Title: Influence of long-term livestock grazing exclusion on the response of sagebrush steppe plant communities to fire Authors
Submitted to: Extension Reports
Publication Type: Experiment Station
Publication Acceptance Date: May 1, 2008
Publication Date: June 1, 2008
Citation: Davies, K.W., Svejcar, A.J., Bates, J.D. 2008. Influence of long-term livestock grazing exclusion on the response of sagebrush steppe plant communities to fire. Extension Reports. Range Field Day 2008 Progress Report. Oregon State University Agricultural Experiment Station, Special Report 1085. Burns, OR. pp. 3-8. Interpretive Summary: Considerable controversy exists over the use of both livestock grazing and fire on sagebrush steppe rangeland. Some groups advocate removing livestock and allowing fires to occur at more frequent intervals to mimic pre-European settlement conditions. We evaluated the impacts of fire on sagebrush rangeland, which had either been grazed up until the year of burning (1993) or had been excluded from grazing since 1937. Vegetation characteristics were measured in the 12th through 14th years after burning. Burning caused a huge increase in cheatgrass (an invasive annual grass) in the ungrazed areas, but not in the grazed areas. The increase in cheatgrass coincided with mortality of the native perennial bunchgrasses. This might not have been a problem prior to the introduction of annual invaders such as cheatgrass, but under current conditions it probably prevents the recovery of the sagebrush rangeland. This information should be of interest to scientists and land managers interested in grazing and fire interactions and preventing exotic plant invasions.
Technical Abstract: Livestock grazing of sagebrush steppe plant communities has been considered to have negative impacts because these communities did not evolve with large herbivores. The best management of these ecosystems has been assumed to be accomplished by mimicking historic conditions, i.e. reconstruct historic disturbance patterns. However, the introduction of invasive plants or altered environmental conditions has potentially changed the response of plant communities to disturbance. We evaluate directing the management of Wyoming big sagebrush plant communities based on their historic disturbance regime, ungrazed with infrequent fire, compared to other disturbance regimes. Treatments were ungrazed (grazing excluded since 1936) unburned, grazed unburned, ungrazed burned (burned in 1993), and grazed burned. Vegetation cover, density, and biomass production was measured the 12th, 13th, and 14th year post-burning. Long-term grazing exclusion followed by burning resulted in a substantial cheatgrass invasion. The ungrazed burned treatment had the least perennial vegetation and greatest annual vegetation. The ungrazed unburned and grazed unburned treatments had relatively similar vegetation characteristics. Our results suggest that long-term grazing exclusion weakens the ability of Wyoming big sagebrush plant communities to tolerate fire and thus, allows cheatgrass invasion. Low to moderate grazing by domestic livestock appears to be better management than grazing exclusion. Deviations from historic conditions can alter ecosystems response to disturbances, therefore restoring the historic disturbance regime is not the best management strategy for all ecosystems.