The giant trees of tropical forests are important allies in the fight against climate change due to their ability to store carbon, yet they are still poorly understood by science. However, a study published July 2, 2026, in the journal Science reveals a crucial survival mechanism: these trees, which exceed 70 meters in height, have no difficulty transporting water to their tops and are no more vulnerable than smaller trees.
They have developed internal adaptations that compensate for the challenges of transporting water to the highest branches. Furthermore, tests conducted during severe droughts showed that they did not experience a more pronounced decline in growth compared to smaller trees. This contradicts the hypothesis that very tall trees would be more susceptible to water stress.
To date, the scientific literature suggests that as trees grow taller, their ability to move water upward is impaired by the greater distance between roots and leaves, as well as by the effects of gravity. This would reduce photosynthesis, limit growth, and increase vulnerability to drought.
The research found that adjustments to the xylem conduits (microscopic "tubes" that the plant uses to transport water and nutrients to the leaves) – which increase in diameter as the tree grows taller – compensate for the increased resistance to water flow along the way. In practice, it's as if a larger hose were needed to carry water farther. These complex adaptations reduce the likelihood of water transport failure when the plant is in drought conditions.
In the case of leaves, gravity forces them to function with lower hydration, or a more negative water potential. This causes them to wilt and close their stomata, or microscopic "pores," earlier, thereby reducing their photosynthesis. However, the study shows that these trees increase their tolerance to these conditions without compromising their function.
These findings advance our understanding of the biology of giant trees. They help explain how these trees overcome physical and physiological limitations to transport water and continue growing. The findings also enhance our understanding of the role of forests in climate change. Additionally, they provide evidence to guide conservation efforts aimed at maintaining the balance of the carbon cycle, rainfall, and biodiversity.
"There's little data on how a plant's hydraulic functions change as it grows. It's generally accepted that larger trees have difficulty transporting water and are therefore more likely to die during droughts. We were very surprised by the results of our study, which showed that they have an internal adjustment mechanism," Paulo Bittencourt , the corresponding author of the article and a professor at the School of Earth and Environmental Sciences at Cardiff University (United Kingdom), as well as a collaborating researcher at the Institute of Biology at the State University of Campinas (IB-UNICAMP) in Brazil, tells Agência FAPESP.
According to the ecologist, 1% of the largest trees on the planet store more than half of the carbon in tropical forest ecosystems. They also contribute to the rainfall cycle through evapotranspiration.
The study was supported through a Young Investigator grant from FAPESP, awarded to biologist Peter Groenendijk , who is a co-author of the article alongside Rafael Oliveira . Both are from the Center for Integrative Ecology at IB-UNICAMP.
'Climbing the forest'
To conduct the study, which took more than two years, the group used a sample of 38 Dipterocarpaceae trees representing five species located in the Kabili-Sepilok Forest Reserve in Malaysia on the Asian island of Borneo. The reserve is world-renowned for its conservation centers, including the world's first center dedicated to orangutan rehabilitation.
These trees range from 7.1 to 71 meters in height, equivalent to a building with more than 20 stories, and are considered the tallest flowering trees in the tropics.
The fieldwork was made possible by the contribution of climbers trained by Jamiludding Jami, an arborist affiliated with the Southeast Asian Rainforest Research Partnership ( SEARPP ). In 2018, Jami climbed and measured a 100.8-meter-tall dipterocarp (yellow meranti, Shorea faguetiana), considered the tallest tropical tree found to date.
"Climbing a tree over 70 meters tall is a very special job that very few people in the world do. These are people who, in the middle of the forest, can thread a rope through a tree as tall as a 20- to 30-story building, climb it, and collect branches, for example. Some collections had to be done at night, without sunlight. It isn't just about knowing how to thread the rope and being physically fit. You have to check for wasp nests, know if a branch is suitable, if the wood is strong – it isn't a trivial matter," says Bittencourt.
This expertise was shared with climbers in the Brazilian Amazon – specifically, members of riverside communities in the state of Amapá. After receiving training, these climbers helped collect materials for similar research in the Amazon rainforest. Some of these results are expected to be released by the end of 2026.
For several years, this group of scientists has been studying Amazonian giants in the Tumucumaque Mountains National Park and the Amapá National Forest regions, where several expeditions have already taken place. The project aims to understand how the Amazon rainforest physiologically responds to climate change. It is led by British ecologist Lucy Rowland of the University of Exeter. Bittencourt worked directly with Rowland while at the institution, and Rowland is also an author of the study published in Science.
Estimates from another study led by Robson Borges de Lima of the State University of Amapá, in which Bittencourt and Groenendijk participated, indicate that the Brazilian Amazon has approximately 55.5 million giant trees. However, their geographic distribution is uneven. Just 1% of the forest area accounts for 14% of these trees, half of which are located in approximately 11% of the biome. The trees are mainly found in Roraima state and the Guiana Shield (a geological formation that includes part of Amapá), where water availability is high (read the article here: https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.70634# ).
Impacts of climate change
To analyze how dipterocarps react to water stress, the researchers measured their trunk growth rates before, during, and after the severe drought associated with the 2023–2024 El Niño event. The 2023–2024 El Niño, a climate phenomenon characterized by abnormal warming of the surface waters of the equatorial Pacific Ocean, was considered one of the five most intense ever recorded. Classified at the threshold of the "very strong" category, it raised temperatures by about 2 °C above average, impacting the climate of several countries in different ways.
In the study, no decline in growth rate associated with tree height was observed during the severe drought. In other words, the tallest trees were affected just as much as the shorter ones, experiencing similar impacts from climate change.
"Our findings demonstrate that the hydraulic systems of very tall dipterocarps have evolved to be perfectly adapted to their height and should not suffer more than smaller trees exposed to the same drought conditions," Rowland states in a press release.
In this regard, the research suggests that differences in the ability of trees to prevent air bubbles (embolisms) that disrupt internal water circulation during droughts may be more closely related to canopy microclimate and shading than to height.
For Oliveira, the results highlight the need for a better understanding of the mechanisms that determine tree mortality during extreme droughts. "Rather than assuming that height alone increases hydraulic vulnerability, the findings suggest that other physiological and anatomical mechanisms may be equally or more important in explaining the survival of these trees in the face of climate change. This new perspective can help us develop more realistic models of how forests function and respond to increasingly dry climates," Oliveira tells Agência FAPESP.
Groenendijk emphasizes the importance of understanding the growth rates of these species. "Understanding how old these giants get, how they grow, and how they behave in the face of climate variability are crucial questions we're trying to answer using automated sensors and growth ring analysis," he added.
In Brazil, an international group of scientists is collecting data at the Adolfo Ducke Forest Reserve in Manaus, in the state of Amazonas, to quantify and map the causes and factors leading to the death of tall tropical trees. The "Giant Project" is being developed by members of the Cary Institute of Ecosystem Studies in Millbrook in the United States in cooperation with Brazil's National Institute for Amazonian Research (INPA).
Oliveira points out that a mechanism compensating for drought resistance is likely linked to the ability of the uppermost leaves to absorb dew and fog. "Previous research we've conducted has shown that atmospheric sources can be important for maintaining hydration in plants in general, even those with very large leaves," he concludes.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe
