Giant sequoias are built to live with fire. Their thick, spongy bark shields the underlying wood from flames. The lower trunks are largely devoid of foliage, offering little fuel to help fires reach the canopy. Heat pops open their dense cones, releasing seeds for the next generation.
But today’s fires, supercharged by climate change and underbrush left by decades of fire suppression, are too much even for these long-lived behemoths. In 2020 and 2021 wildfires in western California raged through sequoia groves, killing thousands of the trees in Sequoia and Kings Canyon national parks.
In the aftermath scientists are learning that the most effective way to help save these trees is to fight fire with fire. In places within the parks where land managers had reduced underbrush by intentionally setting low-intensity fires, sequoias were 77% less likely to die, according to new research in Nature Communications.
“Prescribed burns are effective at reducing giant sequoia mortality, even for today’s extreme wildfires,” said lead author Dan Dixon, who was a University of California Davis postdoctoral researcher when the study was conducted. “If the goal is protecting giant sequoias, prescribed fire is an essential tool.”
Prescribed fires have long been considered a critical—if underutilized—strategy for turning down the temperature in today’s era of megafires. The aim is to return fire-adapted forests to something closer to the conditions in which many of them evolved, when fires often acted more like cleansers than destroyers.
Triggered by lightning or Indigenous peoples, flames would regularly burn through forest understories, turning bushes and fallen trees to ash while leaving big, healthy trees relatively unscathed. Rarely, it’s thought, did they spawn the canopy-destroying firestorms of recent years, fueled by dense undergrowth left from a century of aggressive fire suppression.
Despite the reported benefits of prescribed fire, the effect at a very detailed level, such as the fate of an individual tree species, hadn’t been clearly demonstrated. Then, the Castle (2020) and KNP Complex (2021) fires happened. Over two years, these fires burned more than 1,000 square kilometers of forest in California’s Sierra Nevadas. That included some of the last remaining groves of the giant sequoia, a species found only in that region. The largest tree species on Earth, they can live more than 3,000 years and grow to the mass of 15 blue whales. In those two years, as many as 13,000 sequoias are thought to have perished.
“These trees live for so long and have experienced so much variability of climate, differences in wildfire, drought—they’ve seen it all,” Dixon said. “Having so many die in just two years was unprecedented.”
It also offered scientists an unusual opportunity. Since the 1960s, park managers had used prescribed burning in some of the sequoia groves. This gave researchers a chance to compare the fates of trees in landscapes that had been intentionally burned, and ones that had been untouched by fire for years until the devastating wildfire struck.
To tease out the differences, researchers used high-resolution satellite images that could show individual trees. They then trained a computer program to pick out giant sequoias and distinguish between live and dead trees before and after the fires. Finally, images of the forest created using LIDAR, a powerful imaging technique capable of peering through foliage, enabled the scientists to discern details including tree heights, spacing and other details about the forest structure.
All told, they examined 19 sequoia groves in the national parks totaling an estimated 26,403 of the giant trees. They spotted almost 8,000 trees killed by the fires – nearly a third of all the trees. The prescribed burning turned out to be a major factor in whether trees lived or died. In groves where a prescribed burn had been done within the previous decade, there was a 77% lower chance of a tree dying from the fires, according to a statistical model paired with the observations. There was even a notable benefit in places where the prescribed fire had happened between 10 and 15 years earlier.
If all the trees had been treated with prescribed burns, the scientists estimate it would have saved another 3,900 sequoias.
Though the new findings provide strong evidence for the benefits of burning, that’s not the case for other popular forms of forest treatments, such as selective logging to thin out overcrowded forests. While none of the groves had received such thinning, the scientists attempted to simulate the potential effects by looking at the LIDAR data to compare tree deaths in places with different forest structure – such as the density of trees. Those factors appeared to have no effect on the likelihood of sequoias dying.
That doesn’t mean such treatments are of no value, the scientists cautioned. It’s possible that fire conditions were so extreme that it erased benefits that might appear in less severe fires. It’s also possible these ancient, more structurally complex forests benefit less from selective logging than previously logged forests that have grown back.
The main message is clear, however. If people want to help sequoias withstand future fires, they’re going to need to learn to love fire.
Dixon, et. al. “Previous prescribed burns saved thousands of ancient sequoias 1 during historically unprecedented wildfires.” Nature Communications. July 11, 2026.
Photo: ©Katherine E Kerlin
