(AP) — The Forest Service has spent more than $2 billion battling forest fires around the country — a record as wildfires blacken the American West in one of the nation’s worst fire seasons.

Wildfires have ravaged the West this summer with 64 large fires burning across 10 states as of Thursday, including 21 fires in Montana and 18 in Oregon. In all, 48,607 wildfires have burned nearly 13,000 square miles (33,586 square kilometers).

The fires have stretched firefighting resources, destroyed more than 500 homes and triggered health alerts as choking smoke drifted into major Western cities.

The Forest Service, part of the U.S. Department of Agriculture, is the nation’s primary firefighting agency.

Agriculture Secretary Sonny Perdue said the severe fire season means officials “end up having to hoard all of the money that is intended for fire prevention, because we’re afraid we’re going to need it to actually fight fires.”

The emphasis on firefighting means that money for prescribed burns, insect control and other prevention efforts is diverted to putting out fires in what Perdue called a self-defeating cycle. The end result is that small trees and vegetation remain in the forest for future fires to feed on.

“That’s wrong, and that’s no way to manage the Forest Service,” Perdue said.

The Agriculture Department has been asking Congress for years to change the way firefighting is funded so the Forest Service does not have to raid non-fire programs in bad years.

The spending figure announced Thursday marks the first time wildfire spending by the Forest Service has topped $2 billion. The previous record was $1.7 billion in 2015.

The figures do not include spending by Interior Department agencies such as the Bureau of Land Management and National Park Service, nor do they include spending by state and local governments.

The Interior Department says it has spent at least $391 million with several weeks left in the fire season. The previous record for combined federal firefighting costs was $2.1 billion in 2015.

Some previous years have had bigger areas burn but lower costs to fight fires.

“The level of continuous activity and the length of the fire season is driving our costs,” Forest Service spokeswoman Babete Anderson said.

Parts of the West have suffered through above-average fires for months, she said.

This year’s fires have renewed discussions about thinning overgrown forests to reduce the risk.

Forest fuels are at “powder keg levels,” said Paul Hessburg Sr., a Forest Service research landscape ecologist.

Interior Secretary Ryan Zinke on Tuesday directed land managers and park superintendents in his department to be more aggressive in cutting down small trees and underbrush.