Controlled burns reduce carbon emissions from soil

A new study from the University of Cambridge reveals that controlled burns in forests, savannahs and grasslands could substantially offset carbon emissions. The experts report that prescribed burning can lock in – or even increase – carbon in the soils of natural environments.

The researchers say their discovery points to a new method of manipulating the world’s natural capacity for carbon capture and storage.

“Using controlled burns in forests to mitigate future wildfire severity is a relatively well-known process. But we’ve found that in ecosystems including temperate forests, savannahs and grasslands, fire can stabilise or even increase soil carbon,” said study first author Dr. Adam Pellegrini.

“Most of the fires in natural ecosystems around the globe are controlled burns, so we should see this as an opportunity. Humans are manipulating a process, so we may as well figure out how to manipulate it to maximize carbon storage in the soil.”

When soil is impacted by fire, carbon is released from plant matter and organic layers stored within. It takes years for this soil carbon to build back up.

According to the researchers, fires can also cause other transformations within soils that can offset these immediate carbon losses, and may stabilize ecosystem carbon.

Carbon is stabilized within the soil in multiple ways. It creates charcoal that is resistant to decomposition, and increases the amount of carbon that is bound tightly to minerals in the soil.

The study suggests that cooler fires can increase the retention of soil carbon through the formation of charcoal and soil clusters that limit decomposition.

“Ecosystems can store huge amounts of carbon when the frequency and intensity of fires is just right. It’s all about the balance of carbon going into soils from dead plant biomass, and carbon going out of soils from decomposition, erosion, and leaching,” said Dr. Pellegrini.

The scientists say that ecosystems can also be managed to increase the amount of carbon stored in their soils. Since carbon is often stored in the roots of plants below the ground, controlled burns can boost the amount of carbon stored by increasing root biomass.

“In considering how ecosystems should be managed to capture and store carbon from the atmosphere, fire is often seen as a bad thing,” said Dr. Pellegrini. “We hope this new study will show that when managed properly, fire can also be good – both for maintaining biodiversity and for carbon storage.”

The research was funded by the Gatsby Charitable Foundation. The results are published in the journal Nature Geoscience.

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By Chrissy Sexton, Earth.com Staff Writer