How Fire Saves Giant Sequoias

Giant sequoias exposed to prescribed burns during the preceding decade were nearly four times more likely to survive extreme wildfires in California’s Sierra Nevada, according to a University of California, Davis study published in Nature Communications. Researchers analyzed the impacts of the 2020 Castle Fire and the 2021 KNP Complex Fire, finding that proactive fuel reduction significantly protected ancient trees that can live for more than 3,000 years and weigh as much as 15 blue whales.

How Prescribed Burns Protected Giant Sequoias During Extreme Wildfires

Controlled burns carried out within the decade prior to the wildfires reduced a giant sequoia’s odds of dying by about 77 percent, according to the UC Davis study. Researchers examined roughly 26,400 giant sequoias across 19 groves affected by the Castle and KNP wildfires. By combining airborne lidar to measure forest structure with high-resolution PlanetScope satellite images, the scientific team reconstructed fuel conditions before the flames arrived.

Computer simulations conducted by the research team indicated that earlier prescribed burns prevented approximately 1,900 giant sequoia deaths during the 2020 and 2021 seasons. Furthermore, the analysis estimated that another 3,900 trees could have survived if every sequoia in the affected groves had received similar treatment before the fires started.

Evolutionary Adaptation Meets Modern Climate Pressures

Giant sequoias evolved on the western slopes of California’s Sierra Nevada in an environment shaped by periodic, low-intensity fires. Thick bark and elevated canopies historically protected mature specimens, while smaller fires cleared competing vegetation and recycled nutrients. However, some areas had gone without fire for more than 100 years, allowing dead wood, shrubs, and other combustible material to accumulate, transforming how high-severity fires impact these old-growth forests.

“These trees live for so long and have experienced so much variability of climate, differences in wildfire, drought — they’ve seen it all,” said lead author Dan Dixon, who worked as a UC Davis postdoctoral researcher in Professor Yufang Jin’s lab during the study. “Having so many die in just two years was unprecedented,” Dixon noted regarding the massive losses observed across the 2020 and 2021 fire seasons.

Future Conservation Strategies for Old-Growth Forests

Climate change is increasing the frequency and severity of disturbances affecting old-growth forests, including drought and extreme wildfire, threatening even naturally fire-resistant species. Coauthor Yufang Jin emphasized that combining scalable remote sensing with rigorous statistical frameworks offers vital insights that field surveys alone cannot provide. The findings demonstrate that active management remains necessary to preserve these ecosystems.

“If the goal is protecting giant sequoias, prescribed fire is an essential tool available to managers,” Dixon stated. The research team included scientists from UC Davis, the U.S. Geological Survey’s Western Ecological Research Center, and the Division of Resources Management and Science at Sequoia and Kings Canyon National Parks. Financial support for the project came from the NASA Land Cover and Land Use Change Program, the California Strategic Growth Council, and the USDA National Institute of Food and Agriculture.

Frequently Asked Questions

Why are giant sequoias vulnerable to modern wildfires?

In some areas, a lack of fire for more than 100 years led to a heavy accumulation of dead wood, shrubs, and fuels around ancient trees. When combined with severe disturbances driven by climate change, modern wildfires can become intense enough to overwhelm the natural defenses of even 3,000-year-old sequoias.

How much do prescribed burns improve survival rates?

According to the UC Davis study, giant sequoias exposed to prescribed burns within the prior 10 years were nearly four times more likely to survive extreme fires, with controlled treatments reducing mortality risk by approximately 77 percent.

Where do giant sequoias naturally grow?

In the wild, giant sequoias grow only on the western slopes of California’s Sierra Nevada.