2014-2018: Impacts of Wild Horses on Riparian Areas in Idaho

The Challenge:

Riparian areas comprise just 2 percent of western lands, but they are considered some of the most ecologically important habitats because they provide critical resources such as forage, cover and water for wild and domestic animals. But continuous heavy grazing by wild horses, livestock and wildlife can damage riparian plants and lead to unstable streambanks and reduced water quality. Loss of shading along streams can also create drier, hotter conditions for animals that rely on riparian habitats.

Wild horses, livestock and wildlife are all drawn to riparian areas for water and green forage. Studies have shown that grazing by livestock and wild horses can damage these areas. Wild horses require surprisingly large amounts of forage to sustain their hefty body mass (hence the familiar phrase “eat like a horse”) and they also have year-round access to streams and meadows, leaving no time for these systems to properly recover from grazing.

Wild horses roam public lands in 10 western states. With few natural predators, their population can increase by 15-20 percent each year and double every four years. This fast-paced growth can exceed the management levels set within herd management areas (HMAs), and can contribute to ecological damage.

If left unchecked, wild horses can dramatically impact rangeland plant communities. Of particular concern, and what our study addressed, is the effect wild horses might have on riparian areas along streams, creeks, and springs in the West.

Our Response:

While many published works document the impacts of cattle grazing on riparian health, few studies examine the impacts of free-roaming horses, specifically in riparian zones. We compared intensity of use by wild horses, cattle and wildlife in riparian areas. Our research involved detailed vegetation assessments and game cameras to monitor riparian area use by horses, cattle and wildlife. Our study areas were located in HMAs in Owyhee County, Idaho and the Challis HMA in Custer County, Idaho.

Findings:

Our analysis showed that both wild horses and cattle damage riparian ecosystems if not properly managed. Interestingly, the use of a specific riparian area by one species (cattle, horses or wildlife) did not cause another species to avoid the area. In fact, we found a positive relationship among species, meaning that livestock, wild horses and wildlife were probably attracted to riparian areas for similar reasons and that the presence of another species was inconsequential.

When looking at effects of intensity of use, our study shows that an individual horse can have a greater effect on riparian attributes such as streambank disturbance, vegetation height and plant biomass than and individual cow (though both species can alter riparian plant communities and stream banks).

It is well known that effective management of riparian areas can be accomplished by controlling season of grazing and levels of use. Riparian management is difficult in areas with wild horses because these animals generally have year-long access to riparian areas, and levels of use or population levels are difficult to restrict. The tough management reality is that in areas with both wild horses and cattle grazing, land managers and ranchers need to account for potential additive effects.

Output and Outcomes:

Read and download this publication: Impacts of Wild Horses, Cattle, and Wildlife on Riparian Areas in Idaho. April 2018. Rangelands. 40(2):8 pages

Rangeland Center Members Involved:

• Karen Launchbaugh — Forest, Rangeland and Fires Sciences (contact Karen for more information) 
• Eva Strand — Forest, Rangeland and Fires Sciences 
• John Hall — Animal and Veterinary Science and Nancy M. Cummings Research, Extension and Education Center 
• Sarah Baker — UI Extension, Custer County     
• Molly Kaweck — Graduate Student

Partners & Sponsors:

• BLM Wild Horse and Burro Program in Idaho 
• Mountain Springs Ranch 
• Idaho Rangeland Resource Commission 
• University of Idaho Berklund Research Assistantship 
• University of Idaho David Little Endowment 
• USDA-ARS Northwest Watershed Research Center