Scientists find out how and why Amazonian trees are dying

The ability of the Amazon rainforest to store carbon in a changing climate will ultimately be determined by how quickly trees die and what kills them. Today, a large-scale new study has uncovered what factors control tree mortality rates in Amazon forests and helps explain why tree mortality is increasing in the Amazon basin.

This extensive analysis found that the average growth rate of tree species is the primary risk factor for Amazon tree death, with faster growing trees dying at a younger age. These results have important implications for our understanding of the future of these forests. Climate change tends to select fast growing species. While forests selected by climate change are more likely to die younger, they will also store less carbon.

The study, co-led by the Universities of Birmingham and Leeds in collaboration with more than 100 scientists, is the first large-scale analysis of the causes of tree death in the Amazon and uses long-term records collected by the international RAINFOR network .

The results published in Nature’s communications, show that species-level growth rates are a key risk factor for tree mortality.

“Understanding the main drivers of tree death allows us to better predict and plan for future trends – but it’s a huge undertaking because there are over 15,000 different tree species in the Amazon,” the author said. Principal Dr. Adriane Esquivel-Muelbert, Birmingham Forestry Research Institute.

Dr David Galbraith, University of Leeds, added: “We have found a strong tendency for faster growing species to die more, which means they have a shorter lifespan. climate change has provided favorable conditions for these species, as they also die off faster. The carbon sequestration service provided by Amazonian trees is in decline. “

Tree mortality is a rare event, so to really understand it requires huge amounts of data. The RAINFOR network has gathered more than 30 years of contributions from more than 100 scientists. It includes records of 189 one-hectare plots, each visited and monitored on average every 3 years. On each visit, the researchers measure all trees over 10 cm in diameter as well as the condition of each tree.

In total, more than 124,000 living trees have been monitored and 18,000 tree deaths have been recorded and analyzed. When trees die, the researcher follows a fixed protocol to unravel the real cause of death. “It involves detailed forensic work and amounts to a massive ‘CSI Amazon’ effort by trained investigators from a dozen countries,” noted Professor Oliver Phillips, University of Leeds.

Dr Beatriz Marimon, from UNEMAT, who coordinates several plots in central Brazil, added: “Now that we can see more clearly what is happening throughout the forest, there are clear possibilities for action. We find that drought also kills trees. , but so far only in the southern Amazon. What is happening here should serve as an early warning system because we must prevent the same fate from overtaking the trees elsewhere. ”