Climate change causes high tree mortality in the southern Amazon

Credit: Ben Hur Marimon Junior

A team of Brazilian and British scientists have found that extreme wind and lack of water are the main causes of tree death in the southern Amazon.

The study found that more than 70% of all trees that die at the edge of the Amazon rainforest already had severely broken and damaged crowns due to climate change years before they died, a significantly higher percentage than in other places. other regions of the Amazon.

In addition, the proportion of trees that die broken in this area is higher than anywhere else in the Amazon, at around 54%.

Research published this week in the Journal of Ecology is the first to assess the causes of tree mortality in the southern Amazon rainforest on a large scale using tree-by-tree data.

Researchers from the University of Leeds, the University of Oxford and the State University of Mato Grosso (UNEMAT) in Brazil investigated the death of nearly 15,000 trees in 19 study plots spread in the remaining forests on the southern edge of the Amazon. The region is the driest, hottest and most fragmented in the Amazon and has recently experienced several severe droughts.

Professor Oliver Phillips from the University of Leeds School of Geography and co-author of the study, said: “Individual trees with low wood density have the greatest risk of dying, but such properties at species level do not explain the extreme mortality experienced by these forests. in its entirety.

“On the contrary, damage from climatic extremes, particularly wind and drought, places exceptional stress on trees in the southern Amazon.”

Lead author Dr Simone Matias Reis of UNEMAT said: “Crown breaking greatly increases the risk of tree death. Once broken, the risk of death is much higher, especially when much of the tree canopy is broken.

“The growth of broken trees is also affected, as these trees lose their ability to photosynthesize and thus absorb less carbon, which increases the risk of death.”

The researchers believe that the significant impact of climatic water deficits on mortality is of particular concern due to climate modeling studies predicting more intense and prolonged seasonality for the Amazon jungle, which could lead to high and potentially unprecedented mortality rates. for trees in the southern edge region.

Professor Beatriz S. Marimon, supervisor of the study at UNEMAT, said: “This region already has the highest mortality rates of the entire Amazon region, so it is essential to determine why trees are dying here in so many.

“Our research findings provide a window into what the future of large parts of the Amazon could look like if climate change and fragmentation continue to damage the Amazon rainforest.”

Co-author Professor Ben Hur Marimon of UNEMAT said: “The cumulative effects of tree failure may be one of the most important elements of the Amazonian tipping point, beyond which the forest can no longer recover.”

Scientists discover how and why Amazon trees are dying

More information:
Simone M. Reis et al, Climate and crown damage drive tree mortality in southern Amazonian edge forests, Journal of Ecology (2022). DOI: 10.1111/1365-2745.13849

Provided by the University of Leeds

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