Eighty years of grazing by cattle modifies sagebrush and bunchgrass structure

Authors: Davies, Kirk; Boyd, Chad; Bates, Jonathan - Jon

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2018
Publication Date: 5/8/2018
Publication URL: https://handle.nal.usda.gov/10113/6138267
Citation: Davies, K.W., Boyd, C.S., Bates, J.D. 2018. Eighty years of grazing by cattle modifies sagebrush and bunchgrass structure. Rangeland Ecology and Management. 71(3):275-280. https://doi.org/10.1016/j.rama.2018.01.002.
DOI: https://doi.org/10.1016/j.rama.2018.01.002

Interpretive Summary: Understanding the effects of long-term, well-managed grazing on sagebrush and bunchgrass structure is important because they are the dominant vegetation in sagebrush steppe communities. To investigate the effects of long-term grazing on sagebrush and bunchgrass structure we compared nine grazing exclosures (ungrazed) with adjacent grazed rangelands. Ungrazed bunchgrasses had an accumulation of dry fuel on top of and around their base compared to grazed bunchgrasses, likely increasing their probability of mortality during a fire. Sagebrush plants were slightly smaller in the grazed compared to the ungrazed treatment. Other sagebrush structural characteristics were similar between treatments. Long-term, well-managed grazing appears to have minimal negative effects to the structure of sagebrush and bunchgrasses and are likely counterbalance by its positive effects.

Technical Abstract: Grazing by cattle is ubiquitous across the sagebrush steppe, however, little is known about its effects on sagebrush and native bunchgrass structure. Understanding the effects of long-term grazing on sagebrush and bunchgrass structure is important because sagebrush is a keystone species and bunchgrasses are the dominant herbaceous functional group in these communities. To investigate the effects of long-term grazing on sagebrush and bunchgrass structure, we compared nine grazing exclosures with adjacent rangelands that were grazed by cattle in southeast Oregon. Grazing was moderate utilization (30-45%) with altering season of use and infrequent rest. Long-term grazing by cattle altered some structural aspects of bunchgrasses and sagebrush. Ungrazed bunchgrasses had larger dead centers in their crowns as well as greater dead fuel depths below and above the crown level compared to grazed bunchgrasses. This accumulation of dry fuel near the meristematic tissue may increase the probability of fire-induced mortality during a wildfire. Bunchgrasses in the ungrazed treatment had more reproductive stems than those in the long-term grazed treatment. This suggests that seed production of bunchgrasses may be greater in ungrazed areas. Thus, grazing is likely having positive and negative effects on native bunchgrasses. Sagebrush height and longest canopy diameter was 15 and 20% greater in the ungrazed compared to the grazed treatment, respectively. However, the bottom of the sagebrush canopy was closer to the ground in the grazed compared to the ungrazed treatment, which may provide better hiding cover for ground nesting avian species. Sagebrush basal stem diameter, number of stems, amount of dead in the canopy, canopy gap size and number of canopy gaps did not differ between ungrazed and grazed treatments. Long-term, well-managed grazing appears to have minimal negative effects to the structure of sagebrush and bunchgrasses and are likely counterbalance by its positive effects.