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

Authors: LOHSE, KATHLEEN - IDAHO STATE UNIVERSITY; PIERSON, DEREK - IDAHO STATE UNIVERSITY; PATTON, NICHOLAS - IDAHO STATE UNIVERSITY; SANDERMAN, JONATHAN - IDAHO STATE UNIVERSITY; HUBER, DAVID - IDAHO STATE UNIVERSITY; FINNEY, BRUCE - IDAHO STATE UNIVERSITY; FACER, JEREMY - IDAHO STATE UNIVERSITY; MEYERS, JARED - IDAHO STATE UNIVERSITY; Seyfried, Mark

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2022
Publication Date: 12/23/2022
Citation: Lohse, K., Pierson, D., Patton, N., Sanderman, J., Huber, D., Finney, B., Facer, J., Meyers, J., Seyfried, M.S. 2022. Multiscale responses and recovery of soils to wildfire in a sagebrush steppe ecosystem. Scientific Reports. 12. Article 22438. https://doi.org/10.1038/s41598-022-26849-w.
DOI: https://doi.org/10.1038/s41598-022-26849-w

Interpretive Summary: Common ecological theories suggest that there is loss of soil organic carbon (that is, organic matter) following wildfire distrubance, and that emission of carbon dioxide (CO2) resulting from respiration of reestablishing plants and microorganisms exceed CO2 uptake by plant photosynthesis. Studies following the Soda Creek Fire that burned 279,000 acres of sagebrush rangeland within and around the Reynolds Creek Experimental Watershed and Critical Zone Observatory in southwestern Idaho were conducted to test these theories. Consistent with these theories, we did observed a decrease in soil organic carbon following the fire, but it varied with position within the topography and proximity to plants. However, there was no observed increase in CO2 emission from the soil as expected. Observed differences in carbon dynamics caused by the fire were largely recovered within 37 weeks post fire. Findings from this study indicate that disturbance models may need modification to address slope and vegetation differences across the landscape.

Technical Abstract: Ecological theory predicts a pulse disturbance like fire 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 the development of ecosystems where spatial and temporal scales in structure and function may not be adequately represented in conceptual models. In particular, the mountainous western US is characterized by strong topographic asymmetries at the catchment and often shrub islands of fertility at the microsite scale that are hypothesized to have different resistance and resiliencies to disturbance. Here we show that wildfire in sagebrush shrublands results in novel ecosystem responses across scales such that north facing aspects recover slower under previous shrub canopies than south-facing ones in burned spaces lacking shrubs. Consistent with ecological theory, we observed an increase in soil pH and loss of soil organic carbon (SOC) following fire but these effects varied with aspect and microsite position. In contrast to predictions, we found select formation of soil inorganic carbon (SIC) following wildfire that differed significantly with aspect and microsite scale. Spatially, SIC formation was paired with reduced respiration losses and presumably lower p(CO2) plus increased Ca2+ availability, which is consistent with geochemical models of carbonate formation. Whereas pH, mineralizable carbon, and SIC recovered to pre-burn conditions after 37 months, SOC stocks remained low. Our results indicate that a combination of conditions, higher fire temperature under shrubs, increases in soil pH, a reduction in respiration and decrease p(CO2), and increase the availability of calcium minerals from ash all regulated the formation of carbonates. Our findings highlight the formation of SIC as a novel short-term sink of carbon after fire in cold desert shrubland ecosystems and indicate that post-fire resilience of north facing aspects may be more complex and integrated across scales than predicted based on current theory.