid grasslands within central New Mexico, United States. The fires included three cool-season prescribed fires, a warm-season prescribed fire, and a warm-season wildfire. Four of the five fires resulted in significantly lower soil microtopographic variation that persisted for up to 4 yr. The duration and magnitude of the soil leveling effect was lowest in the grassland with clay-rich soils, indicating a possible soil texture interaction. Although two grasslands had net soil loss following fires, no net erosion occurred at the third grassland, indicating that redistribution of soils can occur without net erosion. These results show that management with prescribed fire reduces biotic-driven variation in soil microtopographic relief in semiarid grasslands that may help limit the transition to shrubland ecosystems in this region.