Extreme climate fluctuations, such as drought, are likely to increase throughout the 21st century, and this may have strong impacts on the abundance of A. tridentata (Big sagebrush), a critical component of many ecosystems in the western US. Although A. tridentata may be resistant to single year and moderate drought, it may be less resistant to prolonged severe drought. Additionally, disturbance events may exacerbate effects of drought on A. tridentata due to trampling by grazers. In 2019, we established a fully factorial drought x grazing experiment in a sagebrush ecosystem within the Thunder Basin National Grassland (Bill, Wyoming). In this experiment, light, moderate, and heavy grazing treatments were crossed with five levels of rainfall: ambient, -25%, -50%, -75%, and -99%. Within this experiment, we assessed various attributes of sagebrush in these plots to address the following questions: 1) How does A. tridentata populations resist drought treatments? 2) Are A. tridentata individuals more susceptible to drought when combined with grazing? 3) Is the resilience of the herbaceous community linked to the impacts on A. tridentata?
Results/Conclusions
One hundred and five sagebrush individuals were measured within 54 plots (2x2 m each, n=3/treatment). Measurements included: density per patch (numbers of adults and seedlings), height, inflorescence percent, browsing presence, crown volume, and leader growth of adult sagebrush. Additionally, grass species abundance was measured around each shrub individual. As expected, preliminary findings showed that sagebrush growth was negatively impacted along with drought magnitude. However, these effects were exacerbated when combined with intense grazing, likely due to physical damage to plants by trampling. These findings suggest that different types of stress may interact to magnify impacts on plant communities, which may have implications for ecosystem services, such as wildlife habitat. As such, we suggest that understanding the impacts of multiple simultaneous drivers will be critical for informing land management decisions under future climatic scenarios.