The ruling might affect a hotly contested thinning project on the North Kaibab Plateau, which is opposed by environmental groups because it includes large-diameter trees.

The 9th Circuit Court of Appeals ruled in favor of environmental groups -- the Center for Biological Diversity and the Sierra Club -- in their lawsuit against the U.S. Forest Service. The suit contended that the agency failed to protect the northern goshawk in national forests within Arizona and New Mexico.

The unanimous opinion, written by Judge Donald Pogue, agreed with the Center and the Sierra Club that the Forest Service did not consider or disclose to the public scientific evidence that the goshawk prefers old-growth and mature forest for breeding and foraging in its development of a regional goshawk management plan.

"The (Forest) Service's failure to disclose and analyze these opposing viewpoints violates NEPA," the court wrote in its ruling, referring to the National Environmental Policy Act that guides environmental studies.

"The applicable regulations require the (Forest) Service to disclose and discuss the responsible opposing views in the final impact statement," the court wrote in its ruling.

The Forest Service has, for the past decade, labeled the goshawk as a "habitat generalist," which means it does not necessarily need old-growth trees or large trees. But environmentalists have pointed to studies that show the goshawk consistently nests and forages in closed-canopy, old-growth forests.

Information in the suit shows that the U.S. Fish and Wildlife Service and the Arizona Game and Fish support those findings.

Goshawks are not endangered, but they are an indicator species used to assess the health of a forest.

The Center filed a suit to get the goshawk listed as a threatened species, but the Court of Appeals ruled against the environmental group in that case earlier this year.

Although the goshawk guideline ruling affects the entire Southwest, the North Kaibab has the greatest concentration of goshawks, according to Brian Segee of the Center for Biological Diversity.

"It's been about a decade-long battle over these guidelines, and at the very core of this ruling, with the guideline, is that it has brought (into question) continued logging of old-growth and ponderosa pines," Segee said.

Still, neither Segee nor officials with the Forest Service know specifically what impacts the Court of Appeals ruling will have.

"The first step is to figure out what the order means," said Pat Jackson, director of appeals and litigation for the Forest Service regional office in Albuquerque. "All I can tell you is that the court has found a procedural problem as it relates to the bird being a habitat generalist or specialist. We will be working with Department of Justice to figure out what we need to do."

Jackson also is unsure of how the ruling will affect a timbering project on the East Rim of the North Kaibab, which the Center, along with the Southwest Forest Alliance, opposes because the project called for the removal of old-growth trees.

The goshawk guidelines used by the Forest Service allow for the cutting of some 18- to 24-inch trees to help open up parts of the forest to allow for the goshawk's prey to thrive. The project calls for about 7,000 of these trees to be cut on 7,000 acres, or an average of one per acre. It will not reduce the percentage of Kaibab National Forest classified as old-growth, which will remain at about 20 percent.

But the Forest Alliance contends that all the large trees should remain to promote a healthy forest, as they often are fire-adapted.

Roxanne George of the Forest Alliance said that the recent ruling should help the environmental groups in their efforts to stop the East Rim project, since the project is based on a management plan that includes the goshawk guidelines.

In October, their appeal on the project to the regional Forest Service office was denied.

"We are in discussion of further challenging" the timber project, George said. "This ruling from the Court of Appeals shows the East Rim timber sale is not valid."

The timber project also includes the removal of 400 extra-large trees, more than 24 inches in diameter, out of a total of 267,000 trees removed. The Forest Service reports they are targeted because they have a mistletoe infestation, which stunts the tree's growth and development.