After decades of fire suppression in California’s forests, researchers are finding that controlled burning can help maintain forest health and support the state’s climate goals. A new long-term study led by scientists at the University of California, Berkeley, shows that prescribed burning, while releasing carbon dioxide in the short term, may increase a forest’s ability to store carbon over time.
“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 study lead author Yihong Zhu, a graduate student at UC Berkeley. “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 research provides insights for policymakers and land managers who are trying to reduce wildfire risks while helping California reach its target of net zero carbon pollution by 2045.
“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,” said study senior author John Battles, professor of forest ecology at UC Berkeley. “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 draws on two decades of experiments at Blodgett Forest Research Station in the Sierra Nevada. Researchers applied various management techniques—including prescribed burns and restoration thinning—to different plots since 2000. Other plots were left untouched as controls.
Through fieldwork and lab analysis, scientists measured how each approach affected both carbon storage and overall productivity. They discovered that although control plots stored more total carbon, repeated prescribed burns significantly improved net productivity in treated areas. By the end of the study period, this gain nearly offset the initial carbon released by fires.
“After the first burn, the net productivity of those plots was really low and the controls looked a lot better,” said John Battles. “But by the third burn, the patterns had switched.”
Researchers tracked all forms of stored carbon—from decaying pine needles to large tree trunks—and accounted for all ways it could return to the atmosphere.
“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.”
Years without fire have led to an increase in smaller trees like incense cedar and white fir in Sierra Nevada forests; these species can turn small ground fires into larger ones by acting as “fuel ladders.” Prescribed burns can reverse this trend by promoting growth among larger pines known for their resistance to fire.
“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 co-author Scott Stephens.
A previous study from this team found that combining prescribed burning with mechanical thinning was most effective for reducing wildfire hazards but came with higher immediate carbon costs.
Taken together, these studies provide guidance for communities weighing their options for forest management. Where protecting people or iconic groves is paramount—such as near towns or giant sequoia habitats—a mix of thinning and burning may be best. In remote wilderness areas where maintaining stored carbon is key but human safety is less urgent, prescribed burning alone might be preferable.
“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 U.S. Department of Agriculture Forest Service also participated.
