Neglect and mismanagement have left western U.S. forests overcrowded, firefighting experts say, leaving them more susceptible to the kinds of major wildfires that are currently ravaging California.

California state and federal officials have responded to about 4,500 fires this year that have burned nearly 400,000 acres of land, easily outpacing last year’s record burns.

Fires are bigger and lasting longer in part due to hotter and drier weather that most experts say is caused by climate change. But overcrowding has also made the fires more intense: The Department of Agriculture reported in December that about 27 million trees had died statewide on federal, state, and private lands since November 2016.

“Our forests are dramatically overcrowded,” said Krystal Beckham of the Little Hoover Commission, an independent California oversight agency that has called for major changes in the state’s forest management practices.

“There are some places where there may be four times as many trees as there should be,” Beckham said. “When you have trees that close together, they can’t get the water they need, so they are more susceptible to drought, insects, and disease. And when they start dying, they become a terrible fire threat.”

There are two major ways to prevent fires from starting, experts say. The first is for officials to intentionally set fires to take away ignitable material like brush off the forest floor and give trees more space to breathe.

The other method, called forest thinning, involves crews removing small trees to reduce the amount of fuel in dry forests.

But these activities are expensive. And the U.S. currently faces a backlog of needed forest management projects, as federal and state agencies have used more of their budgets responding to wildfires, rather than preventing them.

“Since both the state and federal agencies have been devoting greater and greater resources to suppression to fight the immediate problem, the trickle down of that is less money for strategies on how to get in front of the fire problem,” said John Barnell, the acting CEO and director of the Society of American Foresters.

The Forest Service for years has taken money from other preventative accounts to make up for shortfalls in firefighting funding.

This past March, as part of the omnibus government spending bill, Congress addressed the “fire borrowing” problem by establishing a contingency account for use in bad fire years, funded with more than $2 billion a year through 2027.

The bill also allowed the Forest Service to do more prescribed burns or forest thinning with less rigorous environmental reviews.

But conservatives say that those changes are not enough, and want to enact further reforms in the upcoming farm bill to make it easier for states and counties to assist in managing federal forests, and to combat lawsuits by environmentalists that they say slow down projects.

“We’ve yet to see the worst of forest fires. The climate is drier and warmer, and that leads to more fires,” said Rep. Bruce Westerman, R-Ark., a licensed forester. “But the forest doesn’t stop growing, and the trees don’t start crowding each other. Until we realize that, we will continue seeing the devastation we are seeing right now.”

The federal government has only so much power in fighting and preventing fires.

Of the dozen or so wildfires currently burning in California, National Interagency Fire Center spokeswoman Jessica Gardetto said, only five are on Forest Service land. Others are on state or private land, or a mix of jurisdictions.

California state officials maintain that they’re taking prevention seriously.

The California Legislature provided more than $200 million this fiscal year for forest management, said Scott McLean, the information officer for Cal Fire.

Last year, Cal Fire chief director Ken Pimlott partially blamed mismanaged forests for wildfires in October that killed more than 40 people in Northern California, the state’s deadliest wildfire event on record.

“The fires are extremely dynamic this year, they are very aggressive, and they are killing people,” McLean said, noting that eight civilians and four firefighters have died from wildfires in California this year. “Fire prevention has always been very important, and the good news is the last couple of years we have become more aggressive with that.”