Photo: Pixabay/9883074

Tropical forests, or what is left of them, are important carbon sinks, but boreal and temperate forests are just as important if not more.

This is the conclusion reached by an international research team, led by the French Alternative Energies and Atomic Energy Commission, which mapped annual changes in global forest biomass between 2010 and 2019.

Although tropical forests are older, they have been extensively reduced by deforestation, forest fires and droughts, which means they are nearly carbon neutral. That is why boreal and young forests are playing an increasingly key role for climate change mitigation strategies as their plant biomass grows, thereby aiding in more effective carbon sequestration.

“The carbon balance of biomass results from gains due to plant growth and increased forest cover and losses due to harvest, deforestation, degradation, background tree mortality and natural disturbances,” the scientists note in a statement on their findings.

“Monitoring biomass carbon stocks over time is essential to better understand and predict the effects of ongoing and future climate change, as well as the direct impacts of human activities on ecosystems. This is a key issue for climate change mitigation policies,” they stress.

In their research, whose results have been published in a study, the scientists drew on above-ground biomass data to determine the totality of biomass globally as of 2020. They then calculated the spatial and temporal distribution of all live biomass carbon of terrestrial ecosystems between 2010 and 2019. Finally they developed maps of annual biomass carbon change.

Globally, they report, terrestrial biomass carbon stocks increased within the studied nine years by some 500 million metric tons of carbon annually. “The main contributors to the global carbon sink are boreal and temperate forests, while tropical forests have become small carbon sources because of deforestation and tree mortality following periods of repeated drought,” they explain.”

Earlier research found that tropical forests are fast losing their effectiveness at storing carbon. However, research has also found that restoring these forests can boost their carbon sink capacity.

Currently, old-growth tropical forests where the average age of trees is more than 140 years old are nearly carbon neutral. At the same time, temperate and boreal forests, where trees are less than 50 years old or middle-aged (50-140 years old), are now the largest carbon sinks globally, according to this new study.

“The new findings differ from existing prediction models that show all old-growth forests to be large carbon sinks and do not account for the importance of forest demography or the impact of deforestation and degradation on tropical forests, which are losing biomass,” the scientists note.

Their results can be used for better predicting the dynamics of future carbon sinks worldwide to develop up-to-date climate change mitigation policies based on them, the researchers say.

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