Scientists identify the cause of tree mortality in the Amazon

As the climate continues to shift, the carbon storage capacity of the Amazon rainforest will be largely determined by how quickly trees die. A new study from the University of Birmingham has identified the factors that drive tree mortality rates. The research is providing new insight into why an increasing number of trees are dying across the Amazon basin.

“Understanding the main drivers of tree death allows us to better predict and plan for future trends – but this is a huge undertaking as there are more than 15,000 different tree species in the Amazon,” said study lead author Dr. Adriane Esquivel-Muelbert.

The study revealed that the main driver of Amazon tree mortality is the average growth rate of the tree species, with faster-growing trees dying at a younger age. 

The findings have major implications for the future of the Amazon forest, especially given that climate change promotes fast-growing species. If the forests selected by climate change are more likely to die young, they will also store less carbon.

“We found a strong tendency for faster-growing species to die more, meaning they have shorter life spans,” said Dr. David Galbraith. “While climate change has provided favourable conditions for these species, because they also die more quickly the carbon sequestration service provided by Amazon trees is declining.”

It requires a massive amount of data to investigate tree mortality. The RAINFOR network has assembled more than 30 years of contributions from more than 100 scientists. The database includes records from 189 one-hectare plots that were visited every 3 years. During each visit, the researchers measured trees above 10 centimeters in diameter and documented their condition. 

Overall, more than 124,000 living trees were followed, and 18,000 tree deaths recorded and analyzed. When a tree dies, there is a certain protocol that is used to identify the cause of death. “This involves detailed forensic work and amounts to a massive ‘CSI Amazon’ effort conducted by skilled investigators from a dozen nations,” said Professor Oliver Phillips.

In collaboration with the University of Leeds, the Birmingham study represents the first large scale analysis of the causes of tree mortality in the Amazon.

“Now that we can see more clearly what is going on across the whole forest, there are clear opportunities for action,” said 

Dr. Beatriz Marimon. “We find that drought is also driving tree death, but so far only in the South of the Amazon. What is happening here should serve as an early warning system as we need to prevent the same fate overtaking trees elsewhere.”

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer