The Forest Service yesterday finalized a plan to reduce the use of chemicals to fight wildfires on national forests, a move designed to protect sensitive species but that some criticized as unscientific.

Forest Service chief Tom Tidwell's record of decision will allow air tankers to continue dropping thousands of gallons of chemical retardants to quell the intensity of wildfires but will limit when they can be used within 300 feet of waterways and require pilots to avoid areas inhabited by vulnerable plants and animals.

The new policy will utilize roughly 12,000 new maps the agency developed with the Fish and Wildlife Service and National Marine Fisheries Service that identifies areas where the chemicals should not be used. Nearly 30 percent of agency lands were included as stream buffers and another 1 percent as sensitive grounds.

The new policy stems from a 2008 lawsuit filed by Forest Service Employees for Environmental Ethics that challenges the agency's environmental assessment of the retardants.

"These new guidelines strike a balance between the need to supplement our boots-on-the-ground approach to fighting wildfires while protecting our waterways and important plant and animal species at the same time," Tidwell said in a statement. "Our new approach will benefit communities, ecosystems and our fire crews."

While the Forest Service has avoided using fire retardants in waterways since 2000, it previously allowed three exceptions for when the chemical could be dropped within 300 feet of streams. The agency will now only allow one exception -- when human life is threatened.

The retardants, which some argue are ineffective at fighting fires, have resulted in massive fish kills and can change the chemical makeup of soil, allowing the invasion of nonnative plant species.

The Forest Service said research shows fire retardants, used since the 1950s, are twice as effective as water at reducing fire intensity. The chemical is intended to quell the spread of fire by cooling and coating fuels and depleting the fire of oxygen, the agency said.

But Andy Stahl, executive director of FSEEE, said the agency has shown no empirical evidence or scientific studies to back its claim.

The retardant, he said, is "a symbolic air show" intended to assuage surrounding communities, most of them in California. While the agency's move is a step in the right direction, it must first demonstrate that the chemical actually works, he said.

"It may be that there are some situations where fire retardants make a positive difference," he said. "But we can't identify them in advance."

Stahl said he was also skeptical of whether the agency's new maps were accurate, particularly in areas the agency has not extensively surveyed.

"The problem is for the terrestrial species," he said. "They only put avoidance zones where they know they exist."

The agency said it will continue to work with manufacturers to develop safer fire retardants.

Its new plan includes procedures for monitoring and reinitiating consultation with FWS and NMFS if fire retardants affect certain species or habitat.