FORESTS are carbon storage powerhouses. It’s easy, quite literally, to see why. All those towering trunks and spreading branches are formed from carbon that trees absorbed from the atmosphere and transformed into wood, roots and leaves.

Forests, however, have a second, often bigger, cache of carbon: the soil. Fifty-eight percent of a forest’s carbon is locked away underground. But when it comes to understanding how to protect and restore this enormous carbon stockpile, the science is far from settled.

This lack of understanding means it’s hard for forest managers to know how sustainable logging, controlled burns and other actions impact the carbon stored in forest soils. “This is a big bucket where there’s a lot of missing information,” DeLyser says.

For the last few years, American Forests and the Northern Institute of Applied Climate Science, a research branch of the United States Forest Service, have been conducting first-of-its-kind research on forest soil carbon across the country. The research will be used to produce detailed maps of soil carbon — where it’s highest and lowest, at risk of being lost, and the opportunities to restore it exist — as well as menus of actions foresters can take to manage the carbon hidden underfoot.

“Forest managers are constantly trying to balance different goals,” says Kendall DeLyser, American Forests’ senior manager of forests and climate. “Our tools will help them add in forest soil carbon to those decisions.” This research will benefit not only carbon-conscious foresters, but also policymakers, companies and other groups interested in investing in forests as a natural solution to climate change.

American Forests launched this research in 2018 by partnering with the Maryland Department of Natural Resources to collect and analyze scientific studies about the state’s forest soils. This research identified, among other things, the particular vulnerability of soil carbon on steep slopes and that shallow soils are more at risk of losing carbon than deep ones.

Now, American Forests is expanding this initiative to Oregon, Washington, Minnesota, Michigan, Wisconsin and North Carolina. In the Great Lakes states, American Forests is creating original maps of abandoned mines and pine plantations in need of forest restoration work, neither of which have been comprehensively mapped in this region before. In this particular region, DeLyser explains, physical factors, such as a soil’s texture and water retention, play a big role in how much carbon the soil contains. In contrast, in the Pacific Northwest, wildfires are one of the biggest influences on forest carbon, capable of incinerating not only trees but the organic matter stored in soil. Burned carbon returns to the atmosphere as carbon dioxide, where it exacerbates global warming.

For any forester worried that managing forest carbon will add more complexity to an already complex job, DeLyser has good news: “If you’re managing your forest sustainably, chances are you’re also managing the soil carbon well.” In the western U.S., for example, controlled burns are an important tool for restoring healthy forests and staving off extreme wildfires. Compared to the soil-scorching flames of giant, blistering wildfires, controlled burns only singe the upper layer of the forest floor, leading to much smaller, more predictable carbon losses.

If you are looking for a new tool to slow climate change and another argument for sustainable forestry, it turns out the answer was under our feet all along.