|Bates, Jonathan - Jon|
|HALLETT, LAUREN - University Of Oregon|
|CASE, MADELON - University Of Oregon|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2022
Publication Date: 3/30/2022
Citation: Davies, K.W., Boyd, C.S., Bates, J.D., Hallett, L.M., Case, M.F., Svejcar, L.N. 2022. What is driving the proliferation of exotic annual grasses in sagebrush communities? Comparing fire with off-season grazing. Rangeland Ecology and Management. 82:76-85. https://doi.org/10.1016/j.rama.2022.02.009.
Interpretive Summary: Exotic annual grass invasion is a major threat to the sagebrush ecosystem. Overgrazing and fire have historically both been implicated as contributors to the exotic annual grass problem. However, experimental comparisons between grazing, especially fall and winter (off-season) grazing, and fire are lacking. We compared the effects of moderate grazing during the off-season and fire in sagebrush communities. Fire, but not grazing, substantially increased exotic annual grass abundance and cover. Annual forb abundance and cover was also greater with burning. These results suggest that fire, but not off-season grazing, is a threat to the sustainability of sagebrush communities at risk of exotic annual grass invasion. The results of this study is of interest to policy makers, land managers, wildlife biologists, and scientists.
Technical Abstract: Exotic annual grass invasion is a pressing concern in sagebrush rangelands of the western United States. Overgrazing and fire have historically both been implicated in the rise of annual grasses, but experiments that compare the effect of grazing versus fire are lacking, particularly for contemporary grazing practices such as off-season (fall and winter) grazing. We compared 1) burned and ungrazed (burned), 2) off-season, moderately grazed and unburned (grazed), and 3) ungrazed and unburned (control) treatments at five Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) sites in southeastern Oregon for half a decade. Fire, but not off-season grazing, substantially increased exotic annual grass cover and abundance. Vegetation cover and density were generally similar between grazed and control areas. In contrast, at the end of the study exotic annual grass cover and density were over fourfold greater in burned areas. Exotic annual grass became the dominant plant group in burned areas, but not in grazed and control areas. Cover and density of annual forbs, predominately non-native species, were generally greater in the burned compared with grazed and control treatments. Fire also decreased soil biological crust cover and sagebrush cover and density compared with grazed and control treatments. This study provides strong evidence that fire is a threat to the sustainability of Wyoming big sagebrush communities at risk of exotic annual grass dominance, but that off-season, moderate grazing poses little risk. However, considering the spatial extent of our study was limited, further evaluations are needed across a larger geographic area. Given that off-season grazing can decrease the probability of fire, off-season grazing may be a valuable tool to reduce the risk of exotic annual grass dominance.