The European Psi-leaf network for monitoring tree water status during extreme drought

Central Europe experienced extremely dry conditions in spring 2025, with weather forecasts predicting another extreme summer drought similar to that of 2018. To evaluate the impact of extreme climatic and edaphic drought on Central European tree species, coordinated midday leaf water potential measurement campaigns were carried out at 51 forest sites across Europe, covering a total of 12 common native tree species (four conifers, four diffuse- and four ring-porous broadleaves). Fortunately, the summer turned out to be rather moist, contrary to the early summer weather forecasts, while Northern and Southern Europe experienced extremely hot and dry conditions, setting several negative records. Nevertheless, the members of this initiative performed monthly measurements campaigns between June and October 2025 at their sites as baseline measurements, awaiting the next extreme summer drought to continue the measurement campaigns.

Here, we introduce the European Psi-leaf network, which is open to everyone as long as common protocols are followed. These include water potential measurements using classic pressure chambers, as well as additional information at tree and site levels. We also present species-specific results on leaf water status regulation during a non-drought year, revealing clear patterns across wood porosity types.