Relationship between post-fire soil surface morphology and vegetation recovery in the sagebrush steppe

Background/Question/Methods

The semi-arid shrublands of southeastern Idaho are prone to wind erosion following wildfire. Without the protective cover of vegetation, erosion via wind is increased. In turn, geomorphic changes related to erosion and deposition may affect vegetation recovery. It is therefore of interest to understand plant recovery on soil surfaces patterned by erosive and depositional processes. The aims of this study were to determine the types of soil surface morphology present following wildfire, the heterogeneity in the soil surface, and the physical nature of the soil surface types. In addition, we examined how abundance of plant species corresponded with the soil surface heterogeneity. Field studies were conducted during the summer of 2008 at the sites of two adjacent, fall 2007 wildfires on the Snake River Plain of southeastern Idaho. Soil surface heterogeneity was determined using a fully stratified point-intercept method to find cover of each soil surface type. Physical properties of soils, including mechanical strength (penetrability), water infiltration rate, erodible mass, and volumetric water content were examined on each soil surface morphological type. Plant abundance on each surface type was found using a 0.5m² quadrat.

Results/Conclusions

Using Eckert’s 1986 classification, the burned landscape was characterized by a mosaic of coppice and playette surface morphologies. We speculate that coppices and playettes result from depositional and erosive processes, respectively. The landscape was nearly equally comprised of playette (47.9% ±0.9) and coppice (52.0% ±0.9) surfaces, and volumetric water content was similar on both surfaces (~11%). Mechanical strength of soil surfaces was greater on playettes (2.56 kg/cm² ±0.21) than on coppices (0.30 kg/cm² ±0.09), and infiltration time for water was over ten times longer for playettes than for coppices. Coppices had more than five times greater erodible mass than playettes. Mean abundance of all plants, graminoids, and forbs was about three times greater on coppice surfaces than on playette surfaces, and shrubs were found only on coppices. Playette and coppice soil surface morphologies differ in their physical and vegetation characteristics. Our data suggest that post-fire soil surface heterogeneity is associated with plant community composition, in addition to vegetation abundance. The interaction of geomorphic and vegetation patterns appears likely to sustain or promote heterogeneity in plant cover in the post-fire environment.