The European beech (Fagus sylvatica) is one of the most common and ecologically important tree species in Swiss and European forests. But its sensitivity to drought threatens the stability of Switzerland’s forests in the face of an increasingly hotter and drier climate. To investigate how beech can persist in these changing conditions, 190 four-year-old beech saplings were planted as part of a biodiversity experiment on Irchel Campus.

Beech trees can adapt through genetic variation, phenotypic plasticity, and interactions with other organisms. How much does each factor contribute? We need to better understand how beech populations grow and perform under different conditions to take effective decisions for forest management.

Beech forests are part of Switzerland’s cultural heritage

As the most common broad-leaved tree in Switzerland, beech has shaped many lowland forests for centuries. It provides habitat for specialized organisms and delivers essential ecosystem services such as carbon storage, timber production, and climate regulation. In 2021, two ancient beech forests in the Jura and Ticino were added to the UNESCO World Heritage list.

Therefore, if beech were to decline, the consequences for Swiss forests would be severe. In our research, we try to find key insights into the future of beech forests under climate change. One possible key to resilience lies in the genetic diversity within beech populations, as some genetic variants may be better suited to future climate conditions. At the same time, non-genetic adaptive responses may allow individual trees to adjust to changing environmental conditions over their lifetime.

Two new beech common garden experiments established

To find out how and if beech has the genetic diversity to be resilient to climate change, we established two new beech common garden experiments in November 2025. There, beech individuals from very different geographic and genetic backgrounds are exposed to the exact same environment and their performance is monitored over the years.

Experiment 1: A small genetic diversity experiment at Irchel Campus, University of Zurich

On 26 November 2025, we planted 190 four-year-old beech saplings in the experimental garden on Irchel Campus. Despite a muddy and snowy start, we were happy to finally get the young trees into the ground.  And these trees have a special origin story. The seeds were collected across Europe in 2020 from well-protected forests dominated by natural beech populations.

Now, they are growing under two contrasting genetic diversity levels. Low genetic diversity means a group of saplings originating from the same region, high genetic diversity means mixing saplings from all across Europe. This new experiment will thus test how genetic diversity within beech influences growth, drought stress tolerance, and ecosystem functioning—key information for managing future forests in a changing climate. We are excited to continue to watch the young trees grow.

Experiment 2: A continental-scale provenance trial in Effretikon, Switzerland

Just two weeks earlier, on 12 November 2025, a second major beech experiment was established in Effretikon, located between Winterthur and Zurich. Here, 450 young beech trees originating from across Europe were planted in the context of the larger Europe-wide MyGardenOfTrees research initiative of Katalin Csilléry at WSL, which investigates how European beech populations differ in their climate adaptation.

This experiment is one of several “macro-gardens” planted across Europe following a standardized protocol. For our macrogarden in Hackenberg, the local context highlights why such experiments are urgently needed: The large open area used as the planting site arose after severe drought and bark beetle outbreaks—an example of the pressures increasingly affecting Central European forests. And beech is increasingly struggling with climate-change driven heat and water stress.

By providing land, forest care, and long-term monitoring, the municipal forestry service contributes directly to our research aimed at ensuring that future generations can continue to enjoy a healthy and resilient peri-urban forest. The goal of the Effretikon trial is to observe growth, development, and adaptive potential of the more than 10 beech populations from across Europe under the local climatic conditions.

Sofia van Moorsel, Spatial Genetics

Buchen im Klimastress: Auf den Spuren der Buchen von morgen? Magazin dergartenbau, September 2025 Beech under global change: Untangling the genetic, physiological, and ecological foundations of drought tolerance SNSF Project, 01.01.2026 – 31.12.2029