Giant trees withstand drought better than expected

The Kapur ( Dryobalanops lanceolata ) and the White Seraya ( Parashorea malaanonan ) are two of the tallest trees in the world. They can exceed 70 meters in height and inhabit the tropical rainforests of Asia. With the increasing frequency and severity of droughts, the scientific community is wondering if these giants might be at risk. Common sense tells us that it must be very difficult to transport water to a height of 70 meters, and that drought poses a threat to their hydraulic system. However, new research published today in Science reveals that, contrary to what was previously thought, they have no difficulty transporting water to their highest branches, and this ability makes them just as resistant to drought as shorter specimens of the same species.

According to the team, this is good news because the tallest 1% of trees store more than half of the carbon accumulated in tropical forest vegetation and because it provides key information on how tree height influences drought events. The study was led by University of Exeter researchers Lucy Rowland and Paulo Bittencourt, who is also a researcher at Cardiff University, and involved various institutions, including CREAF.

Until now it was believed that taller trees were not as efficient at transporting water to the highest branches and that, therefore, they were more vulnerable to droughts than their shorter counterparts, but the results call this scientific theory into question.

In the tallest trees, the vascular system, through which water circulates, widens as it descends from the canopy to the base of the trunk, allowing the liquid to flow more easily. Furthermore, their leaves take longer to dehydrate and can wait longer for water to arrive . “They achieve this by modifying the concentration of dissolved compounds in their cells, such as salts and sugars, to retain more water,” explains Mencuccini. This mechanism is very useful during droughts because they can photosynthesize for a longer period before the effects become apparent.

To conduct the study, the team analyzed 38 trees from five species typical of the rainforests of Malaysian Borneo and belonging to the Dipterocarpaceae family. The trees ranged in height from 7 to 71 meters. The researchers evaluated various characteristics related to water transport and drought tolerance. They also studied trunk growth rates before, during, and after the drought episode associated with the 2023-2024 El Niño phenomenon. “When comparing the shortest trees with the tallest, we found that both groups responded very similarly to the drought, regardless of their height,” Menccuccini added.

Giant trees are rare, but essential. On the one hand, they harbor a great deal of biodiversity within their branches, and on the other, they play an important role in regulating the global climate, since, being so large, they accumulate a great deal of carbon in their structure—trunk, branches, and leaves . “If they die, they stop storing carbon, and some of the CO₂ retained in their wood ends up returning to the atmosphere,” the researcher explains.

The resilience reflected in the study suggests that the risk of drought death for larger trees may be overestimated, as it does not account for their ability to compensate for the effects of height through hydraulic adaptations. “So these results could contribute to improving predictions about how tropical forests will respond to future droughts,” the researcher explains.

The strategies identified in these giant trees could be common in other tree species that reach great heights, including Mediterranean forests. “Although it is still unclear whether the leaves function in the same way, we will need to expand the research to include more types of forests,” Mencuccini concludes.

The research team included the Sabah Forestry Department (Malaysia), the UK Centre for Ecology and Hydrology, and the University of Aberdeen, as well as institutions in the Czech Republic, Spain, Brazil, and the United States. The study was funded by the UK's Natural Environment Research Council .

Scientific article reference: Bittencourt, P., Scheire, A., Jotan, P., Lourenço-Junior, J., Banin, LF, bin Suis, MAF, Burslem, DFRP, Christoffersen, B., Coomes, D., Groenendijk, P., Jansen, S., Jucker, T., Matula, R., Mencuccini, M., Oliveira, R., Plichta, R., Nilus, R., Robert, R., Svátek, M. & Rowland, L. (2026). Height does not impair the hydraulic system of the tallest tropical Dipterocarp trees. Science. DOI: https://doi.org/10.1126/science.aea9013