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Impacts of Wild Horses on Riparian Areas in Idaho

The Challenge:

When we hear “eat like a horse,” most of us would think of a lanky teenager with a voracious appetite. Horses require a surprisingly large amount of forage to sustain their hefty body mass. If left unchecked, horses can dramatically impact vegetation, particularly in moisture-limited regions of the West.

Growing concern over damage to rangelands caused by free-roaming or wild horses amid laws that protect them is a contentious challenge. Rural landowners along with agency land managers both face mounting pressure to manage rangelands for multiple values including livestock forage and habitat areas for a suite of wildlife and fish species.

The Bureau of Land Management (BLM) estimates that roughly 49,000 wild horses and burros are currently roaming BLM-managed rangeland in ten western states. With no natural predators, herd sizes can double every four years.

Free-roaming horses are drawn to wet areas—commonly referred to as riparian areas—for water and green forage. Riparian plants stay greener for longer and are more nutritious than the surrounding upland vegetation where plants are not tapping directly into the water table.

Wild horses can drastically impact riparian areas because they have year-round access to streams and meadows, leaving no time for these systems to properly recover from grazing.

Continuous heavy grazing in riparian areas reduces healthy function and balance. Some signs that tell the story of damage from grazing impacts are excessive soil erosion, unstable stream-banks, compacted soils with reduced infiltration, deposits of silt downstream, and overall reduced water quality. Loss of shading also creates drier, hotter conditions for animals that rely on riparian habitats such as fish, birds, deer and elk, livestock, and the horses themselves.

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 these wet areas. We have initiated a study to examine wild horse impacts and use of riparian areas and also compare impacts and use by other types of livestock and wildlife. Our research involves detailed vegetation assessments and game cameras to monitor riparian area use by horses, cattle, and wildlife. Our study areas are located in the Horse Management Areas (HMAs) in Owyhee County and the Challis HMA in Custer County.

Output & Outcomes:

  • Developing a factsheet about wild horse impacts on riparian areas. 
  • Submitting a manuscript for publication to a scientific journal in 2016. 
  • Developing protocols to enhance monitoring use of riparian areas by BLM managers and ranchers. 
  • Sharing information with the BLM to assist with grazing plans and other land uses.

Rangeland Center Members Involved:

  • Karen Launchbaugh - Forest, Rangeland, & Fires Sciences (contact Karen for more information) 
  • Eva Strand - Forest, Rangeland, & Fires Sciences 
  • John Hall – Animal and Veterinary Science and Nancy M. Cummings Research, Extension and Education Center 
  • Sarah Baker – Custer County Extension
  • 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

Contact Us

Mailing Address:
UI Moscow
Natural Resources Bldg.
Room 205
875 Perimeter Dr. MS 1135
Moscow, ID 83844-1135
Phone: 208-885-6536  
Fax: 208-885-6564

Physical and Mailing Address: 
UI Boise
Idaho Water Center
Suite 210 
322 E Front St.
Boise, ID 83702
Phone: 208-364-3176