Effects of feral horse herds on plant communities across a precipitation gradient

Western North American Naturalist
By: , and 



Feral horses are widespread in the western United States, with the majority of feral horse herds found in the Great Basin. There is a federal mandate to manage these herds in order to maintain “ecological balance”; however, understanding of the specific effects of feral horse grazing on rangeland plant communities in this region is incomplete. To address this research gap, we utilized long-term grazing exclosures and fenceline contrasts to evaluate the impacts of feral horses on several plant community variables (diversity, richness, dominance, and biomass) and species composition. Because the effects of grazing can vary with site precipitation and productivity, we selected 5 sites from 4 different rangeland types (Great Basin Desert, Colorado Plateau, Rocky Mountain grassland, and mixed grass prairie) that spanned a mean annual precipitation gradient of 229 to 413 mm. Our results did not reveal a significant effect of feral horse grazing on plant community composition, species richness, diversity, evenness, or dominance. In contrast, total aboveground herbaceous biomass and grass biomass were significantly reduced with feral horse grazing, but these effects did not vary with mean annual precipitation. Our results suggest that, at least at the sites we studied, feral horses have affected the plant community by reducing herbaceous biomass but have not caused plant community shifts. Additional multisite studies, preferably with standardized exclosures and larger sample sizes, would increase our understanding of feral horse grazing effects and inform management of feral horse herds in the western United States.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Effects of feral horse herds on plant communities across a precipitation gradient
Series title Western North American Naturalist
DOI 10.3398/064.077.0412
Volume 77
Issue 4
Year Published 2018
Language English
Publisher BioOne
Contributing office(s) Fort Collins Science Center
Description 14 p.
First page 526
Last page 539
Country United States
State Colorado, Montana, Nevada, North Dakota, Utah
Other Geospatial Clan Alpine Herd Management Area, Pryor Mountain Wild Horse Range, Spring Creek Basin Herd Management Area, Sulphur Herd Management Area, Theodore Roosevelt National Park
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