A Single Fire Killed Thousands Of Sequoias. Scientists Are Racing To Save The Rest

Sep 17, 2021
Originally published on September 20, 2021 5:02 am

On a hot afternoon in California's Sequoia National Park, Alexis Bernal squints up at the top of a 200-foot-tall tree.

"That is what we would call a real giant sequoia monarch," she says. "It's massive."

At 40 feet in diameter, the tree easily meets the definition of a monarch, the name given to the largest sequoias. It's likely more than 1,500 years old.

Still, that's as old as this tree will get. The trunk is pitch black, the char reaching almost all the way to the top. Not a single green branch is visible.

"It's 100% dead," Bernal says. "There's no living foliage on it all."

The scorched carcasses of eight other giants surround this one in the Alder Creek grove. A fire science research assistant at UC Berkeley, Bernal is here with a team cataloguing the destruction.

It's not easy to kill a giant sequoia. They can live more than 3,000 years and withstand repeated wildfires and droughts over the centuries.

Alexis Bernal of UC Berkeley is with a team of researchers measuring the burned sequoias and trying to understand how so many died.
Lauren Sommer / NPR

Now, with humans changing both the climate and the landscape surrounding the trees, these giants face dangers they might not survive.

Last year, the Castle Fire burned through the Sierra Nevada, fueled by hot, dry conditions and overgrown forests. Based on early estimates, as many as 10,600 large sequoias were killed — up to 14% of the entire population.

"This is unprecedented to see so many of these large old-growth trees dead, and I think it's a travesty," says Scott Stephens, fire scientist at UC Berkeley, as he surveys the damage. "This is pure disaster."

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With extreme fires increasing on a hotter planet, scientists are urgently trying to save the sequoias that remain. Researchers from federal agencies and universities are teaming up to find the sequoia groves at highest risk. The hope is to make them more fire-resistant by reducing the dense, overgrown vegetation around them, before the next wildfire hits.

But one year later, the sequoia groves are again under threat. At the time of publication, wildfires burning in Sequoia National Park are within a mile of a grove with thousands of sequoias. Firefighters are battling to contain the blazes.

"It's hard to see these trees that have lived hundreds to potentially thousands of years just die," Bernal says, "because it's just not a normal thing for them."

Living more than 3,000 years, giant sequoias normally survive dozens of low-grade wildfires in their lifetimes by towering over the rest of the forest. These barely escaped the Castle Fire in 2020.
Lauren Sommer / NPR

Sequoias need fire, but fires are changing

Giant sequoias only grow in isolated pockets, tucked in the mountains of California. Losing even a few groves spells significant loss to the entire population.

Sequoias are one of the most fire-adapted trees on the planet. With tough, foot-thick bark, they're insulated from the heat. They tower above the rest of the forest and the bottom of the tree is bare, without low branches that might be ignited by trees burning around it.

Old-growth sequoias weathered the low-intensity wildfires that were once the norm in the Sierra Nevada. Fires regularly spread along the forest floor, either ignited by lightning or set by Native American tribes who used burns to shape the landscape and cultivate food and materials.

With the arrival of white settlers, fire began to disappear from these forests. Tribes were forcibly removed from lands they once maintained, and federal firefighting agencies mounted a campaign of fire suppression, extinguishing blazes as quickly as possible.

That meant forests grew denser over the last century. Now, the built-up vegetation has become a tinder box, fueling hotter, more extreme fires, like the Castle Fire, that kill vast swaths of trees.

"These trees have been here 1,500 years, so how many fires have they withstood: 80?" Stephens says. "And then one fire comes in 2020 and suddenly they're gone."

Over many decades studying sequoias, Nate Stephenson had never seen old-growth sequoias die in large numbers until recently. "That's just unheard of," he says.
Lauren Sommer / NPR

The Castle Fire's fierce heat was also fueled by the changing climate. In 2012, when a drought hit California, hotter temperatures amplified the toll it took on Sierra Nevada forests. While the largest sequoias could handle it, other kinds of conifers around them succumbed. Millions of trees were killed.

