Document: AMY-3-34-17

Will changing the amount of timing of precipitation affect plant species composition in sagebrush steppe?

MORRIS, A.N.* and J.E.ANDERSON

Idaho State University, Pocatello, ID 83209 USA ¹

Abstract:
Sagebrush (Artemisia) steppe in the Intermountain West typically is dominated by shrubs with an understory of perennial bunchgrasses and forbs. The semi-arid climate has most precipitation during winter and spring. Climatic change models predict increased precipitation during either summer or winter-spring. A shift in timing and amount of precipitation may affect plant species composition. We predicted that increased summer precipitation would increase relative cover of perennial grasses, especially rhizomatous species. Increased winter precipitation likely would maintain current species composition. These predictions were tested by measuring plant cover on plots receiving ambient precipitation or 200 mm of additional irrigation in either summer or winter (applied late fall). When established in 1997, plots did not differ in species composition. In 1998, summer and winter irrigated plots had higher native grass cover than ambient plots (p=0.013), with similar results in 1999. However, in 1999 summer irrigated plots showed a trend towards increased rhizomatous grass cover (p=0.089) with cover of 10%, 6%, and 4% for summer, winter, and ambient plots, respectively. Cover of Bromus tectorum, an invasive exotic, was higher on winter irrigated than ambient or summer plots (p=0.011) with 3.7%, 1.5%, and 0.5% cover, respectively. These results indicate that increased precipitation will increase the abundance of perennial grasses in this sagebrush steppe, but timing will affect the balance between tussock and rhizomatous forms. Additional winter precipitation may facilitate cheatgrass invasion.

Keywords: plant species composition, precipitation change, sagebrush steppe

This abstract is being presented at: 3:30 PM in session:
CLIMATE CHANGE