In response to increasing fire in sagebrush steppe ecosystems of the Intermountain West (USA), fuel reduction treatments are being used to minimize large fire risk. Biological soil crusts (biocrusts) are a key ecological component within the sagebrush steppe. A living soil-surface community composed of moss, lichen, algae, cyanobacteria, and fungi, biocrusts contribute to soil nutrient cycles, hold soil particles together to reduce erosion, and retain soil moisture for use by vascular plants. Although biocrusts are associated with reduced cover of fire-promoting, invasive grasses such as cheatgrass (Bromus tectorum L.), the impact of fuel reduction treatments on biocrusts are poorly understood. We use lichen and moss cover and soil cover data from a long-term experiment, the Sagebrush Steppe Treatment Evaluation Project (SageSTEP), 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. Data were analyzed using linear mixed models and repeated measures.
Results/Conclusions
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% compared to control plots. Across plots, imazapic trended towards a decrease in lichen and moss cover without being statistically significant. However, imazapic treatments by chance had lower pretreatment biocrust cover than other treatments that could partially explain these trends. Mowing and prescribed fire reduced cover of mosses, with the latter leading to greater declines across sites (declines of 18% versus 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. Our findings provide justification for the inclusion of biocrusts when deciding upon appropriate fuel reduction treatments, suggesting that surveying for biocrusts prior to treatment could inform which treatment is most likely to maintain cover of biocrusts in addition to vascular plants.