Forests and Water: A Vital Balance in the Face of Climate Change

07 / 10 / 2025

On July 14–15, Basoa Fundazioa and USSE co-organized the course “Trees and Water” at the Miramar Palace in Donostia, as part of the UIK Summer Courses of the University of the Basque Country (EHU). These two morning sessions offered a deep dive into the relationship between forests and water, summarized below.

Trees are much more than part of the landscape: they are true factories of life, powered by water. They absorb moisture from the soil, move it up to their leaves, and then release part of it as vapor. Interestingly, this process helps form clouds—and with them, rain. It’s a fascinating cycle where forests not only consume water but also help generate it.

Yet this delicate balance is now at risk. Climate change is bringing longer, harsher droughts. When water becomes scarce, trees weaken: they lose leaves, slow their growth, and, in severe cases, die. What happens to one tree may seem trivial, but when it occurs at scale, entire forests lose strength, and with them, the vital services they provide—from climate regulation to replenishing rivers and reservoirs.

Although southern Iberia is the hardest hit, early warning signs are already appearing in Álava and Navarre. Research worldwide shows that even tropical forests—often imagined as overflowing with water—are suffering from drought stress. In contrast, Mediterranean species, accustomed to scarcity, withstand it better—up to a point. The water stress brought by global warming is already causing widespread tree mortality.

Science has pinpointed one key process: cavitation. When water is lacking, air bubbles form inside the tree’s water vessels, blocking the flow like clots in a bloodstream. If this persists, the tree eventually dries out. Understanding this mechanism is essential to predict how forests will respond to future extreme conditions.

Faced with this reality, active forest management is crucial. Sustainable forest management strategies can help trees cope. One of them, ecohydrology, studies how water is distributed among soil, vegetation, and the atmosphere. Through measurements and modeling, managers can simulate different scenarios and decide which practices—such as thinning certain areas or diversifying species—work best for each site.

The case of pine species illustrates these varied responses. In Álava, Scots pine suffers greatly from water shortage, showing more defoliation, slower growth, and higher mortality. Aleppo pine, typical of Mediterranean areas, is also affected by drought, pests, and fire. Radiata pine, however, faces a different threat: in the humid Cantabrian zone, higher temperatures are encouraging the spread of diseases. Each species, therefore, demands its own adaptive strategy.

A key strength of this course was the participation of forest owners and managers, who play a decisive role in turning scientific knowledge into practice and raising public awareness of the importance of forests. While society may not yet fully grasp their crucial role, communication and outreach must intensify.

Ultimately, protecting forests is not only an environmental issue—it’s an investment in our future. Their roots hold much more than trees; they hold life itself.

Videos from the course “Trees and Water” are available on our YouTube channel.

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