BORNEO — Researchers published findings on tree drought biology in the journal Science on July 2, revealing that tall dipterocarp trees in Borneo maintained water transport during drought as effectively as shorter trees. This study challenges the assumption that greater height makes trees more vulnerable to drought.

The research, conducted in Malaysia's Kabili Sepilok Forest Reserve, indicates that the water transport systems of these dipterocarp trees were not more impaired than those of shorter trees during a drought. The study covered an intense drought period from 2023 to 2024 and found no height-related declines in growth rate among the sampled trees.

The research team collaborated with professional climbers to collect leaf, trunk, and branch materials from different heights throughout the day. They set up instruments before sunrise to measure water potential in the trees. Researchers measured stem diameters at various heights on the trees and also assessed 25 traits related to tree water transport.

The study included 38 trees from five species, ranging in height from 7.7 meters to 71 meters, with the tallest sampled tree exceeding 70 meters. Taller trees consistently exhibited larger xylem widths at their base on average. Higher leaves also adjusted their dehydration limit to accommodate reduced water transport.

Julieta Rosell, a functional ecologist at the National Autonomous University of Mexico in Mexico City who was not involved in the research, commented on the novelty of the approach. "This was never done before," Rosell said, referring to the detailed measurements. "They're doing things all the time, making changes in their anatomy all the time," she added. "And that gives a different perspective to trees because they seem so quiet."

Arne Scheire, a plant functional ecologist at the Southeast Asia Rainforest Research Partnership in Kota Kinabalu, Malaysia, who was previously at the University of Exeter in England, said that dipterocarp trees may offer a long-term solution for carbon sequestration. "They may be a good long-term spot to sequester carbon in Southeast Asia," Scheire said. The study does not confirm that these findings apply to all tree families.

Why It Matters

This research re-evaluates long-held assumptions about how tree height affects drought vulnerability, specifically for dipterocarp trees. Understanding how these rainforest trees adapt to drought conditions is relevant as global climate patterns change. The findings suggest that these tall trees, which are prominent in Borneo's rainforests, possess adaptive mechanisms that allow them to maintain water transport during periods of water scarcity.

The study provides specific insights into the anatomical and physiological adaptations, such as wider xylem at the base of taller trees and dehydration limit adjustments in higher leaves, that contribute to this resilience. This information is important for assessing the role of these trees in carbon sequestration in Southeast Asia and their potential resilience to future drought events.