Prescribed Fires Cut Sequoia Mortality by Up to 77% in 2020‑21 Wildfires

Two catastrophic wildfires swept through California’s Sierra Nevada in 2020 and 2021, claiming thousands of giant sequoias. A new University of California, Davis investigation reveals that groves treated with prescribed burns were dramatically more resilient, with losses far lower than they would have been without those controlled fires.

Published in Nature Communications, the research shows that giant sequoias exposed to prescribed fire within the preceding decade were roughly four times more likely to survive the extreme Castle Fire of 2020 and the KNP Complex Fire of 2021 than nearby untreated trees.

“Prescribed burns are effective at reducing giant sequoia mortality, even for today’s extreme wildfires,” said lead author Dan Dixon, who conducted the work as a UC Davis postdoctoral researcher in Professor Yufang Jin’s lab. “If the goal is protecting giant sequoias, prescribed fire is an essential tool available to managers.”

Ancient Giants Built for Fire

Giant sequoias rank among Earth’s largest and longest‑lived organisms. A single specimen can weigh as much as 15 blue whales and live for more than 3,000 years, growing only on the western Sierra Nevada slopes. These towering trees evolved in a fire‑shaped landscape, relying on thick bark, elevated canopies, and periodic low‑intensity burns that clear undergrowth and recycle nutrients, fostering new growth.

Historically, mature sequoias were considered nearly fire‑proof. That belief shattered after the 2020‑2021 fire seasons, when entire groves of centuries‑old trees lay charred, a stark reminder of the trees’ vulnerability under today’s extreme conditions.

“These trees live for so long and have experienced so much variability of climate, differences in wildfire, drought – they’ve seen it all,” Dixon noted. “Having so many die in just two years was unprecedented.”

Decades of Prescribed Burning Created a Natural Test

Sequoia and Kings Canyon National Parks have maintained one of the nation’s most extensive prescribed‑fire programs since the 1960s. Over decades, this effort created a patchwork of groves with divergent fire histories—some recently burned, others untouched for more than a century, allowing fuel to accumulate.

That variation offered researchers a rare opportunity to quantify how prior prescribed burns influence sequoia survival during extreme wildfires. Teams from UC Davis, the U.S. Geological Survey, and the two national parks combined airborne lidar, which maps forest structure with laser pulses, and high‑resolution PlanetScope satellite imagery.

The scientists examined pre‑fire fuel conditions and modeled the fates of roughly 26,400 giant sequoias across 19 groves impacted by the Castle Fire and KNP Complex Fire.

Prescribed Fire Cut the Risk of Death

Results delivered a striking survival advantage. Prescribed burns conducted within the previous ten years lowered a sequoia’s odds of dying by about 77%. Trees in treated areas were roughly four times more likely to survive than those in untreated portions of the same groves.

Computer simulations suggested that earlier prescribed burns prevented an estimated 1,900 sequoia deaths. The team further projected that an additional 3,900 trees might have survived if every sequoia in the affected groves had received similar treatment.

A Critical Tool for Sequoia Conservation

Climate change is intensifying disturbances to old‑growth forests, including drought and extreme wildfire. While giant sequoias remain naturally fire‑resistant, the study demonstrates that even these hardy species are vulnerable when flames reach extraordinary intensity. The findings strongly support the use of prescribed burning as a means to thin fuel loads, thereby protecting sequoia groves when major wildfires strike.

“This is a timely study given the history of fire suppression in these forests and the state’s increasing pace and scale of fuel thinning in recent years,” Jin explained. “By combining scalable, high‑resolution remote sensing with a rigorous statistical framework, we were able to reveal insights on the effects of prescribed fires that go well beyond what traditional anecdotes or field surveys can tell us.”

The study’s additional coauthors are Xiaoli Dong and Andrew Latimer of UC Davis, Adrian Das, David Soderberg and Nathan Stephenson of the USGS’ Western Ecological Research Center, and Anthony Caprio of the Division of Resources Management and Science at Sequoia and Kings Canyon National Parks.

The study was funded by the NASA Land Cover and Land Use Change Program, California Strategic Growth Council, and the USDA National Institute of Food and Agriculture.

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