In a groundbreaking study published on September 25, 2025, in Nature Plants, a consortium of over ninety scientists from more than sixty universities worldwide revealed that the average size of trees across the Amazon Basin has been increasing steadily at a rate of approximately 3.2% each decade over the past thirty years. This remarkable finding emphasizes the adaptive response of these tropical forests to rising atmospheric carbon dioxide levels, underscoring the dynamic and resilient nature of one of Earth’s most critical ecosystems.
The research team meticulously analyzed data from 188 long-term permanent forest plots distributed throughout the Amazon rainforest. This extensive ground-based inventory was conducted under the auspices of the RAINFOR (Amazon Forest Inventory Network) initiative, which has been tracking individual tree metrics such as diameter at breast height (DBH), species identity, growth rates, and mortality over multiple decades. The investigators’ ability to revisit and measure each tree multiple times allowed the capture of nuanced changes in forest structure, providing unprecedented insights into the growth patterns and demographic shifts within this globally significant biome.
Integral to the study’s impact is the revelation that not only the largest canopy giants but also smaller tree cohorts have exhibited significant growth over the past three decades. This suggests a pervasive biological response enhanced by CO2 fertilization, a phenomenon whereby elevated atmospheric carbon dioxide concentrations enhance photosynthetic capacity and water-use efficiency in plants, leading to accelerated biomass accumulation. While climate change and habitat fragmentation pose severe threats to rainforest integrity, these findings show that in relatively intact forest areas, carbon fertilization is currently fostering a net increase in tree size.
Professor Beatriz Marimon, who spearheaded data collection efforts in the southern Amazon, highlights the paradox this presents: “While there is constant discourse on the destruction facing the Amazon due to deforestation and climate extremes, our data reveal an ecosystem actively thriving in many undisturbed areas. The upward trend in tree size, including among massive, centuries-old specimens, is reassuring evidence of the forest’s resilience amid ongoing environmental pressures.”
Of particular significance is the role of these large trees as carbon sinks. According to Dr. Adriane Esquivel-Muelbert, formerly affiliated with the University of Birmingham and currently at the University of Cambridge, “Large trees disproportionately contribute to carbon sequestration, making their growth vital to the global carbon cycle. This research confirms that despite climate volatility, CO2 enrichment continues to stimulate growth and maintain the Amazon’s critical function in mitigating anthropogenic climate change.” Her comment underscores how large tropical trees operate as keystones in maintaining atmospheric carbon balance.
Contrastingly, Dr. Rebecca Banbury Morgan from the University of Bristol draws attention to the irreplaceability of mature forests compared to reforested or secondary-growth areas. “Old-growth tropical forests represent centuries of accumulated biomass and biodiversity. Merely planting new trees cannot replicate these complex carbon reservoirs or ecosystem services. Our study therefore amplifies the urgent need to halt deforestation and preserve mature forest structure to sustain these carbon sinks.”
The study also contributes a new dimension to understanding forest dynamics under climate change by revealing alterations in the forest’s size structure. The largest trees have increasingly dominated competition for light and nutrients, altering ecological interactions within the canopy and potentially affecting species composition. Professor Tim Baker of the University of Leeds, a joint senior author, notes, “The Amazon is not static—it’s actively changing. This size increase across all tree classes indicates fundamental shifts in forest composition and carbon storage capacity rarely captured before.”
This robust response, however, is not without caveats. The researchers caution that the synergistic effects of ongoing deforestation and climate pressures remain a formidable threat to the sustainability of these large tree populations. Professor Oliver Phillips from the University of Leeds, an expert in tropical ecology, stresses the importance of connectivity within the Amazonian ecosystem to preserve seed dispersal networks and genetic flow essential for the survival of these majestic giants. “Connectivity is mission-critical; fragmentation fragments these lifelines, imperiling the future health and resilience of the forest.”
Scientific consensus recognizes the abundance of mature trees as crucial to maintaining global climatic stability. The Amazon, often described as “the lungs of the planet,” sequesters billions of tons of carbon annually. By combining comprehensive field measurements with atmospheric science, this study provides compelling evidence that the heightened levels of anthropogenic CO2, while responsible for climate challenges, concurrently reinforce the carbon uptake capability of intact Amazonian forests.
This nuanced revelation adds a critical layer to the broader climate discourse, highlighting the vital role of conserving intact tropical ecosystems not only for biodiversity but as a frontline defense against climate change. The findings anticipate crucial discussions at the upcoming COP30 climate conference in Brazil, where emissions reduction commitments and conservation strategies will be at the forefront.
Incorporating state-of-the-art techniques, the RAINFOR network protocol classified trees by species and repeatedly measured individual growth metrics, providing statistically robust evidence of these trends rather than relying solely on remote sensing or modeling. This field-based experimental approach affirms the continued scientific value of hands-on ecological monitoring in capturing long-term ecological processes in a changing world.
Despite the positive news about tree growth and carbon uptake, researchers unanimously emphasize that such benefits hinge on the maintenance of large, connected forest landscapes. Initiatives to curb deforestation and promote sustainable land use in the Amazon Basin remain paramount, as unchecked forest loss would negate the natural gains observed and exacerbate climate instability worldwide.
This study, therefore, embodies a beacon of hope amid environmental concerns. It illustrates how the Amazon rainforest, often perceived as vulnerable and faltering, exhibits an intrinsic capacity for resilience and adaptation, buoyed by scientific evidence of thriving tree growth in intact regions under rising CO2. However, the balance is delicately poised and contingent on robust conservation efforts and international cooperation to safeguard this irreplaceable global resource.
Subject of Research: Not applicable
Article Title: Increasing tree size across Amazonia
News Publication Date: 25-Sep-2025
Image Credits: Pauline Kindler (Scientists in Colombia measuring a giant Ceiba tree), Adriane Esquivel Muelbert (View of the rainforest canopy)
Keywords: Climate change, Forests, Rainforests, Tropical forests, Trees, Atmospheric carbon dioxide, Anthropogenic carbon dioxide, Carbon emissions
