Predicting a Range of Changes

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Predicting a Range of Changes

Warmer temperatures and 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. 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 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 a graduate student researcher are looking specifically at how changing climate may give an advantage to an invasive weed that is already overrunning the West.

“Ecosystems are difficult to predict” Adler said. “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. For example, whether sagebrush increases or decreases in a warmer world depends not only on its direct response to temperature, but also depends on how its interactions with competitors, herbivores and pathogens are affected by temperature. There will always be a gap between what scientists can provide and what managers need.”

That knowledge gap, however, is no reason to stop trying to plan for the future, and current methods of policy making may have to undergo some changes too, Adler said. In research published in the journal Ecology, Adler and his colleagues found that 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 said. “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 that 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 Ph.D. candidate Aldo Compagnoni have conducted experiments to examine what less snowpack and warmer temperatures will mean for range plants, especially for 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. It is a cool season grass that germinates in the fall and grows during the winter and spring. It develops an extensive root system in the 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 the plants set seed and dry out completely, transforming millions of acres into extremely efficient fuel for more frequent wildfires. The range 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 in the charred earth. Cheatgrass even converts ecosystems that store more carbon than they release (carbon sinks) into carbon emitters, increasing greenhouse gas emissions. But cheatgrass is not yet a problem at higher, cooler elevations. 

In one experiment, Compagnoni built and monitored a network of open-topped chambers that raise the air temperature within them by about 1° C and planted cheatgrass seeds in each of them. The research sites, all in northern Utah, were selected to provide an elevation gradient and were located at: Golden Spike National Historic Site, Promontory (4400 ft); Green Canyon, North Logan (5000 ft) and Hardware Ranch (6000 ft) in Blacksmith Fork Canyon near Hyrum. 

“We found that the warmer temperatures improved plant performance, meaning they grew well and produced more seeds,” Compagnoni said. “That is not good news.”

There was more bad news for ecologists in results of another experiment in Green Canyon. Compagnoni and Adler equipped research plots there with infrared heaters through the winter. The experiment’s treatments were aimed at learning how snowpack impacts cheatgrass. One treatment involved leaving heaters on all the time and a second one switched heaters on only when it snowed.

“Our historical data showed that cheatgrass seems to do best in low snow years and the experiment confirmed that trend,” Adler said. “We expect drier, warmer years with more pronounced mid-winter thaw. It doesn’t take much warming to lose snowpack. Our work suggests that these decreases in snowpack will promote the cheatgrass invasion, at least in mid to high elevations.”

Snowpack insulates the soil, allowing decomposition to continue and protecting soil and the roots it holds from hard freezes. Thinning snowpack may be a problem for other plants because they will lose some of that protective blanket and be more susceptible to cold air temperatures. Cheatgrass, on the other hand, thrives with less snow which gives it another advantage over neighboring plants. “Aldo found higher cheatgrass mortality under snowpack,” Adler said. “It’s possible that snow mold is causing that negative affect. Whatever the cause, we expect that less snow will mean more cheatgrass.”

Efforts are underway in laboratories across the West to find ways to control cheatgrass, but until an effective method is devised, Adler said agencies may have to budget more money to fight the frequent fires that will accompany cheatgrass expansion. Again, more bad news for everyone and every plant except the cheatgrass.”

Contact: Peter Adler, peter.adler@usu.edu

Writer: Lynnette Harris, 435-797-2189, Lynnette.Harris@usu.edu


Read More in Utah Science magazine, volume 66