This is a first for scientists. The number of trees covering a large area of sub-Saharan Africa was established precisely thanks to a method combining satellite observations and artificial intelligence, a study unveiled Wednesday in the journal Nature. This could improve the preservation of these carbon sinks. The data collected is a first step towards developing better safeguarding policies, by improving the monitoring of forest preservation programs by scientists and those investing in carbon credit projects.

Previous estimates had overestimated carbon storage, the researchers say. According to the study, there are 9.9 billion trees on a strip of dryland covering nearly 10 million km2 from the Atlantic Ocean to the Red Sea, roughly the size of China. This compares to about 400 billion trees in the Amazon.

More than 300,000 satellite images

In drylands, trees capture carbon much longer than herbaceous and other plant species in the region, even though, taken individually, they store relatively little. In the region studied, trees would store a total of 0.84 billion tons of carbon equivalent, the researchers calculate. In comparison, French forests retain some 2.4 billion tonnes.

Scientists used artificial intelligence to analyze more than 300,000 high-resolution satellite images to determine the area covered by the leaves of each tree in arid regions. This method "tells us about the carbon cycle and how much carbon trees contain that mitigates climate change," Compton Tucker, co-lead author of the study, told AFP.

Data to refine

"In green finance, there is a lot of money dedicated to avoided deforestation that has not been used for lack of a verification system," said Philippe Ciais, a researcher at the French Alternative Energies and Atomic Energy Commission (CEA), a participant in the study. The authors plan to refine the tool by including features on the tree's trunk, which should provide finer data on its age and height, parameters that influence carbon storage.

"It's not possible yet, but we're almost there," said Pierre Hiernaux, co-author of the study. The same methodology could be used in other drylands, including Australia, the western United States or Central Asia. It could help the "Great Green Wall" project, which aims to regenerate savannah, grasslands and farmland in the Sahel. An interactive online map allows you to explore the results.

  • Planet
  • Nature
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  • Deforestation