BILLINGS, Montana (AP) — The Biden administration is moving to conserve groves of old-growth trees on federal land by revising management plans for national forests and grasslands across the United States as climate change amplifies the threats they face from wildfires, insects and disease.

Agriculture Secretary Tom Vilsack said the goal was to provide an “ecologically-driven” approach to older forests — an arena where logging interests have historically predominated. It would be the first nationwide amendment to US Forest Service management plans in the agency’s 118-year history, he said.

Details were obtained by The Associated Press in advance of Tuesday’s public release of the proposal.

It follows longstanding calls from environmentalists to preserve older forests that offer crucial wildlife habitat and other environmental benefits. The timber industry has fought against logging restrictions on government-owned lands.

President Joseph Biden’s administration appears to be aiming for a middle ground: It would sharply limit commercial timber harvests in old growth forests while allowing logging to continue on “mature forests” that have not yet reached old growth stage.

“This creates a commitment to resiliency, a commitment to restore and protect the existing old growth that we have from the threats that we see,” Vilsack said in an interview.

Old growth forests, such as the storied giant sequoia stands of northern California, have layer upon layer of undisturbed trees and vegetation.

There’s wide consensus on the importance of preserving the oldest and largest trees — both symbolically as marvels of nature, and more practically because their trunks and branches store large amounts of carbon that can be released when forests burn, adding to climate change.

Underlining the urgency of the issue are wildfires in California that killed thousands of giant sequoias in recent years. The towering giants are concentrated in about 70 groves scattered along the western side of the Sierra Nevada range.

“This is a step in the right direction,” said Chris Wood, president of Trout Unlimited and a former Forest Service policy chief. “This is the first time the Forest Service has said it’s national policy will be to protect old growth.”

Yet experts say there’s no simple formula to determine what’s old. Growth rates among different tree types vary greatly — and even within species, depending on their access to water and sunlight and soil conditions.

Groves of aspen can mature within a half century. For Douglas fir stands, it could take 100 years. Wildfire frequency also factors in: Ponderosa pine forests are adapted to withstand blazes as often as once a decade, compared to lodgepole pine stands that might burn every few hundred years.

The results earlier this year from the government’s first-ever national inventory of mature and old-growth forests on federal land revealed more expanses of older trees than outside researchers had recently estimated. The Forest Service and federal Bureau of Land Management combined oversee more than 50,000 square miles (129,000 square kilometres) of old growth forests and about 125,000 square miles (324,000 square kilometres) of mature forests, according to the inventory.

Most are in Western states such as Idaho, California, Montana and Oregon. They’re also in New England, around the Great Lakes and in Southern states such as Arkansas, Kentucky and West Virginia, according to the Forest Service.

But representatives of the timber industry and some members of Congress have been skeptical about Biden’s ambitions to protect older forests, which the Democrat launched in 2021 on Earth Day. They’ve urged the administration to instead concentrate on lessening wildfire dangers by thinning stands of trees where decades of fire suppression have allowed undergrowth to flourish, which can be a recipe for disaster when fires ignite.

“Let’s be real about who the groups asking for this are: They have always opposed commercial timber harvests on the national forest system,” said Bill Imbergamo with the Federal Forest Resource Coalition, a timber industry group. “Is that the correct emphasis right now when most of the old growth losses are coming from insects, fire and climate change stressors working in tandem?”

The proposal to revise management plans for 128 national forests and national grasslands is expected to be completed by early 2025. However, it’s uncertain if the change would survive if Biden loses his 2024 re-election bid.