The key to protecting California’s giant sequoias from wildfire — controlled fires

When wildfires tore through the Sierra Nevada in 2020 and 2021, they burned thousands of giant sequoias at rates not seen for millennia.

But the destruction would have been far worse had the trees not undergone prescribed burns, according to a new UC Davis study published in Nature Communications.

“We estimate that giant sequoias with those prescribed burn treatments within the last 10 years ended up being about four times more likely to survive,” said Dan Dixon, who led the study as a UC Davis postdoctoral researcher.

In addition to being beloved namesakes of a popular national park, California's sequoias can store significant amounts of carbon, absorbing it from the atmosphere and making the trees a positive force in a changing climate. Climate change, however, is driving the kinds of fires and other threats that could reduce their numbers further.

The study

Using airborne sensing and satellites, the researchers gathered images of around 26,400 of the trees in Sequoia and Kings Canyon national parks before and after the fires. They then used neural networks, a type of artificial intelligence, to identify whether the trees were living or dead.

Dixon said the neural networks allowed the researchers to detect whether giant sequoias had survived based on factors like how green they were and what the canopy looked like. The neural network was trained on data collected from over 1,000 giant sequoias visited by researchers on the ground.

“This is kind of the future of this field, linking work like this: using imagery, but then also validating it on the ground,” said Ashley Grupenhoff, a fire ecologist at Cal Poly San Luis Obispo who was not involved in the study.

Hundreds of beloved giant sequoias survived wildfire because of prescribed burns, according to a new paper.

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UC Davis

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With researchers from the U.S. Geological Survey and the National Park Service, the team compared the images with areas with prescribed fire and found that the burns saved about 1,900 giant sequoias in the 2020 and 2021 wildfires. An additional 3,900 would have survived if all the trees had been treated, the study found.

“I think it did something that few other studies have, which is really looking at that individual tree level and mak[ing] causal inferences that really show the importance of prescribed fire,” Grupenhoff said.

The future of prescribed fire

Giant sequoias are adapted to resist low-intensity fires. But the study notes that with climate change increasing the frequency and ferocity of large fires, even these resilient trees are becoming more vulnerable. Setting more low-intensity fires could be integral to saving these trees from catastrophic wildfires, experts said.

Prescribed fire “burns off the susceptible material that wants to burn in a wildfire scenario when it’s hotter and drier and the winds are blowing faster,” said Jeffrey Stackhouse, an advisor at UC Agriculture and Natural Resources who was not involved in the study. “It makes trees a lot more resilient.”

In California, more than 120,000 acres are treated every year with prescribed burning conducted by Cal Fire and partner agencies, and controlled burning has been a longstanding tradition for some Indigenous tribes.

The 2020 Castle Fire in Sequoia National Park killed thousands of the park's namesake giant trees, some of which may have been more than 2,000 years old.

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Anthony Caprio

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National Park Service

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The study comes at a time when community-led efforts to conduct prescribed fires are increasing, experts said.

“A lot of communities are tired of waiting for someone to come do it for them,” said Lenya Quinn-Davidson, the director of the UC ANR Fire Network who was not involved in the study.

In 2017, Quinn-Davidson and Stackhouse started the first prescribed fire association in California. Today, dozens of volunteers conduct prescribed fires to clean up dry wood, leaves and other fuel as part of a “big social movement” around controlled burning, Quinn-Davidson said.

“It’s a big moment in time for this work,” Quinn-Davidson said.