Study Overturns Theory That Tall Trees Struggle to Move Water Upward

A long-held idea in plant science holds that as trees grow taller, gravity and the sheer length of their internal plumbing make it progressively harder to draw water from roots to leaves — capping growth and leaving big trees more exposed to drought. Research led by the University of Exeter and Cardiff University, published in Science, contradicts that assumption for the world’s tallest tropical trees. Studying Dipterocarps ranging from 7 to 71 metres in Malaysian Borneo, the team found the trees make internal adjustments that fully offset the difficulty of lifting water to the crown.

The compensations are structural: water-conducting vessels widen closer to the ground, and upper leaves are adapted to tolerate more water stress before wilting. Measurements of trunk growth before, during, and after the severe 2023–2024 El Niño drought showed the tallest trees suffered no height-related loss in growth or hydraulic function relative to shorter neighbors. In other words, their water systems appear precisely tuned to their scale rather than strained by it.

The finding matters beyond botany. The tallest 1% of trees store more than half of a forest’s above-ground carbon, and some climate models assume these giants face elevated drought-mortality risk because of weaker hydraulics. This work suggests that assumption may be wrong, implying greater drought resilience in exactly the trees that lock up the most carbon — a point the authors argue strengthens the case for protecting these forests. They caution that other tall-tree species still need testing before the result can be generalized.