Why Trees Respond Differently to Repeated Drought
Not all trees get thirsty in the same way. And above all, they don't all recover in the same way after a hot, dry spell.
A study published on October 9, 2026, in the European Journal of Forest Research sheds valuable light on this issue. By analyzing 29 species across 130 European forest sites, researchers show that wood anatomy influences the duration and frequency of water deficits experienced by trees.
Observing a tree that is dehydrating… down to the millimeter
The study relies on dendrometers, instruments capable of measuring very small variations in trunk diameter. When a tree loses water and its tissues dehydrate, its trunk contracts slightly. When it rehydrates, it regains volume.
Using data collected between 2003 and 2018, the authors studied the duration of trunk water deficit periods, their intensity and their possible repetition during the same summer.
Heat, dryness, and incomplete recovery: the trio that prolongs stress
The main finding seems intuitive, but it has now been quantified on a large scale: the more severe the dehydration and the more incomplete the recovery, the longer the period of deficit. Higher temperatures and drier conditions also prolong these episodes.
But the reaction varies depending on the type of wood. The researchers distinguished between conifers, ring-wood species, and diffuse wood species. Conifers and ring-wood species reacted more strongly to the intensity of dehydration. Diffuse wood species, on the other hand, were more sensitive to repeated episodes of dehydration during the same season.
For these latter species, the recurrence of a new episode of water deficit increased the expected duration of the following episode by approximately 12%. Therefore, it is not only the drought itself that matters: its repetition and the tree's hydraulic architecture also play a role.
A French forest that is already showing signs of tension
These results strongly echo the findings of the 2026 National Forest Inventory. The IGN (National Institute of Geographic and Forest Information) observes a decline in the health of French forests, an increase in mortality, and a slowdown in carbon sequestration. It also highlights the role of soil: more than half of French forests grow on soils with very low available water capacity.
In other words, discussing forest adaptation requires considering the tree species, wood type, soil, water availability, microclimate, and recent drought history together. There is no single "miracle" species capable of solving the problem on its own.
View trees as organisms in balance
I particularly like what this research forces us to see: a tree does not go through a dry summer like a stationary object. It constantly adjusts its water balance, closes its stomata, modifies its growth, mobilizes its reserves and tries to rehydrate itself when conditions allow.
To understand what this means on a forest scale, you can also read the article on forest regeneration and the one on trees as carbon sinks.
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