The key objective of this project is to quantify the impact of tree water use of distinct deep soil water for tree health and forest stability for key forest species in Europe. To achieve this, we will characterize the spatiotemporal behavior of the different water pools in the unsaturated zone in dependence to precipitation input and groundwater table depth, the spatiotemporal connectivity between trees and these pools and phenological and physiological drought responses of trees along topographic gradients in the field.
Our central hypothesis is that particularly connectivity to the capillary zone is a critical component of drought tolerance. However, its impact for tree health will vary among species (water use strategies, degree of isohydricity) and across sites (climatic conditions and geomorphological gradients).