Trees are reaching their limit in coping with future extreme droughts

Adapting to water scarcity is a strategy that woody plants, such as trees and shrubs, have developed throughout evolution, but they will increasingly be less able to do so. This is the conclusion of a new international study led by researchers from CREAF and ICIFOR (INIA-CSIC), which warns that this limitation puts many forests at risk if the climate continues to become drier and more extreme.

Over the past decades, many regions of the planet have experienced long and intense droughts. These conditions, combined with high temperatures, have caused mass tree mortality in different parts of the world. A study published in Nature Ecology and Evolution shows that plants can make certain adjustments in their hydraulic system to better withstand water scarcity, but these are no longer sufficient to cope with the water stress expected under climate change. The research used a global database containing information on the environmental adaptations of more than 230 woody plant species distributed across the planet.

“Resetting the hydraulic system is an evolutionary feature of plants to adapt to water scarcity, but when drought is extreme the system is failing them,” explains Maurizio Mencuccini, CREAF researcher and author of the study. 

Plants transport water from the roots to the leaves through a very delicate circulatory system known as the xylem. Under extreme drought, air bubbles —similar to embolisms— can form, blocking this transport and potentially leading to the plant’s death. Although plants try to become more resistant to these embolisms, the study shows that when water stress is very high, this mechanism is not effective enough.

Even though plants have developed mechanisms to adapt to drought, such as resetting their hydraulic system, the study also reveals that this mechanism is closely linked to other environmental factors associated with climate change, such as solar radiation, rising temperatures, increased atmospheric CO₂ concentration, or soil fertility.

The researchers found that the increase in CO₂ concentration in the air does not help improve the plants’ internal water transport system. Moreover, this excess CO₂ can cause plants to grow faster but without absorbing enough nutrients, which weakens them. As a result, the risk of water scarcity persists and may even increase.

Facing a future of climate change and the need for conservation actions, the researcher concludes: “We must not only think about plants having less water, but also consider all these factors to understand to what extent plants will be able to respond to an increasingly dry and extreme environment in order to plan ecosystem conservation actions.”

Study reference: Ramírez-Valiente, J.A., Poyatos, R., Blackman, C.J. et al. Limited plastic responses in safety traits support greater hydraulic risk under drier conditions. Nat Ecol Evol (2025). https://doi.org/10.1038/s41559-025-02830-4