Towering trees more than 200 feet tall may not be as vulnerable to drought as scientists thought, new study reveals how Southeast Asia’s dipterocarps efficiently move water

A 187-foot-tall dipterocarp tree

For decades, scientists believed that the tallest trees faced one of nature’s toughest challenges: Getting water from their roots to leaves hundreds of feet above the ground. Now, a study of towering trees in Southeast Asia suggests some of the world’s tallest flowering plants have evolved specialised systems to overcome that problem.Researchers studying dipterocarps in Malaysia found that these giant rainforest trees have developed ways to move water efficiently through their trunks, allowing them to cope with the physical demands of extreme height. The findings challenge the long-held idea that taller trees are more vulnerable to drought.The study was published in the journal Science on July 2. It focused on five species of dipterocarps in the Kabili-Sepilok Forest Reserve on the island of Borneo. Scientists say the discovery could influence how forests are understood in a changing climate, as the tallest 1 per cent of trees hold more than half of all above-ground carbon stored in forests.“These trees are rare and important, and existing predictions suggest a weaker hydraulic system places them at higher risk of dying due to drought,” says Paulo Bittencourt, the study’s lead author and a forest ecologist at Cardiff University in Wales, in a statement.They added: “That prediction is included in some models of climate change impacts, and our study suggests this may not be correct. More research is now needed to investigate the hydraulic systems and drought resilience of other tall trees.”

Studying trees taller than 20-storey buildings

The research team spent three months in 2022 collecting samples from 38 dipterocarp trees ranging from around 25 feet to 233 feet tall. The work involved gathering branches, leaves and trunk samples from trees that can rise as high as a 20- to 30-storey building.The samples had to be collected from the upper parts of the trees, so the scientists worked with trained climbers who scaled the massive trunks and reached branches far above the forest floor.“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,” Bittencourt says in a different statement.They added: “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.”The collected material was analysed for features linked to water movement inside trees. Scientists examined the structure of the xylem, the plant tissue responsible for transporting water and nutrients from roots to leaves.

Tall trees adapted their internal plumbing

The researchers found that taller dipterocarps have wider xylem vessels near the base of their trunks. These wider channels help reduce the resistance water faces as it travels upwards against gravity.The leaves growing near the tops of these trees also showed an ability to tolerate drier conditions without losing their function. Together, these adaptations allow the trees to maintain water transport despite their enormous height.The findings do not mean that all tall trees are protected from drought. Different species have different biological systems and face different environmental pressures. But the study suggests that height alone may not determine whether a tree survives dry conditions.To examine how these trees responded to water shortages, the researchers also measured trunk growth before, during and after an El Niño-related drought between 2023 and 2024. They found that taller trees did not show a greater decline in growth compared with shorter trees during the drought.

The world’s tallest trees face similar challenges

The results add to a growing understanding that tree size and drought survival are more complicated than previously thought.Adrian Das, a forest ecologist at the US Geological Survey who was not involved in the research, said the findings matched patterns seen during droughts in the Sierra Nevada mountains. “The relationship between size and mortality during drought varied by species,” he explains to Mona Patterson at Science.In those forests, factors such as vulnerability to bark beetles appeared to play a larger role in tree deaths than height alone.The research also offers a different view of how trees respond to their surroundings. Julieta Rosell, a functional ecologist at the National Autonomous University of Mexico who was not involved in the study, tells Fechi Inyama at Science News that the findings prompt us to reconsider the nature of trees.“They’re doing things all the time, making changes in their anatomy all the time,” she says to the outlet. “And that gives a different perspective to trees, because they seem so quiet.”

Giant trees around the world reveal different survival strategies

The study of Southeast Asia’s dipterocarps adds to research on other giant tree species that have developed their own ways of surviving extreme conditions.The General Sherman Tree in California’s Sequoia National Park is the world’s largest known living single-stem tree by volume. The giant sequoia stands about 83.8 metres tall and contains an estimated 1,487 cubic metres of trunk volume. Although it is not the tallest tree on Earth, its enormous size has made it one of the most studied trees in the world.Estimated to be between 2,200 and 2,700 years old, the General Sherman Tree survives partly because of the thick, fire-resistant bark of giant sequoias. Older trees can develop bark more than 90 centimetres thick. Fire also helps these forests by releasing seeds from cones and reducing competing vegetation.

The Largest Living Tree: The General Sherman Giant Sequoia

The tallest trees known today belong to another species: The coast redwood. Found along coastal areas of northern California and southern Oregon, these trees can reach heights far beyond most other plants.The tallest known living tree is Hyperion, a coast redwood discovered in 2006 in Redwood National and State Parks. It measures about 115.9 metres, although its exact location is kept private to protect it from damage caused by too many visitors.Coast redwoods benefit from their cool, wet environment near the Pacific Ocean. Coastal fog provides extra moisture during dry periods, while their biological adaptations help them move water through trunks that can rise more than 100 metres into the air.Some historical giants, such as the Dyerville Giant, also belonged to the coast redwood species. Before it fell in 1991, the tree measured about 113 metres tall.Another tree capable of extreme height is the mountain ash of Australia. Some past specimens grew beyond 100 metres, although no living mountain ash currently reaches the height of the tallest coast redwoods.Scientists continue to study these giant trees because their survival offers clues about how forests may respond to future climate pressures. The new dipterocarp research suggests that some of Earth’s tallest trees may have more control over their water systems than scientists once believed.