After more than a century of fire suppression in California forests, researchers are examining the effects of prescribed burning and other controlled fire practices on forest health and carbon storage. A new long-term study from the University of California, Berkeley finds that while prescribed burning releases carbon dioxide in the short term, repeated use over decades can increase a forest’s ability to store carbon by maintaining large, fire-resistant 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 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 offers information for policymakers and land managers as California works toward its goal of net zero carbon pollution by 2045. According to John Battles, professor of forest ecology at UC Berkeley and senior author of the study: “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 experiment was conducted at Blodgett Forest Research Station in the Sierra Nevada starting in 2000. Researchers used various management techniques—prescribed burning and restoration thinning—on different plots for two decades. Other plots were left untouched as controls.
Field work measured how each approach impacted both overall carbon storage and net productivity—the rate at which forests remove atmospheric carbon through plant growth. While control plots retained higher levels of stored carbon throughout much of the study period, those treated with regular prescribed burns showed significant gains in net productivity after three treatments. By this point, increases in productivity nearly compensated for initial losses from released carbon during 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.”
To understand how much carbon each treatment affected across all parts of the ecosystem—from decaying needles on the ground to thick tree trunks—researchers tracked multiple pools where carbon is stored or released.
“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 led to an increase in small shade-tolerant species like incense cedar and white fir in Sierra Nevada forests. These species contribute dense understory growth that can turn small ground fires into severe crown fires—a risk mitigated by prescribed burns favoring larger pines.
“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.
Previous findings by this team showed that combining mechanical thinning with prescribed burning is most effective for reducing wildfire risk but carries higher immediate costs in terms of released carbon.
These results help communities weigh trade-offs between maximizing wildfire prevention near populated areas using both methods versus focusing solely on prescribed burning deeper within wilderness areas where retaining stored forest carbon is also important.
“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 (UC Berkeley), along with Emily Moghaddas (U.S. Department of Agriculture Forest Service).
