Forest Carbon: Store it or Burn it? Actually, Both is Best
Storing carbon in forests is an essential, nature-based buffer against climate change. Yet forests packed with too many trees increase the threat of severe wildfires, which are becoming all too common in warmer, drier conditions.
A team of UC Merced and collaborating researchers evaluated the tradeoffs between two seemingly opposing scenarios:
Trees are critical because they pull carbon dioxide from the air and store it in their trunks, preventing carbon from adding to greenhouse effects that trap heat and warm the atmosphere.
The increasing severity and danger of wildfires call for the thinning of overly dense forests.
The researchers found that the best approach is a combination of both.
In a paper published in Ecological Modeling, they report that forests can provide wildfire safety and be effective carbon collectors if trees are selectively harvested and turned into long-lived wood products.
“Given the increasing risks of high-severity wildfire in our overstocked forests, and rapid growth of shrubs and small trees, it is becoming more important to periodically burn or remove small-diameter material to maintain wildfire security,” said co-author Safeeq Khan, a professor of watershed hydrology at UC Merced. “Our research provides information on the benefits of these management actions.”
The study, published in Ecological Modeling, looked at carbon storage and wildfire risk in the 2,000-square-mile American River basin. The basin has endured eight wildfires of more than 2,500 acres in the past quarter-century. Many areas are choked with small trees, the result of a century of fire suppression and unsustainable logging.
Using a dynamic ecosystem model, researchers tested how different management strategies — mechanical thinning and prescribed burning — affect the balance of carbon absorbed and released. They found that repeating these treatments every five to 20 years helps reduce fire danger, but prescribed burning alone often leads forests to emit more carbon than they capture.
That’s because while reducing wildfire severity cuts emissions, large-scale burning releases even more carbon. Forests only become reliable carbon sinks when thinning is paired with storing the harvested wood in long-lived products such as lumber.
Life and environmental sciences Professor Emeritus Stephen C. Hart, another co-author, said he was surprised at the models’ suggestion that widespread application of prescribed fire would increase carbon emissions despite reducing wildfire severity.
“Only through the use of ecosystem simulation models, such as the one used in this study, can the complex interactions among climate, wildfire, forest management and the carbon cycle be fully elucidated,” he said.
The findings highlight a key lesson: Forests can be both safer from fire and effective carbon banks, but only with active, balanced management.
“There is strong interest across California in increasing fuels treatments to reduce projected wildfire severity and protect built infrastructure, with huge co-benefits to water security, erosion reduction, hydropower, air quality, recreation, drought protection, habitat and other ecosystem services,” said co-author Roger Bales, professor emeritus of engineering at UC Merced.
The researchers concluded that the Sierra Nevada can remain a long-term carbon sink if land managers thin small trees, store carbon from harvested biomass in durable wood products, and use prescribed fire strategically.