The carbon storage capacity of natural ecosystems is not maximized by planting trees or suppressing wildfires. A new study shows that prescribed burning can increase or lock in carbon in soils of temperate forests and savannahs.
This finding points to a new way to manipulate the world’s natural carbon capture and storage capacity. It can also help maintain natural ecosystem processes. The journal Nature Communications published the results today. Nature Geoscience.
“Using controlled fires in forests to reduce wildfire intensity is a well-known practice. However, we have found that fire can stabilise, or even increase, soil carbon in ecosystems such as temperate forests, savannahs, and grasslands,” said Dr Adam Pellegrini, University of Cambridge’s Department of Plant Sciences. He was the first author of this report.
He stated that most fires in natural ecosystems around Earth are controlled burns. We should therefore see this as a potential opportunity. Humans are manipulating a process. It is worth trying to figure out how to maximize carbon storage in soil.
In severe wildfires, fire can cause soil erosion and leaching of carbon by burning plant matter and organic layers. It can take many years, or even decades, for soil carbon to re-accumulate. However, researchers believe that fires may also cause soil changes that can offset the immediate carbon loss and may stabilize ecosystem carbon.
There are many ways that fire can stabilize carbon in soil. It creates charcoal which is very resistant against decomposition. Additionally, it forms ‘aggregates,’ which are physical clumps that can protect the soil’s carbon-rich organic material at its centre. The soil’s carbon can also be increased by using fire to increase its tightness to the minerals.
“Ecosystems can store large amounts of carbon when they are able to maintain a high level of fires. It’s all about the balance between carbon going into soils as dead plant biomass and carbon going out through decomposition, erosion and leaching,” stated Pellegrini.
In densely planted forests, fires can be too intense or frequent. They burn all the plant material that would otherwise decay and release carbon into the soil. High-intensity fires can also cause soil destabilization by separating carbon-based organic matter and minerals, and killing soil bacterias and fungi.
Soil carbon can be recycled without fire — organic matter from plants is consumed and released by microbes as carbon dioxide or methane. However, it is possible to retain soil carbon by using cooler fires. This can be done through the formation charcoal and soil aggregates which protect against decomposition.
Scientists say ecosystems can also managed to increase carbon storage in their soils. Most of the carbon found in grasslands is below-ground, in the roots. Controlled burning, which encourages grass growth, can increase root biomass to increase carbon storage.
“FIRE is often seen as something bad when it comes to how ecosystems should be managed to capture carbon from the atmosphere. Pellegrini said that fire can be beneficial for both biodiversity preservation and carbon storage if it is managed well.
The study was focused on carbon in topsoils. These are soils less than 30cm thick. The soil of the world holds more carbon than the global vegetation and atmosphere combined. Fire is an important part of global carbon cycling.
This research was funded in part by the Gatsby Charitable Foundation.