"The extra warmth that came with the drought pushed it into a whole new terrain," says Nate Stephenson, an emeritus scientist with the U.S. Geological Survey. "That's what really helped kill a lot of trees, and they became fuel for fires."

During his four decades of studying sequoias, Stephenson had rarely seen an old-growth sequoia die. When the first images emerged after the Castle Fire hit, he wasn't prepared.

"That's when I couldn't help it," he says. "I don't cry often, but I cried when I saw the photos. Because I love these trees."

In some sequoia groves, few seedlings are being found in the aftermath of the Castle Fire. Those that have sprouted face surviving a summer of extreme drought.
Lauren Sommer / NPR

Few seedlings sprout from the ash

The soil is still powdery black in the Alder Creek sequoia grove a year later. The UC Berkeley team is scanning it for signs of hope: a spot of green.

"Two tiny sequoias here growing from the regeneration from the fire," Stephens says, finding 2-inch-tall seedlings, impossibly tiny compared to what they could become.

The lifecycle of a sequoia hinges on wildfire, which is the trigger for releasing its seeds. The blast of heat opens the cones, sending a shower of seeds to the forest floor, which get established quickly on the newly cleared ground.

In some groves, researchers are finding hundreds of seedlings where the Castle Fire burned with low intensity, the kind of fire sequoias are accustomed to.

But in the Alder Creek grove, where the fire burned with ferocious heat, the team only finds a dozen seedlings the entire afternoon. Other groves look similarly bare.

UC Berkeley's Holden Payne gathers data about the density of trees in the Alder Creek sequoia grove. Sequoia cones only release their seeds during wildfires.
Lauren Sommer / NPR

Even under normal conditions, around 98% of sequoia seedlings die in their first year. This year could be even tougher with extreme drought gripping the landscape.

"I am very concerned that some areas will not have sequoias," says Christy Brigham, head of resource management and science for Sequoia and Kings Canyon National Parks. "All the adults are killed and there will not be enough seedlings to repopulate."

That's leading land managers to consider planting new sequoias, so the scorched groves don't disappear entirely. But in a changing climate, it's not a simple question. As temperatures rise, young trees planted today face surviving in a vastly different future. The most suitable habitat for sequoias could move somewhere else.

"That is one of the gifts of giant sequoias — is that they force us to think in deep time," says Brigham. "It forces us to confront the challenge of climate change."

Researchers, including Scott Stephens (left), hope to identify which sequoia groves are most at risk from extreme fires in the hope of making them more fire-resistant.
Lauren Sommer / NPR

Rush to save remaining sequoias

Federal land managers say that given the millennia-length timeframe, planting new sequoias is a back-up plan at this point. The more pressing need is saving the trees that are left.

A coalition of the National Park Service, U.S. Forest Service, universities, tribes and nonprofits is banding together to identify the groves most at risk. This summer, the Giant Sequoia Lands Coalition has been rapidly assessing conditions on the ground.

"We just saw what one wildfire did," Brigham says. "Can we find the places, do the plans, and get the funding and put the people on the ground fast enough to prevent loss like this in the future?"

Brigham estimates around 40% of the sequoia groves on national park land alone are at risk of severe wildfires, because the surrounding forests haven't burned in decades. Other groves at risk are found on Forest Service or private land.

Many of the conifers within the sequoia groves were killed by California's previous drought, making them primed to burn in wildfires.
Lauren Sommer / NPR

Sequoia National Park has used controlled burns, also known as prescribed fire, since the 1960s to prevent forests from becoming overgrown. But Brigham says burning continues to be a challenge.

In the spring, when cooler conditions are better for controlled burning, projects are limited because of the threatened pacific fisher. The slender, mink-like animal was listed as endangered in 2020, and its habitat is protected during the spring denning season.

But burning in the summer can be tough because of air quality concerns, extremely dry vegetation or lack of personnel, since they're generally fighting wildfires.

"There are all these constraints on prescribed fire that we can't control," Brigham says. "As it gets hotter and drier, that window is smaller and smaller."

Brigham says she's hopeful that land managers can move quickly over the next year to prioritize the sequoia groves that need help the most. With extreme fires increasingly common, time is running short.

