Not all fuel-reduction treatments degrade biocrusts: Herbicides cause mostly neutral to positive effects on cover of biocrusts

Abstract

In response to increasing fire, fuel-reduction treatments are being used to minimize large fire risk. Although biocrusts are associated with reduced cover of fire-promoting, invasive grasses, the impact of fuel-reduction treatments on biocrusts is poorly understood. We use data from a long-term experiment, the Sagebrush Steppe Treatment Evaluation Project, testing the following fuel-reduction treatments: mowing, prescribed fire, and the use of two herbicides: one commonly used to reduce shrub cover, tebuthiuron, and one commonly used to combat cheatgrass, imazapic. Looking at sites with high cover of biocrusts prior to treatments, we demonstrate positive effects of the herbicide, tebuthiuron on lichens with an increase in cover of 10% and trending towards slightly negative effects on moss cover. Across plots, imazapic trended towards a decrease in lichen and moss cover without being statistically significant. Mowing and prescribed fire reduced cover of mosses, with the latter leading to greater declines across sites (declines of 18% vs. 32%). Reductions in moss cover mirrored gains in cover of bare soil, which is associated with increased risk of invasion by grasses responsible for increasing fire risk. We demonstrate that the use of herbicides simultaneously reduces fuels and maintains greater cover of lichens and mosses compared with other fuel-reduction treatments, possibly reducing risk of invasion by annual grasses that are responsible for increasing fire risk.