Affiliation:
1. Department of Botany and Plant Ecology Weber State University Ogden Utah 84401 USA
2. Department of Mathematics Weber State University Ogden Utah 84401 USA
3. 2914 Central Street SE Olympia Washington 98501 USA
4. U.S. Geological Survey Forest & Rangeland Ecosystem Science Center Corvallis Oregon 97330 USA
5. Department of Botany & Plant Pathology Oregon State University 2082 Cordley Hall Corvallis Oregon 97331 USA
Abstract
AbstractPremiseDryland 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.
Subject
Plant Science,Genetics,Ecology, Evolution, Behavior and Systematics