The fattening forest: trees of the Amazon are getting bigger 

Average tree size across the Amazon has increased by 3.2% every decade consistent with a response to rising carbon dioxide levels, a new study suggests.  

 The new research published today (25 Sep) in Nature Plants by a global team of tropical forest scientists shows that the average size of trees in Amazon forests has increased over recent decades. The team of almost a hundred researchers monitored the size of trees in 188 permanent plots and discovered that the increase has continued for at least 30 years.  

The study is the result of an international partnership of more than 60 universities in South America, the UK and beyond – including the Universities of Birmingham, Bristol, and Leeds. 

 Co-author of the study Professor Beatriz Marimon, from Universidade do Mato Grosso, who coordinated much of the Brazilian data collection in southern Amazonia, commented: “This is a good news story. We regularly hear how climate change and fragmentation is threatening Amazonian forests. But meanwhile the trees in intact forests have grown bigger; even the largest trees have continued to thrive despite these threats.”  

 The study found that both large and smaller trees have increased in size, consistent with benefitting from fertilisation by increased atmospheric carbon dioxide.   

Joint lead author of the RAINFOR paper Dr Adriane Esquivel-Muelbert, from the University of Cambridge – who led the research whilst at the Universities of Birmingham and Leeds – commented: “Ahead of COP30 in Brazil later this year, these results underscore just how important tropical rainforests are in our ongoing efforts to mitigate against man-made climate change.   

 “Large trees are hugely beneficial for absorbing CO2 from the atmosphere and this study confirms that. Despite concerns that climate change may negatively impact trees in the Amazon and undermine the carbon sink effect, the effect of CO2 in stimulating growth is still there. This shows the remarkable resilience of these forests, at least for now.”  

 Dr Rebecca Banbury Morgan from the University of Bristol and joint lead author added: “Our paper also highlights how destructive Amazon deforestation really is. Large tropical trees are hundreds of years old. We can’t simply plant new trees and expect them to confer anything like the kinds of carbon or biodiversity benefits that the old, natural forest is providing.”  

 According to previous research by the RAINFOR network, the Amazon Forest plays a key role in taking up carbon which would otherwise be in the atmosphere.  

 “We knew that the total amount of carbon stored in the trees of intact Amazonian forests has increased. What this new study shows is that all sizes of tree have grown larger over the same period – the whole forest has changed.” added Professor Tim Baker from the University of Leeds, joint senior author of the study.  

The study is the first of its kind to measure how increases in CO2 have systematically changed the tree size structure of Amazon forests. The team noted that as the biggest trees have grown larger, they have managed to increasingly dominate competition for resources.   

The authors point out the new research has other implications too. According to Professor Oliver Phillips of the University of Leeds: “What happens to big trees – including how they deal with increasing climate threats and manage to disperse their seeds – is now 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.”   

ENDS  

For media enquiries please contact:  

• University of Birmingham - pressoffice@contacts.bham.ac.uk or +44 (0)121 414 2772.   

• University of Bristol - press-office@bristol.ac.uk  

• University of Leeds - pressoffice@leeds.ac.uk  

PHOTO CAPTIONS 

• Scientists in Colombia measuring a giant Ceiba tree (Credit: Pauline Kindler) 

• View of the rainforest canopy (Credit: Adriane Esquivel Muelbert) 

Notes to editor:   

• The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, educators and more than 8,000 international students from over 150 countries.     

• The University is leading research to help mitigate and adapt to the risks and impacts associated with climate change - working with industry, academic and policy partners across the globe to accelerate progress on the Sustainable Development Goals (SDGs) towards the 2030 Agenda. Birmingham has been awarded UNFCCC Observer Status, which means its researchers are able to contribute to the vital discussions taking place at COP30.     

• Only careful, long-term measurements on the ground can tell us how intact forests are really changing on the inside. The RAINFOR Amazon Forest Inventory Network team of 95 researchers measured mature forest plots for more than 30 years, during which carbon dioxide concentrations have risen by nearly a fifth. In each plot the diameter of each tree was measured, the species identified, and investigators returned many times to revisit each tree and learn its fate. RAINFOR’s long-term aim is to understand the dynamics of Amazon ecosystems. For this, team members have developed a framework for the systematic monitoring of forests from the ground-up centred on plots that track the life and death of each tree and species, and including soil and plant traits, as well as intensive monitoring of carbon cycle processes at some sites. RAINFOR partners across the nine nations of the Amazon share a commitment to sustain forest monitoring and help develop new generations of Amazon ecologists.    

About the University of Bristol  

• The University is ranked within the top ten universities in the UK and 51st in the world (QS World University Rankings 2026); it is also ranked among the top five institutions in the UK for its research, according to analysis of the Research Excellence Framework (REF) 2021; and is the 5th most targeted university by top UK employers.  

• The University was founded in 1876 and was granted its Royal Charter in 1909.  It was the first university in England to admit women on the same basis as men.   The University is a major force in the economic, social and cultural life of Bristol and the region, but is also a significant player on the world stage. It has over 20,000 undergraduates and over 7,000 postgraduate students from more than 150 countries, and its research links span the globe.