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Dead trees are fueling California wildfires, but what's killing the trees?

The devastating October 2017 wildfires in Northern California were the worst in the state’s history, and fire scientists expect more of these extreme blazes to become the norm. Millions of dead trees turn forests into tinderboxes. And many of those trees were killed by one tiny culprit — the bark beetle.

These native pests chew their way through evergreens, sometimes cutting through 100,000 trees in a day.There are currently more than 100 million dead trees in the state, waiting to fall or burn. And while official policy is to clear and sell the dead trees, some ecologists question that logic. 

Bugs and Rot

If you need help finding dead trees and bark beetles, Tom Smith is your guy. He works for the California Department of Forestry and Fire Protection, identifying and managing tree diseases and pests. He calls himself a "bugs and rot" man.

Smith says if you want to find bugs and rot close to the Bay Area, head up to Mount Diablo, in Contra Costa County. So we meet there, in a parking lot at the base of the mountain. He points up a steep hill to a green pine forest blemished by brown, dying trees.

“Those are evergreen trees,” Smith says. “When they're brown like this they are dead, they're not coming back.”

Smith grabs his pocket knife and we hike up the hill.

“What we’ve got here is actually the northernmost stand of Coulter pine in California, and it's getting really walloped by what are called ips engraver beetles.”

Credit Angela Johnston
Dead trees on Mount Diablo.

Ips engravers are just one of many species of bark beetles. The big one in California is called the western Pine beetle; that’s the kind Smith believes has killed around 100 million pine trees.


66 million dead trees

Smith says that estimate is on the low side. The dying ones out here on Mount Diablo probably weren’t counted when the state did a fly-over survey last October. Usually, one percent of trees die each year, due to insects, disease, overcrowding or fire. Right now, Smith says we’re dealing with annual mortality rates in the 20-80 percent range. Climate change and the recent drought have made the trees weaker.

“The bark beetles really like trees that are under stress, and the drought puts the trees under stress,” Smith says.

We eventually reach a group of small pine trees. The needles on some of them are green; others have a singed look. Their branches droop, and some have no leaves at all.

Credit Angela Johnston
Bark beetles leave a pattern on the inside of the tree. It's called a gallery.

“In fact, we might be able to see some beetles on them — they're feeding right under the bark,” Smith says. “Most of them are about the size of a grain of rice or smaller, blackish in color — pretty nondescript-looking unless you know what you’re looking for. But they're attacking it by the thousands.”

Bark beetles can fly up to two miles to find a tree to attack. Once they find one, they bore their way inside. If the beetle is successful, it releases pheromones that tell other beetles to come on over. Inside the tree, the beetles eat the inner layer of bark.

“And they'll girdle the tree so no water and nutrients are moving up and down the tree anymore,” Smith says, pointing to a tree that’s on its way out.

If you look closely at the bark, you can see tiny holes where the beetles have bored through. Smith cuts into one of the trees with his pocket knife. Trees that have been attacked by bark beetles have squiggly carvings inside the bark called galleries.


They’re strangely beautiful, even though it means they’re a sign of the tree's impending death.


Fire hazard

Smith can’t tell me how many trees on Mount Diablo are infested with bark beetles. But he does say it’s nothing compared to how many trees are dying in the Southern Sierra Nevada — almost 80 percent.


And right now the dead trees are a major fire hazard.

"One of the concerns is that if people cut trees instead of letting the beetles kill the trees, in the long run that may actually interfere with the ability of these forests and these pine species to adapt to the future of climate change." —Eric Biber, UC Berkeley

“They're around all these communities and they’re just going to sit there and be more fuel that can burn in more fires, more huge fires in the future. So I’m really concerned [about] what we’re going to do with all this material, and I don’t have answers right now,” Smith says.

State of emergency

That’s where the state comes in.


In fall 2015, Governor Jerry Brown issued an emergency proclamation urging city, regional and state agencies to bypass environmental regulations to cut down trees — ones that have already burned and also ones that are losing the bark beetle battle and in danger of burning later.


But saw mills around the state have been completely full, and there aren’t enough bio-energy facilities to turn 100 million dead trees into fuel. So, the state is looking to create new markets for dead California trees. And you don’t have to look further than Lake County — two hours north of San Francisco — to see this happening.


On Cobb Mountain in Lake County, the land still bears the scars from last fall’s ferocious Valley Fire. Most of the hills are charred black.  


There are patches of green forest here and there, where a sudden change in wind steered the flames in a different direction.


But these green, surviving trees may not be here for much longer, because bark beetles are killing most of what is left across the county.


Danny Prather is a fifth-generation timber operator. Basically, that means he has a permit to cut down trees. This year, he says more than half the trees he’s cutting down are ones that have already been infested by beetles.

“Even with that, and removing the ones with active beetles still in it, they still come back and spread,” Prather says.

Today, he’s cutting down, or felling, a few ponderosa pine trees to thin out the forest near his house. A sparser group of trees makes it harder for bark beetles to move from tree to tree.

Prather says mills in California don’t want to buy pine; it’s not as valuable as redwood or cedar. And because the local mills are all full, he — along with the rest of the state — has to find other markets for the wood.

This tree, and the dozens of others he’ll fell this year will get put on a truck bed, transported to the port of Richmond, put on a boat and shipped to China.


Prather will make just enough money to break even.


“They're paying more than our own mills, which I don’t know how that can work out financially; but more importantly it gets our dead wood out of the forest, which is a good thing,” says Prather.

Letting the beetles take control


Clearing trees that are already dead is a good thing for preventing fires. But some experts think we shouldn’t be so quick to cut the green ones down and ship them away.


“One of the concerns is that if people cut trees instead of letting the beetles kill the trees, in the long run that may actually interfere with the ability of these forests and these pine species to adapt to the future of climate change,” says U.C. Berkeley environmental law professor Eric Biber.

Biber co-authored a paper with environmental scientist Diana Six that suggested waiting to see what bark beetles could tell us about climate change, and how trees might fight back.

“The argument would be that the trees that survive bark beetle infestations are likely to be adapted to better resist. Those are the trees that will reproduce going forward, so over time the beetles will select for the trees that are best able to resist them,” Biber says.

Basically, they want to let natural selection run its course.

“We will not be as effective in selecting for bark beetle resistances as the beetles themselves will be.”

So, Biber suggests slowing down and considering all the options. But he admits it’s hard to sit by when beautiful green vistas around California are starting to fade away.

“A lot of places in ecosystems that we're used to living with, that we associate looking a certain way and feeling a certain way will start changing, and we'll have these urges to do something about it. And it's not clear to me that we will be doing good things,” says Biber.

On the ride back down from Danny Prather’s land on Cobb Mountain, I pass the Boggs Mountain Demonstration State Forest. It was a public recreation area, but there was a lot of research that took place on the mountain too.


Now it’s completely charred — 90 percent of the trees burned in the Valley Fire.


For many here in Lake County, the view is a constant reminder of the huge loss the fire brought to this community.  


But some people see an opportunity. The forest could be a blank slate: a place to plant and test different trees that could resist future bark beetle attacks. And maybe, to find a way to manage the bark beetle-fueled epidemic by planting trees instead of cutting them down.


This story originally aired in March of 2016 and has since been updated.