After decades of suppressing wildfires in California’s forests, new research from the University of California, Berkeley suggests that using prescribed burning can help maintain large, fire-resistant trees and may increase the long-term ability of forests to store carbon.
The study, led by Yihong Zhu, a graduate student at UC Berkeley, tracked forest plots at the Blodgett Forest Research Station in the Sierra Nevada over a 20-year period. The researchers applied different management techniques—including prescribed burns and restoration thinning—to some plots while leaving others untouched. They found that unmanaged plots became less productive over time due to increased competition among trees and climate stress. In contrast, repeated prescribed burning maintained or even improved productivity by supporting larger trees.
“Over time, we found that the productivity of unmanaged tree stands decreased, likely due to increased competition and climate stress. Meanwhile, prescribed burning helped maintain large, fire-resistant trees, eventually increasing the productivity of these stands,” said Zhu. “We wouldn’t be able to detect such a benefit had we not been able to monitor these stands over 20 years and three entries with controlled fire.”
The findings are relevant for policymakers and land managers who aim to reduce wildfire risk while helping California reach its goal of net zero carbon pollution by 2045. John Battles, senior author and professor of forest ecology at UC Berkeley, said: “Nature-based climate solutions were a big focus of the 2024 Paris Climate agreement, and either maintaining or increasing forest carbon is one of the most cost-effective strategies. We found that, with some management, you may lower the total carbon storage of a forest, but you make it safer from loss from wildfires or pathogen outbreaks. We call it stable carbon.”
The study measured how each treatment affected both total carbon storage and net productivity—the amount of new growth added each year. While control plots kept more stored carbon overall because they were not disturbed by fire or thinning, plots that underwent three rounds of prescribed burning showed significantly higher net productivity by the end of two decades—almost enough to offset the initial release of carbon caused by burning.
“After the first burn, the net productivity of those plots was really low and the controls looked a lot better,” said Battles. “But by the third burn, the patterns had switched.”
The research team accounted for all sources and pools of carbon in their analysis—from decaying pine needles on the ground up to thick tree trunks—and traced how each changed over time after treatments.
“We looked at big trees, we looked at little trees, we looked at shrubs, we looked at different fuel classes, and then we checked how they changed,” said Battles. “It really is just like a massive accounting job, except we’re not measuring money, we’re measuring carbon.”
Fire suppression has allowed smaller shade-tolerant species like incense cedar and white fir to proliferate in Sierra Nevada forests; their dense understory can act as fuel ladders that enable fires to climb into treetops. Prescribed burns can reverse this trend—sometimes called “fir-ification”—by promoting more resilient species such as ponderosa pine.
“We’ve always wondered if we could restore these ecosystems to a more functional state—lower density and more frequent fire—do we eventually see a bonus? Do we get that golden nugget? And in this work, we were able to actually measure it,” said Scott Stephens, co-author and professor of fire science at UC Berkeley.
A previous study from this group showed that combining prescribed burning with mechanical thinning was most effective for reducing wildfire hazard but also resulted in greater immediate loss of stored carbon. The current findings suggest that communities should weigh trade-offs between wildfire prevention needs and long-term carbon storage when choosing management strategies.
“We’ve got to get these treatments out there,” Battles said. “Some treatments might be better than others in certain situations, but now we’ve made the trade-offs explicit so we can pick the right approach.”
Other contributors include Daniel Foster, Brandon Collins, Robert York, Ariel Roughton and John Sanders from UC Berkeley; Emily Moghaddas from the U.S. Department of Agriculture Forest Service.
