The world's largest terrestrial carbon sinks are found in young forests

These trees have generally "pushed back" on land previously used for agriculture, or cleared by a fire or a crop, and it is their young age that is one of the main factors of this absorption. of carbon.

Forests are widely recognized as important carbon sinks – ecosystems capable of capturing and storing large amounts of carbon dioxide – but dense tropical forests, close to the equator, have been expected to work hard to absorb these gas.

Researchers at the University of Birmingham have conducted a new analysis of the global biosphere using a new combination of data and computer modeling as part of a new study published in the Proceedings of the National Academy of Sciences (PNAS). Based on forest age data sets, they were able to show the amount of carbon absorbed between 2001 and 2010 by the old established forest areas.

They compared this with younger forests that are reborn in areas that had previously experienced human activities such as agriculture or logging or natural disturbances such as fires.

Previously, it was thought that carbon uptake by forests was primarily due to the fertilization of tree growth by increasing levels of carbon dioxide in the atmosphere.

However, researchers have found that forest regeneration areas absorb large amounts of carbon, not only because of these fertilizing effects, but also because of their younger age. The effect of age accounted for about 25% of the total carbon dioxide absorbed by forests.

In addition, age-related carbon uptake was mainly localized not in the tropics, but in mid- and high-latitude forests.

These forests include, for example, land located in the eastern United States, where settlers created agricultural land and then abandoned it to move west in the late nineteenth century. The abandoned lands became part of the US National Forest, as were new areas abandoned during the Great Depression in the 1930s.

Other important areas of forest regeneration include boreal forests in Canada, Russia and Europe, which have experienced significant harvesting activity and forest fires. Large-scale afforestation programs in China also make a major contribution to this carbon sink.

Tom Pugh of the Birmingham Forest Research Institute (BIFoR) said: "It is important to understand where and why this carbon uptake occurs, as it helps us make informed and informed decisions about forest management. . "

The research highlights the importance of global temperate zone forests in mitigating the effects of climate change, but also shows more clearly the amount of carbon that these regenerating forests are expected to absorb in the future. This is particularly important because of the transient nature of forest regeneration: once the current pulse of forest regeneration has passed through the system, this important part of the carbon sink will disappear unless reforestation occurs. .

"The amount of CO2 that can be absorbed by forests is a finite amount: reforestation programs will ultimately be effective only if we simultaneously work to reduce our emissions," says Pugh.

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More information:
Thomas A. M. Pugh et al., "Role of forest regeneration in global carbon sink dynamics" PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1810512116