Nevada removed feral horses and burros from Sheldon National Wildlife Refuge; some streamside and upland vegetation gradually recovered

If your social media feed has ever featured a viral video of mustangs galloping across the American West, you're aware of the symbolism of wild horses: freedom, determination, the rugged frontier spirit. It's therefore somewhat surprising to learn that a major conservation success story for the Great Basin region of the last decade involved removing thousands of horses and burros from a public land refuge.

The subject of this scientific discussion is the Sheldon National Wildlife Refuge, a 575,000-acre tract of high desert in northwest Nevada. According to a 2012 federal assessment conducted by the US Fish and Wildlife Service, 44 percent of the refuge's streams and 80 percent of its springs had been "severely degraded" by feral horses and burros by the year 2002, animals that are not native to the area and that originated from ranch stock that were either set free or left behind decades earlier.

The issue that no one had posted about


Horses and burros don't tend to graze in the same patterns that native wildlife would; they congregate more around water sources and inflict more damage on streambanks, and cause more soil compaction, than pronghorn or sage grouse would naturally. Domestic cattle grazing had ceased in the Sheldon refuge by the early 1990s, which gave researchers an unusually clear opportunity, rare in rangeland ecology, to isolate horse-specific impacts, though even here scientists still relied on fenced exclosure plots to separate the effects of horses from the legacy of decades of earlier livestock use. Wildlife managers began targeted population controls not long after, including a 2008–2011 sterilization program, before a 2012 management plan set a formal timeline for removing all feral horses and burros; major roundups followed in 2013 and 2014, with most of the animals placed in adoption programs rather than killed. The refuge reported by the mid-2010s that it had removed nearly all of the feral horses and burros that had once roamed the area.

What the research actually says

This is where it becomes interesting for people who assume that “fewer large grazers equals healthier land” is simply common sense. It mostly is, but the recovery was not immediate or universal. Researchers with the USDA Agricultural Research Service used exclosure plots on and around Sheldon, starting in 2008, to directly compare horse-excluded and horse-grazed ground. Their 2012 findings, titled “Impacts of Feral Horse Use on Rangelands and Riparian Areas,” showed that upland rangeland vegetation saw only minor improvements when horses were excluded, and perennial grasses saw only slow progress. Vegetation in riparian zones, or along the edges of creeks and springs, was far more dramatically impacted, with bare ground making up only a third of that seen before horse-exclusion measures.

A separate, frequently-cited and peer-reviewed 2007 study titled “Multi-scale responses of vegetation to removal of horse grazing from Great Basin (USA) mountain ranges,” published in the journal Plant Ecology by Erik Beever, Robin Tausch and Wayne Thogmartin, examined sites in nine different mountain ranges elsewhere in the Great Basin (not Sheldon), comparing ground still grazed by horses to ground where horses had already been absent for 10 to 14 years at the time of the study’s 1997–98 field surveys. It found that horse-free areas had up to nearly double the amount of shrub cover, significantly more plant species, and almost triple the coverage of native grass compared to areas that continued to allow feral grazing. Because that horse-free baseline dates back to the mid-1980s, long before Sheldon’s own removal campaign got underway, the study can’t be read as a direct progress report on Sheldon. It’s better understood as independent evidence from elsewhere in the region that horse removal, given sufficient time, can have a noticeable impact on the plant community of a given area.

Why this debate continues

None of this has made the issue easy, however. Advocates for wild horses have argued that mass removals are inhumane, or that horses are unfairly blamed for damage caused by years of other land use. Wildlife agencies have maintained that an ecosystem not evolved to deal with large-scale herbivory as intense as horses and burros can only tolerate so much before native species begin to be competitively excluded, particularly in the face of drought and wildfire pressures. Both sides are correct within their own reasoning, but rarely does either have the opportunity to advance their arguments beyond knee-jerk reactions that would appeal more to emotion than hard science.

What the Sheldon refuge data does represent is a rare chance for conservationists to have a clear before-and-after scenario with actual statistics to back it up. Perhaps the most important lesson is this: while wild horses are not the only factor, wildlife populations can exceed what a shared ecosystem can support, and large-scale changes often take time to appear.