The world’s tallest tropical trees, which grow on the island of Borneo and reach heights of up to 100 meters, are no more susceptible to water transport failure during the dry season than shorter trees. This is the conclusion of a new study published in the prestigious international scientific journal Science, to which scientists from Mendel University in Brno and the Czech University of Life Sciences Prague contributed significantly. The research refutes the previous hypothesis that their hydraulic system fails during increasingly frequent dry spells. These giant trees play an irreplaceable role in carbon sequestration, biomass production, microclimate regulation, and the promotion of biodiversity.
The tallest tropical trees, which belong to the Dipterocarpaceae family, dominate the intact rainforests of Borneo and form the backbone of Southeast Asia’s forest ecosystems. Until now, it was assumed that their extraordinary height posed a significant disadvantage during dry seasons. However, a new study shows that, thanks to anatomical adaptations, these trees are able to ensure reliable water transport all the way to the tops of their crowns even during periods of low rainfall.
The research was conducted by scientists from Mendel University in Brno (MENDELU) and the Czech University of Life Sciences in Prague (ČZU), in collaboration with experts from the United Kingdom, Malaysia, Germany, Spain, Brazil, and the United States.
The researchers monitored trees of various sizes in the Malaysian part of Borneo, in the state of Sabah. From the base of the trunk to the tree crowns, they measured the diameter of the vessels responsible for water transport, leaf characteristics related to resistance to water stress, and tree growth before, during, and after the dry season in 2023–2024, when the region was affected by the El Niño climate phenomenon. The results showed that tall trees have developed anatomical and functional adaptations that compensate for the physical demands associated with their height.
“Understanding the biology of the tallest trees has a direct impact on estimates of future carbon stocks in tropical forests. Just one percent of the tallest trees contain more than half of the above-ground carbon stored in these forests. Yet existing climate models have assumed that these very trees would be the most likely to die during droughts. However, our study shows that height does not have a negative effect on water transport, which suggests the need to reevaluate existing models of climate change impacts,” said wood anatomy expert Palasiah Jotan from the Faculty of Forestry and Wood Sciences at the Czech University of Life Sciences (ČZU), one of the study’s three lead co-authors.
Ecologist Martin Svátek from Mendel University emphasized that this is the first direct evidence of the hydraulic resilience of the tallest tropical trees: “Thanks to a combination of anatomical, ecophysiological, and ecological methods, we have succeeded for the first time ever in demonstrating that even the tallest trees of the Dipterocarpaceae family are no more hydraulically vulnerable during drought than smaller individuals. Similar research will now need to be extended to other species of tall trees in other parts of the world.”
To verify how giant trees respond to drought stress, automatic dendrometers were used in conjunction with microclimatic sensors capable of accurately recording tree growth under environmental influences: “The instruments used are based on Czech technology and were manufactured right here in the Czech Republic. We found that during the most recent El Niño event, giant trees did not experience the same decline in growth as smaller trees. On the contrary, they showed a smaller decline in growth and a faster return to the values typical of the period before the drought,” added dendrologist Radim Matula from the Faculty of Forestry and Wood Sciences at the Czech University of Life Sciences (ČZU).
According to Roman Plichta, an expert in tree ecophysiology at Mendel University, the results also contribute to a better understanding of how trees function: “Trees are unique in that they can transport hundreds of liters of water per day from their roots to their leaves against gravity without consuming any energy themselves. It was previously assumed that this process becomes increasingly difficult with increasing height, especially during droughts. However, our results confirm that these giant trees are perfectly adapted to their height, and water transport does not yet represent a limiting factor for them.”
Link to the study: Height does not impair the hydraulic system of the tallest tropical Dipterocarp trees | Science