PS 27-145 - Resistance to annual grass invasion in fire-prone, cold desert shrublands: Evaluating abiotic, biotic, disturbance, and management factors

Tuesday, August 8, 2017
Exhibit Hall, Oregon Convention Center
Ann Marie Raymondi1, Nancy F. Glenn2, Robert S. Arkle3 and David S. Pilliod3, (1)Biological Sciences, Boise State University, Boise, ID, (2)Geosciences, Boise State University, Boise, ID, (3)U.S. Geological Survey, Forest & Rangeland Ecosystem Science Center, Boise, ID

Cold desert shrublands in the intermountain western United States exhibit variable resistance to invasive weeds and resilience to disturbances. Wyoming big sagebrush communities are amongst the most at-risk communities to invasion by annual grasses, resulting in altered fire regimes and the subsequent loss of native species and ecological function. Certain landscapes within mid-elevation Wyoming big sagebrush exhibit a high degree of invasion, high levels of fire activity, yet have a high conservation value. Thus, it is important to enhance our understanding of the factors that influence resistance and resilience in fire-prone landscapes in order to inform management efforts. Working within a resistance and resilience context, the objective of this study is to investigate the resistance to invasion and resilience to fire within an area of ecological importance, the Snake River Birds of Prey National Conservation Area, located in southwestern Idaho. To assess resistance and resilience, we evaluated the relative importance of abiotic, biotic, disturbance, and management factors in relation to the abundance of cheatgrass (Bromus tectorum), Sandberg bluegrass (Poa secunda), Wyoming big sagebrush (Artemisia tridentata var. wyomingensis) and biological soil crust within burned and unburned areas. This study utilized historical fire history data, post-fire rehabilitation treatment records, and present day plant community data. 


Results indicate that within burned and unburned areas, cheatgrass abundance is negatively associated with Sandberg bluegrass and biological soil crust, suggesting that early successional grasses and intact soil crust communities are amongst the few biotic characteristics within this landscape that may limit invasion. Disturbance factors such as fire frequency and fire recentness, as well as post-fire management treatments, were not found to explain cheatgrass abundance. These results reflect an abundance of research demonstrating that once Wyoming communities burn, preventing cheatgrass dominance and restoring native species can be exceedingly difficult. Within burned areas, Sandberg bluegrass was more likely to be found in areas that burned less frequently and longer ago, suggesting that it may be relatively resilient to fire and can potentially reestablish within burned areas. Results suggest, however, that drill seeding treatments may negatively impact Sandberg bluegrass, highlighting potential unintended consequences of employing rangeland drills under certain conditions in cold desert shrublands. Importantly, these results indicate that Sandberg bluegrass may limit invasion in fire-prone, Wyoming big sagebrush communities. We suggest additional research to investigate the competitive abilities of Sandberg bluegrass across temporal and environmental conditions.