Publication Date
8-2024
Date of Final Oral Examination (Defense)
6-18-2024
Type of Culminating Activity
Thesis
Degree Title
Master of Science in Biology
Department Filter
Biology
Department
Biology
Supervisory Committee Chair
Kelly Hopping, Ph.D.
Supervisory Committee Member
Marie-Anne de Graaff, Ph.D.
Supervisory Committee Member
April Hulet, Ph.D.
Supervisory Committee Member
Allison Simler-Williamson, Ph.D.
Abstract
Cheatgrass (Bromus tectorum) invasion is widespread across the Great Basin region of the United States and is expected to continue. Cheatgrass degrades ecosystem functioning, increases the risk of wildfire, and negatively affects rangeland-based agriculture and other land uses. Targeted grazing—the use of livestock to accomplish a vegetation management objective—has been suggested as a management practice that could combat cheatgrass invasion at the landscape level. However, knowledge of targeted grazing at a management-relevant scale and its effects on other vital ecosystem components, such as non-target plant species and soil properties, remains limited. To test the efficacy of sheep targeted grazing to cheatgrass management and its effects on other ecosystem components, I collaborated with researchers, U.S. Forest Service staff, and ranchers to establish a targeted grazing experiment in the Sawtooth National Forest, Idaho. The experiment consists of five treatments: higher intensity targeted grazing in (1) spring, (2) fall, and (3) spring + fall when cheatgrass is green; (4) low-intensity summer grazing that is the norm for this region; and (5) no grazing, which represents a grazing exclusion scenario. I used generalized linear mixed effects models to assess vegetation and soil responses from the experiment’s before-after control-impact design. I found that after one year of grazing treatments, spring targeted grazing significantly decreased cheatgrass cover by 14.43 % ( 0.42 %), but also decreased non-target forbs and other graminoids by 36.1 % ( 1.58 %) and 11.1 % ( 0.92 %), respectively. Total soil organic matter, carbon, and nitrogen concentrations did not change with grazing treatment. In contrast, mineral nitrogen concentrations increased with spring targeted grazing, which, while not a statistically significant effect, could have ecologically relevant, longer-term feedbacks to aboveground vegetation. While these results are promising as an early indicator of targeted grazing’s ability to reduce cheatgrass and associated risks, they also highlight that need for management practices to consider non-target plants and changes to soil nitrogen. Additional years of grazing treatments and data collection are ongoing and will be needed to better understand the potential of sheep grazing as a long-term cheatgrass management tool.
DOI
https://doi.org/10.18122/td.2276.boisestate
Recommended Citation
Sorrentino, Madelyn, "Ecosystem Effects of Targeted Grazing with Sheep to Manage Cheatgrass" (2024). Boise State University Theses and Dissertations. 2276.
https://doi.org/10.18122/td.2276.boisestate