Wild horse advocates claim the federal government has underestimated the amount of winter range available to a herd in Oregon’s Ochoco National Forest.

The underestimate has caused the U.S. Forest Service to set an “artificially low” limit on the Big Summit Territory’s wild horse population, according to the Central Oregon Wild Horse Coalition.

The debate over wild horse management is a longstanding controversy in the West, with ranchers claiming their cattle are blamed for rangeland damage caused by horses.

Meanwhile, wild horse advocates claim that federal agencies have restricted herd sizes on public lands to allow for more grazing by livestock, even though federal law is meant to protect wild horses.

What plaintiffs want

The Central Oregon Wild Horse Coalition has asked the 9th U.S. Circuit Court of Appeals to overturn the agency’s “appropriate management level” of 47-57 horses for the Big Summit Territory, which would require reducing the current herd’s size by about two-thirds.

The Forest Service estimated that only 19% of the 5,000-acre territory was available as winter range, ignoring data that horses have additional areas available to them for forage, said Sasha Petrova, the plaintiff’s attorney.

The agency’s appropriate management level, or AML, for the territory is “arbitrary and capricious” in violation of federal laws governing wild horses and environmental policy, according to the coalition.

“By committing itself to recalculating this AML, the agency is committing itself to following the law,” Petrova said during oral arguments Dec. 2 in San Francisco.

The Forest Service countered that it had thoroughly considered all the data provided by the public in setting the AML but “reasonably declined” to rely on a map of winter range provided by the coalition.

Setting the appropriate level for the herd’s size involves technical decisions that are firmly within the agency’s discretion, said Robert Stockman, attorney for the government.

“The agency did a lot of work here to get it right,” Stockman said.

The current level of horses in the territory has contributed to a “decline in riparian conditions,” which was documented with “various scientific methods” by the Forest Service, according to the agency’s court brief. “The Service reasonably developed an AML to achieve a thriving natural ecological balance and exercised its discretion to decide which methodology, surveys, and scientific information to rely on.”

Contrary to the plaintiff’s claims, the Forest Service adequately considered the AML’s effect on the herd’s genetics, the agency said. For example, the agency plans to introduce new mares to the herd to ensure genetic diversity.

“The herd will be healthier genetically in light of the new herd management plan,” Stockman said.