Cheatgrass threatens vast regions of the American West, especially the Great Basin in Nevada and surrounding states. These are areas which were once carpeted by millions of acres of native sagebrush, perennial bunchgrasses and associated wildlife that had evolved with little herbivore pressure. Cheatgrass displaces native grasses and wildlife, can increase fire frequency and ultimately cause an irreversible loss of these native shrub-steppe communities.
This also has grazing implications: 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.
"Cheatgrass changes the fire regime, and as it spreads, can reach a tipping point," said Michael Reisner, now an assistant professor at Augustana College who led this study as a doctoral student at OSU.
"After you cross that threshold, a major rangeland fire will come through that takes out the sagebrush, and in most cases the native ecosystem never recovers," Reisner said. "Many of the plant and animal species that were there can disappear, mostly replaced by cheatgrass that offers poor forage for cattle."
In a more resistant system, abundant native bunchgrasses can limit the size and connectivity of gaps, which minimizes the water and nutrients available to cheatgrass. 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.
Cattle trampling also appeared to disturb biological soil crust that offers a second defensive barrier against cheatgrass, and further speeds the invasion. Impacts are greater on the drier and warmer sites within this region.'/>"/>
|Contact: Paul Doescher|
Oregon State University