Clear-cutting forests could release tons of carbon into the atmosphere.

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When we talk about carbon dioxide in the atmosphere, we’re not talking about all the carbon that exists on earth. There are a number of natural factors that reduce the amount of CO2 in the atmosphere by sequestering carbon: trees and other plants, as well as the ocean and soil.

A recent study from Dartmouth College shows the importance of soil as a carbon sequestration medium.

Soil provides the largest land-based carbon pool, trapping more carbon than plants, though it does so in conjunction with those plants. It turns out that the soil of forests, especially mature forests, can sequester more carbon than other soils.

It’s important to understand that, when we talk about how much CO2 is in the atmosphere, and how bad it is, those numbers, and the effects of carbon dioxide, could be much worse. The reason that there’s so much carbon dioxide in the atmosphere is because soil, plants, and water are being pushed to the limits of how much carbon they can sequester.

Thus, clear-cutting, the act of cutting down whole areas of a forest, instead of selecting individual trees to be harvested, poses a huge risk. It can unleash a lot of carbon into the atmosphere, where it bonds with oxygen and becomes carbon dioxide.

“Clear-cutting forests has an effect of mobilizing the carbon, making it more likely to leave the soil and end up in the atmosphere,” says study senior author Andrew Friedland, a professor of environmental studies at Dartmouth.

It seems likely that clear-cutting throughout history may have helped contribute to current CO2 levels, by releasing the carbon stored in the soil, and then removing that soil—not to mention the forest—as a potential carbon pool.

Clear-cutting is a notoriously poor way to manage forests, but it’s also usually done in order to clear land for agriculture or construction, not simply to harvest lumber. We are now realizing just how much impact this process can have on the overall health of our climate.