Ecological Effects of Free-Roaming Horses in North American Rangelands

Free-roaming horses are a widespread conservation challenge. Horse use (grazing and related impacts) is largely unmanaged, leading to concerns about its impact on native plant communities and ecosystem function. We synthesized the literature to determine the ecological effects of free-roaming horses in North American rangelands. Largely unmanaged horse use can alter plant community composition, diversity, and structure and can increase bare ground and erosion potential. Free-roaming-horse use has also been linked to negative impacts on native fauna. Horses have repeatedly been shown to limit and even exclude native wildlife's use of water sources. These effects would likely be greatly reduced if the horse populations were better managed, but sociopolitical factors often preclude improved management. Using rigorous ecological research to educate politicians and the general public may facilitate the development of science-based management of free-roaming horses; however, ecological effects may have to become more severe before such changes can be realized.