(CN) - The 9th Circuit on Tuesday ordered the U.S. Forest Service to reassess grazing plans for 48,000 acres in southwest Montana, because the agency based its environmental analysis on the sage grouse, a population that's "virtually non-existent" in the Antelope Basin/Elk Lake area.
The Native Ecosystems Council and two other environmental groups sued the Forest Service in federal court, challenging its decision not to revise the area's environmental assessment or to prepare a new impact statement.
The council argued that the agency refused to take a "hard look" at the impacts its grazing plan would have on local species and their habitats in the Antelope Basin/Elk Lake area of the Beaverhead-Deerlodge National Forest.
The area is mostly open grasslands with mountain sagebrush and some scattered timber along streams.
In assessing the livestock grazing area, the Forest Service used the sagebrush habitat as a proxy for measuring the population of certain "indicator species," including the sage grouse. It then used that data to measure the population of other species that might be affected by grazing in the area.
But this method, called the "proxy-on-proxy" approach, isn't reliable if the management indicator species -- in this case, the sage grouse -- doesn't live in the area, the 9th Circuit ruled.
"There is simply no basis to evaluate the Forest Service's assertion that the sagebrush habitat is sufficient to sustain viable sage grouse when sage grouse cannot be found in the project area," Judge Johnnie Rawlinson wrote.
The court reversed and remanded, saying the Forest Service needs to "fully study the effects of the planned agency action."
In dissent, Chief Judge Alex Kozinski argued that "it is not clear that an indicator species' absence from a particular project area undermines the Service's habitat analysis."
He said the agency need only show that it's "reliably maintaining sagebrush at the levels required for sage grouse."
Kozinski also noted that the majority based its objections on the findings of Dr. John Connelly, "a scientist who has actually endorsed the project."
Connelly wrote the "Guidelines to Manage Sage Grouse Populations and Their Habitats."