Ten-year ecological responses to fuel treatments within semiarid Wyoming big sagebrush ecosystems

Authors: PYKE, DAVID - Us Geological Survey (USGS); SCHAFF, SCOTT - Us Geological Survey (USGS); CHAMBERS, JEANNE - Us Forest Service (FS); SCHUPP, EUGENE - Utah State University; Newingham, Beth; GRAY, MARGARET - Utah State University; ELLSWORTH, LISA - Oregon State University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2022
Publication Date: 7/19/2022
Citation: Pyke, D.A., Schaff, S.C., Chambers, J.C., Schupp, E.W., Newingham, B.A., Gray, M.L., Ellsworth, L.M. 2022. Ten-year ecological responses to fuel treatments within semiarid Wyoming big sagebrush ecosystems. Ecosphere. 13(7). Article e4176. https://doi.org/10.1002/ecs2.4176.
DOI: https://doi.org/10.1002/ecs2.4176

Interpretive Summary: Sagebrush ecosystems of western North America are threatened by invasive annual grasses and wildfires that can remove fire-intolerant shrubs for decades. Fuel reduction treatments are implemented in efforts to aid in fire suppression, conserve wildlife habitat, and restore historical fire regimes. In 2005, we began examining ecosystem responses to fuel reduction treatments (prescribed fire, mowing, and herbicide applications [tebuthiuron and imazapic]) in six Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities. We evaluated the long-term effects of these fuel treatments on: (1) amount and longevity of fuel reduction; (2) Greater Sage-Grouse habitat characteristics; and (3) community resistance to annual grasses and ecological resilience. Mowing and tebuthiuron reduced woody biomass similarly, but fuel reduction from mowing was immediate whereas fuel reduction with tebuthiuron took up to six years. Tebuthiuron reduced fuel via shrub death whereas mowing maintained shrub densities near control levels. All woody fuel treatments reduced sagebrush cover to below 15 % (recommended minimum for Greater Sage-Grouse habitat) for 10 years. Median mowed sagebrush height stayed above the recommended 30 cm, but all treatments increased cheatgrass (Bromus tectorum) cover above a maximum of 10 %. Ecological resilience of Wyoming big sagebrush communities to woody fuel treatments was least for fire and greatest for mowing treatments. Poor resilience was identified by: (1) sustained reductions in cover and density of some perennial plant groups (e.g., big sagebrush and Sandberg bluegrass [Poa secunda]) with poor perennial plant recovery; (2) sustained reduced cover in lichens and mosses; and (3) increases in cheatgrass cover over the 10 years. Although 10 years was not sufficient, mowing woody fuels in arid sagebrush communities has the greatest potential to reduce woody fuel, minimize shrub deaths and soil disturbances, and maintain lichens and mosses, while minimizing long-term negative impacts on Greater Sage-Grouse habitat and maintaining community resilience and resistance. However, increases in cheatgrass cover may threaten these potential outcomes.

Technical Abstract: Sagebrush ecosystems of western North America are threatened by invasive annual grasses and wildfires that can remove fire-intolerant shrubs for decades. Fuel reduction treatments are used ostensibly to aid in fire suppression, conserve wildlife habitat, and restore historical fire regimes. In 2005, we began examining ecosystem responses to fuel reduction treatments (prescribed fire, mowing, and herbicide applications [tebuthiuron and imazapic]) in six Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities. We evaluated the long-term effects of these fuel treatments on: (1) amount and longevity of fuel reduction; (2) Greater Sage-Grouse habitat characteristics; and (3) community resistance to annual grasses and ecological resilience. Responses were analyzed using repeated measure, linear mixed models. Response variables included plant biomass, cover, density and height, distances between perennial plants, and exposed soil cover. Prescribed fire produced the greatest reduction in woody fuel over time. Mowing and tebuthiuron reduced woody biomass similarly, but fuel reduction from mowing was immediate whereas fuel reduction with tebuthiuron took up to six years. Tebuthiuron reduced fuel via shrub death whereas mowing maintained shrub densities near control levels. All woody fuel treatments reduced sagebrush cover to below 15 % (recommended minimum for Greater Sage-Grouse habitat) for 10 years. Median mowed sagebrush height stayed above the recommended 30 cm, but all treatments increased cheatgrass (Bromus tectorum) cover above a maximum of 10 %. Ecological resilience of Wyoming big sagebrush communities to woody fuel treatments was least for fire and greatest for mowing treatments. Poor resilience was identified by: (1) sustained reductions in cover and density of some perennial plant groups (e.g., big sagebrush and Sandberg bluegrass [Poa secunda]) with poor perennial plant recovery; (2) sustained reduced cover in lichens and mosses; and (3) increases in cheatgrass cover over the 10 years. Although 10 years was not sufficient, mowing woody fuels in arid sagebrush communities has the greatest potential to reduce woody fuel, minimize shrub deaths and soil disturbances, and maintain lichens and mosses, while minimizing long-term negative impacts on Greater Sage-Grouse habitat and maintaining community resilience and resistance. However, increases in cheatgrass cover may threaten these potential outcomes.