Meta-analysis of the interplay of soil resources affecting ecological condition and resistance to disturbance in the sagebrush steppe, USA

Background/Question/Methods

Soil resources and their spatial patterning can be closely tied to ecosystem processes. Understanding the effects of changes in ecological disturbance regimes on soil resources, and the capacity of soil resources to resist disturbance, can therefore be important for assessing ecological condition.  In this meta-analysis, we examined the resistance of surface soil resources and their spatial patterning to disturbance by fire in sagebrush (Artemisia) steppe of North America – a biome currently experiencing increases in wildfire.  We reviewed 39 studies that reported on soil properties for sagebrush steppe with distinct microsite (undershrub and interspace) patterning that was and/or was not recently burned.  We estimated microsite effect sizes (interspace/undershrub) for 21 soil properties that included soil biogeochemical, hydrological, and physical properties. We examined the impact of burning on microsite effects by calculating mean effect sizes and associated confidence intervals for sagebrush steppe that was and was not recently burned, using a non-parametric, fixed effects categorical data model.

Results/Conclusions

Results indicated that the spatial patterning of biogeochemical resources, in which soil surfaces (microsites) beneath shrubs are enriched, is resistant to burning.  However, microsite effects for soil surface hydrologic, temperature, and erosion characteristics appeared to shift following burning.  Differences between undershub and interspace microsites in soil water infiltration and retention, as well differences in the ability for soil near the surface to buffer extreme temperatures, were reduced following burning.  Erosion regimes shifted from the predominance of water erosion on interspace microsites in sagebrush steppe that was not recently burned, to the predominance of wind erosion on undershrub microsites in sagebrush steppe that was burned recently.  These shifts appear to create negative feedback for the spatial patterning of soil resources prior to vegetation recovery, which might affect the ability for soil resources to withstand change.  These results are particularly important in the face of increasing fire frequency in sagebrush steppe ecosystems where vegetation recovery and relatively long (decades-centuries) historic fire intervals have likely reinforced the spatial patterning of soil resources.