GRANTS PASS, Ore. — A federal judge has upheld a requirement that Northwest national forests look for hundreds of hard-to-find but ecologically important species like snails, mushrooms and mosses before cutting down big trees.

The ruling Thursday from U.S. District Court in Seattle effectively strikes down the last surviving piece of the Bush administration’s strategy to boost logging in spotted owl territory.

Judge John C. Coughenour did not immediately reinstate the so-called survey and manage rule. He wants to hear more from the government and conservation groups before issuing an order.

But he said in his ruling that the U.S. Forest Service failed to show that the rule was doing anything but what it was intended to do — protect the small but essential pieces that make an ecosystem work.

“The standard protects only truly rare and uncommon species, which as the court notes, are the ‘little things that run the world,’ ” said Pete Frost, attorney for the Western Environmental Law Center, which brought the lawsuit on behalf of conservation groups. “These species allow healthy forests to function, because they do things like conserve water, filter sediment and provide food.”

Survey and manage was part of the Northwest Forest Plan, adopted by the U.S. Forest Service, U.S. Bureau of Land Management and U.S. Fish and Wildlife Service in 1994 to lift a federal court order banning old-growth logging on national forests in Washington, Oregon and Northern California to protect habitat for the northern spotted owl and salmon, both threatened species.

The plan reduced timber harvests about 90 percent, and when the Bush administration took office in 2000, it began dismantling environmental protections in the plan. But federal judges kept reinstating them, and timber harvests remain a fraction of their peak in the 1980s.

The Bush administration dropped the survey and manage rule in 2004, a judge restored it, and the rule was dropped again in 2007.

Ann Forest Burns, vice president of the American Forest Resource Council, a timber industry group, said they were not happy with the ruling, and felt it would make it more difficult for the Forest Service to thin overcrowded stands to reduce the threat of wildfire.

Burns said the one “glimmer of goodness” in the ruling was that the judge found the agencies did not violate environmental laws in their consideration of the effects of global warming on old-growth forests.

Forest Service spokesman Tom Knappenberger said they had not seen the ruling, so could not comment on it.