How do you maintain 158,000 miles of trails on a shoestring budget? Ask for volunteers.

The U.S. Forest Service manages more miles of trails than any other government agency. But with firefighting consuming an ever-growing share of the budget, agency officials are scrambling to find sufficient funds to maintain those trails. More than half of the agency’s budget now goes to wildfire suppression.

Forest Service officials say only about a quarter of its trails are maintained to the agency’s standards.

Last year, Congress passed the National Forest System Trails Stewardship Act, which calls for doubling the amount of trail work undertaken by volunteers by 2021. Forest Service officials are asking the public to submit proposals for trail maintenance in each of the agency’s nine regions. The agency is soliciting public input through April 15.

Joe Meade, the agency’s director of recreation programs, said the Forest Service chief will have ultimate say in which projects get the go-ahead.

“This is a pretty unique opportunity, to have Congress emphasize how important this trail system is,” Meade said. “Our interest is to move as efficiently and effectively as we can.”

The legislation calls for the agency to identify at least one “priority area” for trail maintenance in each of the nine regions it administers. The Forest Service can establish as many as 15 such areas.

Volunteers contributed about 1.4 million hours of work in 2015, according to the Forest Service, improving nearly 30,000 miles of trails.

A 2013 study by the General Accountability Office found that the Forest Service had a $314 million backlog of trail maintenance. In recent years, the agency has spent about $80 million annually on trail maintenance.

The trails stewardship act also calls for using fire crews to work on trails when they are available. It also requires the Forest Service to establish a pilot program that would allow outfitters and guides to offset all or part of the fees they pay for using national forests by undertaking trail maintenance work.

Last week, the Trump administration released a budget blueprint that would slash funding for the Department of Agriculture, which oversees the Forest Service, by 21 percent. The proposal calls for the Forest Service to maintain current funding levels for firefighting, meaning the agency may face deep cuts in other areas.

“We’re looking for ways to turn over every stone to enhance our trail system,” Meade said.