Height does not impair the hydraulic system of the tallest tropical Dipterocarp trees

Bittencourt, Paulo ORCID: https://orcid.org/0000-0002-1618-9077, Scheire, Arne, Jotan, Palasiah, Lourenço, Jehova, Banin, Lindsay F., Suis, Mohd Aminur Faiz bin, Burslem, David F. R. P., Christoffersen, Bradley, Coomes, David, Groenendijk, Peter, Jansen, Steven, Jucker, Tommaso, Matula, Radim, Mencuccini, Maurizio, Oliveira, Rafael, Plichta, Roman, Nilus, Reuben, Robert, Rolando, Svátek, Martin and Rowland, Lucy 2026. Height does not impair the hydraulic system of the tallest tropical Dipterocarp trees. Science 393 (6806) , pp. 60-64. 10.1126/science.aea9013

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Abstract

INTRODUCTION More than half of the carbon in forest ecosystems is stored in only 1% of the tallest trees. These tall trees are predicted to be more likely to suffer drought-induced damage under future drier climates. As a tree becomes taller, the distance from root to leaf increases, increasing the resistance to water flow. In addition, the greater effects of gravity with height reduce leaf water potential, a key metric of leaf water status. Despite the potential of trees to adjust key traits to minimize these effects, it is still hypothesized that the effects of gravity and path length reduce how effectively a tall tree can keep its canopy hydrated and resist the impact of drought events. However, to date very little data exist that can directly test whether the water transport systems of tall trees are negatively affected by tree height. RATIONALE To study the effects of tree height on the plant water transport system, we studied trees from the tallest angiosperm family in the world, Dipterocarpaceae, which dominates the rain forests of Southeast Asia. We sampled 38 trees, from five species, ranging from 7.1 to 71 m in height. Measuring a suite of traits related to tree hydraulic function in addition to growth rates before, during, and after a strong drought, we sought to determine whether tall trees show systematic drops in water supply to their canopy, which could increase their vulnerability to drought and reduce their growth. RESULTS We show that adjustments to woody vessel anatomy, including wider water-transporting vessels at the base of taller trees, compensated for the increased resistance to water flow associated with longer path lengths. Similarly, although leaf water potential did decline as the effects of gravity increased with height, so did the capacity of leaves to tolerate lower leaf water potentials, meaning that there were no negative impacts on leaf functioning. In addition, we found that the vulnerability of woody tissue to drought-induced embolism, a process that blocks the flow of water from root to leaves and makes them more prone to drought-induced damage, was not related to tree height. This result was further supported by no observed height-related declines in growth rate during a severe drought event. CONCLUSION We demonstrate that height does not impair the water transport system of the world’s tallest tropical tree species, increasing their hydraulic vulnerability or causing declining growth rates during drought as they grow taller. As these trees grow taller, their woody anatomy and leaf functioning adjust to fully compensate for the effects of path length and gravity. Our study suggests that changes in a tree’s vulnerability to drought-induced embolism may be more related to canopy microclimate and shading than to height. Consequently, the widely adopted assumption that drought vulnerability increases with tree size needs to be more widely verified, as does the assumption that the negative effects of height on the plant water transport system can explain the elevated mortality in taller trees.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Additional Information:	RRS policy applied
Publisher:	American Association for the Advancement of Science
ISSN:	0036-8075
Date of First Compliant Deposit:	16 July 2026
Date of Acceptance:	16 April 2026
Last Modified:	03 Aug 2026 12:15
URI:	https://orca.cardiff.ac.uk/id/eprint/188008

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