Project Number: 2070-21630-002-08-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2017
End Date: Aug 31, 2020
Concerns of a potential listing of sage-grouse under provisions of the Endangered Species Act are driving land management decisions and impacting rangeland agriculture in most western states. Grazing has been identified as an important factor impacting sage-grouse nesting habitat; however, while the effects of livestock grazing have been previously articulated via peer review science, there has been no effort to determine the impacts of feral horse grazing. Given that feral horse numbers are at an all-time high nationally, and that horse density in most publically-managed Herd Management Areas is above the Allowable Management Level, quantifying the impacts of feral horses on sage-grouse habitat is of critical importance. Research associated with these outgoing funds will provide baseline information on the effects of free-ranging horses on habitats used by sage-grouse for nesting purposes.
This study will take place on private lands in southeast Oregon using privately-owned horses. Five acre subplots within fenced ten acre plots (five plots total) will be managed under growing season horse grazing and initially stocked at levels that reflect current average stock density on federal lands. The remaining subplot within each plot will not be grazed. Location of plots will be within areas currently used by radio-marked sage-grouse hens as nesting habitat. In each of two growing seasons, percent pasture utilization, utilization of understory and interspace perennial bunchgrass plants, and structural habitat characteristics (horizontal foliar obscurity, shrub morphology, functional plant group cover, and shrub/grass height) will be monitored in all subplots (grazed and ungrazed) on a weekly basis until pasture utilization in grazed plots reaches 75%. Logistic regression will be used to evaluate probability of grazing on perennial bunchgrasses as a function of location (interspace vs. under canopy) and percent pasture utilization in grazed subplots. Multiple regression will be used to evaluate relationships between increasing levels of horse utilization over time and changes in structural habitat characteristics. The latter analysis will compare rates of change over time in both grazed and ungrazed subplots.