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Savannah is gaining ground in the heart of the Amazon, and that’s not good news

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Recent work shows an extension of the savannah even within the iconic tropical forest. A worrying imbalance that scientists link to the intensification of forest fires in the context of climate change. The results are published in open access in the scientific journal Ecosystems.

The savannah for the benefit of the tropical forest

The growth of areas dedicated to agriculture and livestock has led to the replacement of the Amazon rainforest by a savannah-type landscape. This limit known asdeforestation arc progresses rapidly and every year nibbles land through the southeast of the forest. However, according to recent work, the savannah is also gaining in surface in the heart of the Amazon, far from the agricultural domain and from any human action.

This is the case, for example, in the region surrounding Manaus, near the banks of the Rio Negro in northwestern Brazil. Indeed, over the past 40 years, the savannah has gradually taken the place of the tropical forest. Researchers who have identified these changes over an area of ​​around 4,100 km² link them to global warming.

More specifically, by promoting more severe droughts and fires, climate change weakens and slows the regrowth of forest trees. In particular, those located in the flood plains as we find a large number near the Rio Negro. As a result, these only very slowly repopulate the burnt areas compared to herbaceous and other native species which consequently occupy an increasing fraction of the land.

Passage from a forest (left) to a savannah (right). Credits: Bernardo M. Flores et al. 2021.

We mapped 40 years of forest fires using satellite imagery and collected detailed information on the ground to see if the burnt forest areas were changing. »Explains Bernardo M. Flores, lead author of the study. ” When we analyzed the various tree species and soil properties at different times in the past, we found that forest fires had killed virtually all trees, so the clay topsoil could be eroded by annual flooding. and become more and more sandy “.

The threat of ecosystem reorganization

Note that the savannah that extends inside the Amazon is not a completely new landscape since it was initially part of it. In fact, it represents around 10% of the undisturbed ecosystem. Also, it is the imbalance – in other words, the fact that the savannah is progressing – which constitutes a threatening element. Among other consequences, if such a plant permutation were to become widespread, it would lead in its wake a significant reduction in carbon in the form of CO2 towards the atmosphere.

Our research shows that the area of ​​native savannah is expanding and may continue to expand in the Amazon. Not along the deforestation arc, where exotic grasses are spreading, but in remote areas of the basin where these savannas already exist »Reports Bernardo M. Flores. ” Floodplain forests are the Achilles heel of the Amazon Adds Milena Holmgren, co-author of the paper. ” We have evidence from the ground that if the climate becomes drier in the Amazon and fires become more severe and frequent, floodplain forests will be the first to collapse. “.



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