Warmer temperatures, more extreme droughts and wet years will directly impact the abundance of plants on rangelands, alter the mix of plant species found there and change plant species’ geographic boundaries, say Utah State University ecologists. All this will, in turn, impact soils and the animals that rely on rangeland habitat.
Peter Adler, associate professor in USU’s Department of Wildland Resources and Ecology Center, and his colleagues are working to understand how historical climate variations have altered plant communities and how that information may help forecast future changes. In addition, he and Quinney Fellow Aldo Compagnoni, a doctoral student in plant ecology, are looking specifically at how changing climate may give an advantage to cheatgrass — a persistent, invasive weed that is already overrunning the American West.
“Ecosystems are difficult to predict,” says Adler, a 2011 recipient of a Faculty Early Career Development “CAREER” Award from the National Science Foundation. “Even if climate scientists could tell us exactly how precipitation and temperature will change, we still have lots of hard questions about the ecological responses. There will always be a gap between what scientists can provide and what managers need.”
In research published in a recent issue of the journal Ecology, Adler and his colleagues found changes in the amount, timing and type of precipitation (snow vs. rain), as well as temperature, impact dominant plant species in sagebrush steppe ecosystems. Those changes in the plant community imply changes in forage available for wild and domestic grazing animals, prompting new management approaches.
Agencies and land managers are accustomed to plans — those that regulate grazing allotments, for example — that are consistent from year to year.
"They may use a conservative stocking rate and just leave it in place,” Adler says. “But with more variable precipitation expected, we need to ask, ‘How do you take advantage of good years and survive the bad years?’ and that may require a more dynamic response.”
Among the many factors land managers must consider is Utah and surrounding areas will experience a growing percentage of precipitation falling as rain and less as snow. The past several years of climate data already show a steady increase in rain and decrease in snowpack.
Adler and Compagnoni have conducted experiments to examine what this will mean for range plants, especially cheatgrass — the nemesis of land managers throughout the West.
Cheatgrass (Bromus tectorum) spreads rapidly, degrades the environment and affects soil moisture, plant communities and wildlife. A cool season grass, it germinates in fall and grows during winter and spring. It develops an extensive root system in winter, so by the time other grasses and plants begin to grow; the cheatgrass has usually robbed the top foot of soil of its water.
In early summer, cheatgrass dries quickly, transforming millions of acres into extremely efficient fuel for more frequent wildfires. Those fires wipe out other vegetation, leaving soils unprotected from erosion, but cheatgrass is so resilient that it’s usually the first plant to take root again. Cheatgrass is not yet a problem at higher, cooler elevations, but that could change.
In an experiment conducted at varied elevations in northern Utah, Compagnoni found warmer temperatures improved cheatgrass performance.
“Our historical data showed cheatgrass seems to do best in low snow years and the experiment confirmed that trend,” Adler says. “We expect drier, warmer years with more pronounced mid-winter thaw. It doesn’t take much warming to lose snowpack. Our work suggests these decreases in snowpack will promote the cheatgrass invasion, at least in mid to high elevations.”
Efforts are underway in laboratories across the West to find ways to control cheatgrass, but until an effective method is devised, Adler says agencies may have to budget more money to fight the frequent fires that will accompany cheatgrass expansion.