Trees across the Amazon are getting bigger, according to new research published in Nature Plants. The study reveals that the average tree size has increased by 3.2% each decade, a trend linked to rising levels of atmospheric carbon dioxide.
The findings come from an international network of scientists who monitored tree growth in 188 permanent plots across the Amazon for more than 30 years. The collaboration involves over 60 universities from South America, the UK, and beyond, including the Universities of Birmingham, Bristol, and Leeds.
Professor Beatriz Marimon of Universidade do Mato Grosso, who coordinated much of the Brazilian data, said: “This is a good news story. We regularly hear how climate change and fragmentation threaten Amazonian forests. But meanwhile, the trees in intact forests have grown bigger; even the largest trees have continued to thrive despite these threats.”
Bigger trees, stronger carbon sinks
The study found that both small and large trees have grown in size, consistent with benefiting from CO2 fertilisation. Large trees play a particularly vital role in absorbing carbon dioxide, acting as powerful natural carbon sinks.
Dr Adriane Esquivel-Muelbert of the University of Cambridge, joint lead author of the study, explained:
“Despite concerns that climate change may undermine the Amazon’s ability to act as a carbon sink, we see that CO2 continues to stimulate growth. This shows the remarkable resilience of these forests, at least for now.”
Old forests vs new plantations
Dr Rebecca Banbury Morgan of the University of Bristol, another lead author, stressed that deforestation undermines these gains:
“Large tropical trees are hundreds of years old. We can’t simply plant new trees and expect them to deliver the same carbon and biodiversity benefits as old, natural forests.”
Previous research has already shown that intact Amazon forests store more carbon today than in the past. This latest study goes further, confirming that the increase applies to trees of all sizes, shifting the structure of the entire forest.
A warning for the future
As the biggest trees grow, they dominate competition for light and resources. But their survival depends on keeping the Amazon ecosystem connected.
Professor Oliver Phillips of the University of Leeds noted:
“What happens to big trees – including how they deal with climate threats and manage to disperse their seeds – is mission-critical. The only way the giants will stay healthy is if the Amazon ecosystem stays connected. Deforestation is a huge threat-multiplier and will kill them if we let it.”
Why this matters for COP30
The study’s release comes just weeks before COP30 in Brazil, where global leaders will debate how to accelerate action on climate change. The findings highlight the resilience of the Amazon, but also underline that protecting existing forests is far more effective than replanting alone.