Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2012
Publication Date: 9/1/2012
Citation: Davies, K.W., Bates, J.D., Nafus, A.M. 2012. Mowing Wyoming big sagebrush communities with degraded herbaceous understories: has a threshold been crossed?. Rangeland Ecology and Management. 65(5):498-505.
Interpretive Summary: Degraded Wyoming big sagebrush plant communities are often mowed in an attempt to restore native herbaceous vegetation. However, reducing sagebrush may promote exotic annual grass invasion in Wyoming big sagebrush communities. Research is therefore needed to determine if mowing increases native herbaceous vegetation or promotes exotic annual grass invasion. We evaluated mowing in five Wyoming big sagebrush communities with degraded herbaceous understories. Mowing did not increase the cover or density of native herbaceous vegetation. Exotic annual grasses and forbs increased with mowing. These results suggest that mowing, as a stand-alone treatment, does not restore native herbaceous vegetation in degraded Wyoming big sagebrush communities. Land managers can use this information to help them select and prioritize treatments to restore sagebrush communities.
Technical Abstract: Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh) plant communities with degraded native herbaceous understories occupy vast expanses of the western United States. Restoring the native herbaceous understory in these communities is needed to provide higher quality wildlife habitat, decrease the risk of exotic plant invasion, and increase forage for livestock. Though mowing is commonly applied in sagebrush communities with the objective of increasing native herbaceous vegetation, vegetation response to this treatment in degraded Wyoming big sagebrush communities is largely unknown. We compared mowed and untreated control plots in five Wyoming big sagebrush plant communities with degraded herbaceous understories in eastern Oregon for three years post-treatment. Native perennial herbaceous vegetation did not respond to mowing, but exotic annuals increased with mowing. Cover of Cheatgrass (Bromus tectorum L.), a problematic exotic annual grass, was 4.6-fold greater in the mowed than untreated control treatment in the third year post-treatment. Annual forb cover, largely consisting of exotics, was 1.8-fold higher in the mowed compared to the untreated control in the third year post-treatment. Mowing does not appear to promote native herbaceous vegetation in degraded Wyoming big sagebrush plant communities and may facilitate the conversion of shrublands to exotic annual grasslands. The results of this study suggest that mowing, as a stand-alone treatment, does not restore the herbaceous understory in degraded Wyoming big sagebrush plant communities. We recommend that mowing not be applied in Wyoming big sagebrush plant communities with degraded understories without additional treatments to limit exotic annuals and promote perennial herbaceous vegetation.