Going against gravity

In a recent paper published in Science, Paulo Bittencourt at Cardiff University and colleagues addressed this question in five dipterocarp species, members of the tallest angiosperm tree family and dominant components of rainforests in Southeast Asia. After measuring a variety of hydraulic-related traits at multiple positions in different trees ranging from 7.7–71 m tall and monitoring trunk growth before, during and after the severe 2023–2024 El Niño drought, the researchers found that water-conducting vessels widened from the branch tips towards the trunk rapidly enough to offset the resistance imposed by longer transport pathways. Although upper-crown leaf water potential decreased with height, these changes were accompanied by increased leaf tolerance. As a result, taller trees experienced no greater reduction in growth than did shorter trees during and after the drought.

This study challenges the assumption that height places the hydraulic systems of giant trees at greater risk. Instead, the tallest dipterocarps appear to compensate for both gravity and long transport distances through coordinated adjustments in their woody anatomy and leaf functions. The findings also suggest that the conditions of the canopy may shape hydraulic traits more strongly than tree height alone.

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