January 10, 2011 — Vol. 27 No. 2
Goodbye sagebrush, hello to a lot more weeds?
Recent peer-reviewed papers published by Idaho State University researchers document that when sagebrush is removed from Northern Rocky Mountain areas, exotic weeds move in. The study the papers are written about occurred near Barton Road in Pocatello.
"This is something land managers and ranchers may want to keep in mind," said Matt Germino, ISU associate professor of biological sciences. "Historically, sagebrush has been eradicated from rangeland and it still is through wildfire, some management actions and other uses. Sagebrush can be thought of as a 'foundation plant species' that can sculpt the plant, animal, and microbial life around itself in many areas of the West, and its disappearance from the landscape has repercussions."
In a study "Exotic plants increase and native plants decrease with loss of foundation species in sagebrush steppe" published in the journal Plant Ecology, ISU faculty researchers Germino, Nancy Huntly and Richard Inouye, and graduate student Janet Prevéy concluded that the removal of sagebrush facilitates invasion of exotic plants, and that increased soil water is one of the causes.
"The Plant Ecology paper reports on how the whole plant community responded to the treatments, with the expected result that the weeds increase upon sagebrush removal, and the surprise that native wildflower species were lost," Germino said. "This is surprising because sagebrush removals are traditionally done to relieve native herbs from competition with sagebrush, which improves the value of a site for livestock."
In this study the researchers compared undisturbed sagebrush steppe, areas with sagebrush removed and areas where sagebrush was removed where "rainout" shelters were built that blocked out winter-spring recharge of soil water. Overall, weeds were scarce in untreated plots having native plants intact, and were three to four more times abundant in areas with the sagebrush removed. The weeds did not become nearly as abundant in areas that had the removal and the shelters.
"Our finding suggest that sagebrush plays an important role in reducing invasions by exotic plants and maintaining native plant communities, in the cold desert we evaluated," said the authors in this paper.
In related effort, Prevéy published a study in the journal Ecological Applications that showed that removing sagebrush increases certain types of exotic, noxious shrubs that can tap deeper water in the water table.
"This study further showed that when sagebrush is removed that there was not much increase at all in the desirable species like bunchgrasses, and both papers show that most of the plant community response to sagebrush removal is basically increases in exotic weeds like cheatgrass and tap-rooted forbs," Germino said.
This second paper furthermore did some detailed modeling of the exotic plant populations that revealed that their populations are not sustainable and would shrink over time unless sagebrush was removed.
"We also used rainout shelters in the experiment to block the winter recharge of deep soil water that sagebrush uses, and there were fewer exotic tap-rooted forbs in that case," Germino added. "This shows that sagebrush has some unique properties compared to other natives that can protect sites from exotic weeds. Practices like burning or chaining of large tracts of sagebrush may have benefited herb production and diversity at one point in history, but the prevalence of weeds in areas like Pocatello is complicating the outcome of these types of treatments."
Sagebrush plants have deep roots that can go deeper into the soil to tap water than grasses and wildflowers can. When sagebrush is removed, invasive species that can tap the deeper water move in.
"The results of this study argue that management of invasive plants should focus not only on removal of nonnatives but also on reestablishment of important native species," stated the authors of the study.