Long‐term biocrust responses to wildfires in Washington, USA

Abstract

PremiseDryland ecosystems in the western United States are affected by invasive species, wildfires, livestock grazing, and climate change in ways that are difficult to distinguish. Biocrusts perform important ecological roles in these systems and are sensitive to all of these pressures.MethodsWe revisited a Washington, USA, site sampled for biocrusts in 1999 to focus on effects of exotic annual grass invasion and wildfires in the absence of livestock grazing. We examined changes between 1999 and 2020 using a Bayesian directed acyclic graph (DAG) to interpret direct and indirect causal impacts of wildfire on perennial bunchgrasses, exotic annual grasses, and biocrusts.ResultsBetween 1999 and 2020, exotic annual grass cover increased in all plots and in unburned plots by 16% and 18%, respectively, bunchgrass cover decreased by 21% and 25%, and biocrust cover decreased by 8.9% and 9.8%. Our DAG suggested that decreases in bunchgrass increased exotic annual grass, which reduced biocrust cover. Wildfires did not directly influence changes in bunchgrass, exotic annual grass, or biocrust cover. Areas dominated by exotic annual grass had less abundant and diverse biocrusts than areas with less exotic annual grass.ConclusionsBiocrust community changes were more strongly related to increasing exotic annual grasses than to wildfires. Changes may relate to other soil disturbances or broad‐scale changes in climate or air quality. The minimal influence of wildfire on exotic annual grass and biocrusts suggests that apparent negative impacts of wildfire at other sites may be due to exacerbation by livestock grazing or other surface disturbance.

Biological soil crusts are more prevalent in warmer and drier environments within the Great Basin ecoregion: implications for managing annual grass invasion

“…The role of biocrusts in hindering invasion by annual grass may increase in importance with anticipated changes in climate. A recent study conducted by Root et al (2023), found overall loses to biocrusts on paired sites with and without fire, although they were not able to account for compounding disturbances. We anticipate the response of biocrusts to fire found by Condon et al (2023) will be corroborated by future studies, in other regions, when researchers can account for compounding disturbances.…”