A NEW study suggests that overgrazing and other factors increase the severity of cheatgrass invasion in sagebrush steppe, an endangered ecosystem in North America.
The research found that overgrazed land loses the mechanisms that can resist invasion, including degradation of once-abundant native bunchgrasses and trampling that disturbs biological soil crusts. The work was published May 13 in the Journal of Applied Ecology by researchers from Oregon State University, Augustana College and the U.S. Geological Survey.
"We think there are ways to assess the risks these lands face to reduce the impact of cheatgrass invasion," said Paul Doescher, professor and head of the Oregon State University department of forest ecosystems and society and a co-author on the study.
"In the future, we should work cooperatively with ranchers and land managers to promote a diverse sagebrush and bunchgrass ecosystem," which he said will simultaneously protect "the native plant and wildlife species and benefit sustainable rangeland use."
The researchers suggested that one of the most effective restoration approaches would be to minimize the cumulative impact of grazing by better managing the timing and frequency of grazing as well as the number of grazing animals.
The researchers also determined that, contrary to some previous suggestions, grazing does not reduce cheatgrass abundance. In this study, cheatgrass was found to be extremely tolerant of even intensive grazing, and the findings "raise serious concern" about proposals to use cattle grazing to help control its spread in areas where native bunchgrasses still persist.
Cheatgrass threatens vast regions of the American West, especially the Great Basin in Nevada and surrounding states, the Oregon State announcement said. Cheatgrass displaces native grasses and wildlife, may increase fire frequency and, ultimately, can cause an irreversible loss of these native shrub-steppe communities.
This also has grazing implications in that cheatgrass is a short-lived annual grass that dries out quickly and provides lower-quality forage for much of the year compared to perennial bunchgrasses, the announcement said.
Using data from 75 study sites, researchers found that high levels of cattle grazing were associated with reduced bunchgrass cover, with wider and more connections between the gaps that provided an opportunity for cheatgrass to invade.
If the level and amount of gaps indicate that it's necessary, changes in grazing could help restore bunchgrass cover, maintain a diversity of native grass species and provide much better resistance to cheatgrass invasion, the study concluded.
Continued research is needed to quantify the threshold levels of cattle grazing that would still maintain a healthy native ecosystem, the researchers said.