OOS 2-6
Impacts of livestock removal on sagebrush vegetation communities at Hart Mountain National Antelope Refuge
The sagebrush desert is among the most endangered ecosystems in North America, due to land use changes such overgrazing by domestic livestock, invasive species, development, altered fire regimes and changing climate, which often interact to affect ecosystem structure and function. The long-term effects of domestic livestock and patterns of recovery following their removal are poorly understood in sagebrush ecosystems. A unique opportunity exists to examine the effects of livestock removal at Hart Mountain National Antelope Refuge (HMNAR), where cattle were removed to promote wildlife habitat in 1990. An understanding of the resultant changes in species composition, structure, and diversity will provide valuable information not only to refuge managers, but to land managers and other stakeholders in the Great Basin and semiarid west. To address this issue, we obtained historical data and photos from permanently located plots and photo points (N=28) in four widespread communities: (1) Mountain shrub dominated by antelope bitterbrush (Purshia tridentata)-mountain sagebrush (Artemisia tridentata subsp. vaseyana); (2) mountain big sagebrush (A. tridentata subsp. vaseyana); (3) Wyoming big sagebrush (A. tridentata subsp. wyomingensis); and (4) low sagebrush (A. arbuscula). All historical plots were previously measured in 1968, 1979, and 1987. We resampled and re-photographed all plots in 2013.
Results/Conclusions
Across all sagebrush ecosystem types there was a decrease in bare ground (P<0.01) following cattle removal, with concomitant increases in shrub, native bunchgrass, and biological soil crust cover that varied by community type. Low sage (A. arbuscula) communities had increased shrub cover (P=0.06) and decreased bare ground (P<0.01) in 2013 compared to years when the refuge was grazed. Mountain big sage (A. tridentata ssp. vaseyana) communities had higher bunchgrass (P<0.05) and lower litter cover (P=0.03) in 2013 than in prior sampling years. Wyoming big sage (A. tridentata ssp. wyomingensis) communities had increased shrub cover (P<0.01) in 2013 than in years when the refuge was grazed, but no changes in understory vegetation. Litter cover was lowest in 2013 (P<0.05) than in any prior year. Cheatgrass and other exotic cover was minimal across all dates and communities, with <1% cover present in plots, except for short-lived increases following 1985 fires in two plots. These findings demonstrate that the removal of livestock resulted in positive changes to critical sagebrush communities, and can inform management decisions where restoration of sagebrush habitat is a priority.