"It is not too late," says Brigham. "We can do better. People love these trees. So I just hope we can take that love and translate it into immediate action to protect the groves and long term action to limit climate change and its impacts."

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NOEL KING, HOST:

California's wildfires are threatening some of the biggest trees in the world. The giant trees in Sequoia National Park can live for more than 3,000 years. But last year, a fire killed more than 10% of all of the sequoias. Scientists are now desperately trying to protect the others. Here's NPR's Lauren Sommer.

LAUREN SOMMER, BYLINE: It's not easy to kill a giant sequoia. The trees are among the largest living things on the planet.

ALEXIS BERNAL: That is what we would call a real giant sequoia monarch.

SOMMER: Alexis Bernal is standing next to that monarch, the name given to the oldest sequoias. She's a research assistant at UC Berkeley.

BERNAL: It's massive. Jenny, what was the diameter on this tree?

SOMMER: The trunk is 40 feet around. But it's pitch-black, scorched all the way to the top.

BERNAL: It's a hundred percent dead. There's no living foliage on it at all. Within just a hundred meters of us, I can see one, two, three, four, five, six, you know, seven, eight, you know, giant sequoia monarchs. And they're all dead.

SOMMER: Last year, the Castle Fire tore through these sequoia groves. It killed thousands of trees, as much as 14% of the entire population based on early estimates.

BERNAL: It's hard to see these trees that have lived hundreds to potentially thousands of years just die because it's just not a normal thing for them.

SOMMER: Not normal because sequoias can handle fire. Their bark is a foot thick. They tower over the rest of the forest without any low branches that might ignite.

SCOTT STEPHENS: These trees have been here 1,500 hundred years. So how many fires have they maybe withstood? Eighty?

SOMMER: Scott Stephens is a fire scientist at UC Berkeley. He says low-grade fires used to happen in these forests regularly, either from lightning strikes or used by Native American tribes to cultivate the land. But for the last century, fires were extinguished. The forests got a lot denser. And in a hotter climate, that's fueling extreme fires, the kind that can kill these giants. The research team is here to inventory the damage. But they're also looking for signs of hope.

STEPHENS: Two tiny sequoias here growing from a regeneration from the fire.

SOMMER: In the ashy dirt, Stephens finds tiny, green sprouts just an inch tall. Sequoias only release their seeds during a fire. The heat is what opens the cones. But the whole day we're there, the team only finds a dozen seedlings. They'd normally expect to see hundreds or thousands.

STEPHENS: Unless we see some regeneration of some of these sites, my goodness, you're not going to see sequoia here.

SOMMER: Climate change set the stage for the Castle Fire, says Nate Stephenson, who studied sequoias for decades as a scientist with the U.S. Geological Survey. Temperatures are rising. And in 2012, a drought hit. That turned the pine trees around the sequoias into kindling.

NATE STEPHENSON: The extra warmth that came with the drought pushed it into a whole new terrain. And that's what really helped kill a lot of trees. And they become fuel for fires.

SOMMER: This year, the sequoia seedlings that did sprout are contending with another hot, dry summer. Stephenson says most will not survive.

STEPHENSON: You have to wonder, well, what is going to happen there if we do nothing? There is talk maybe we need to go in there and plant trees seedlings to try to ensure that we get some trees back.

SOMMER: But the big question is, if you plant a tree that survives thousands of years, can it survive the climate it'll be living in then?

CHRISTY BRIGHAM: That is one of the gifts of giant sequoias - is that they force us to think in deep time. It forces us to confront the challenge of climate change.

SOMMER: Christy Brigham is head of resource management for Sequoia and Kings Canyon National Parks. She says planting new sequoias would be the backup plan. Right now, they're trying to protect the sequoias that are left. Her team, along with other federal agencies, are figuring out which groves are most at risk. Then they'll use controlled burns or other tools to make them more fire-resistant.

BRIGHAM: It is not too late. We can do better and - sorry. And people love these trees. So I just hope that we can take that love and translate it into immediate action.

SOMMER: Because the worst-case scenario is a Sequoia National Park with no sequoias. Lauren Sommer, NPR News. Transcript provided by NPR, Copyright NPR.