Prescribed burning, a method used to manage forests in California, has been shown in a new long-term study to help maintain large, fire-resistant trees and boost the ability of forests to store carbon over time. This research comes as policymakers look for ways to reduce wildfire risk and meet the state’s target of net zero carbon emissions by 2045.
While prescribed burns release carbon dioxide into the atmosphere initially, the study found that regular use of controlled fire can increase forest productivity in the long term. “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 the University of California, 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.”
John Battles, professor of forest ecology at UC Berkeley and senior author on the paper, added: “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 research took place at Blodgett Forest Research Station in the Sierra Nevada beginning in 2000. Researchers applied various management techniques including prescribed burning and restoration thinning on different plots for two decades while leaving others untouched for comparison.
They tracked changes by measuring all sources and sinks of carbon across different types of vegetation and fuel classes within each plot. According to Battles: “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. It really is just like a massive accounting job, except we’re not measuring money, we’re measuring carbon.”
Results showed that while untouched plots held more total carbon throughout most of the study period, repeated prescribed burns significantly increased net productivity after multiple treatments—nearly offsetting initial losses from combustion by promoting growth among remaining resilient trees. “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.”
The buildup of small shade-tolerant trees in areas where fire has been suppressed creates conditions for severe wildfires; prescribed burns help shift composition toward larger pines less likely to fuel intense fires.
Scott Stephens, co-author and Berkeley professor of fire science noted: “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.”
A previous study from this team indicated combining mechanical thinning with burning is best for reducing wildfire hazards but carries higher immediate carbon costs.
These findings offer guidance for communities balancing safety against environmental goals: combining thinning with burning near populated or sensitive areas maximizes protection; elsewhere deeper in wilderness areas prescribed burns alone may be preferred.
“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 trade-offs explicit so we can pick the right approach.”
Other contributors included Daniel Foster, Brandon Collins, Robert York, Ariel Roughton and John Sanders (all UC Berkeley), along with Emily Moghaddas from U.S. Department of Agriculture Forest Service.
