Multiscale responses and recovery of soils to wildfire in a sagebrush steppe ecosystem

Ecological theory predicts a pulse disturbance results in loss of soil organic carbon and short-term respiration losses that exceed recovery of productivity in many ecosystems. However, fundamental uncertainties remain in our understanding of ecosystem recovery where spatiotemporal variation in structure and function are not adequately represented in conceptual models. Here we show that wildfire in sagebrush shrublands results in multiscale responses that vary with ecosystem properties, landscape position, and their interactions. Consistent with ecological theory, soil pH increased and soil organic carbon (SOC) decreased following fire. In contrast, SOC responses were slope aspect and shrub-microsite dependent, with a larger proportional decrease under previous shrubs on north-facing aspects compared to south-facing ones. In addition, respiratory losses from burned aspects were not significantly different than losses from unburned aspects. We also documented the novel formation of soil inorganic carbon (SIC) with wildfire that differed significantly with aspect and microsite scale. Whereas pH and SIC recovered within 37 months post-fire, SOC stocks remained reduced, especially on north-facing aspects. Spatially, SIC formation was paired with reduced respiration losses, presumably lower partial pressure of carbon dioxide (pCO(2)), and increased calcium availability, consistent with geochemical models of carbonate formation. Our findings highlight the formation of SIC after fire as a novel short-term sink of carbon in non-forested shrubland ecosystems. Resiliency in sagebrush shrublands may be more complex and integrated across ecosystem to landscape scales than predicted based on current theory.

Automated summary

This study investigates the response of sagebrush shrublands to wildfire and finds that the extent and nature of the response vary with ecosystem properties and landscape position. Consistent with ecological theory, wildfire leads to an increase in soil pH and a decrease in soil organic carbon (SOC). However, the decrease in SOC is more pronounced in north-facing aspects compared to south-facing ones. In addition, the study discovers the formation of soil inorganic carbon (SIC) after fire, which differs significantly with aspect and microsite scale. These findings suggest that ecosystem recovery after wildfire is more complex and integrated across scales than previously believed.