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Invasion by exotic annual grasses and the excessive wildfires they promote are increasing threats to the sagebrush steppe ecosystem of the western United States. Livestock grazing may amplify the problem, since cattle trample soil biocrusts and feed on the native perennial plants that help ecosystems resist cheatgrass invasion.

A team of USGS researchers evaluated changes in plant communities over a 14-year period after livestock grazing was terminated in Browns Park National Wildlife Refuge in Colorado. After livestock were excluded, cheatgrass expanded faster than desirable perennial bunchgrasses or biocrusts, and reached levels that could lead to cheatgrass dominated grasslands. Increases in cheatgrass were highest in areas with more cheatgrass cover prior to grazing exclusion, and lowest in areas with higher initial biocrust and perennial plant cover. These results suggest that resistance to invasion could be improved through restoration, for example, using herbicides to reduce cheatgrass or seeding native perennials in areas impacted by cheatgrass.  

Germino, M.J., Kluender, C.R., and Anthony, C.R., 2022, Plant community trajectories following livestock exclusion for conservation vary and hinge on initial invasion and soil-biocrust conditions in shrub steppe: Conservation Science and Practice, e12838, Online. https://doi.org/10.1111/csp2.12838