Data from: Normalized tree water deficit: An automated dendrometer signal to quantify drought stress in trees

This dataset accompanies the manuscript "A normalized dendrometer-based index to detect drought stress across temperate tree species". The study addresses a central challenge in tree ecophysiology: identifying the timing and intensity of drought stress in mature trees using continuous, non-invasive measurements. Trees regularly experience periods of low soil water availability and high atmospheric demand, which can impair physiological processes such as stomatal conductance, leaf turgor, and growth. While automated dendrometers offer high-resolution insights into stem dynamics, a robust framework for interpreting these signals as direct indicators of drought stress has been lacking. We introduce a novel, biologically grounded index—normalized tree water deficit (TWDnorm)—derived from dendrometer data, in combination with normalized maximum daily shrinkage (MDSnorm). These indices provide a standardized way to detect drought-induced stress responses in trees. To validate the approach, we integrate concurrent measurements of leaf water potential (Ψleaf), stomatal conductance (gₛ), and hydraulic vulnerability across 118 mature trees representing nine widespread European tree species. All data were collected at the Swiss Canopy Crane II research site under diverse environmental conditions. The dataset includes physiological and stem diameter dynamics from both broadleaved species (Fagus sylvatica L., Acer pseudoplatanus L., Carpinus betulus L., Fraxinus excelsior L., and Quercus petraea/robur L.) and conifers (Abies alba Mill., Picea abies Karst., and Pinus sylvestris L.). Our findings show that TWDnorm reliably signals the onset of stomatal closure and leaf turgor loss, with species-specific thresholds that can inform drought vulnerability assessments. The combination of TWDnorm and MDSnorm thus represents a novel, automated index for biological drought stress, complementing traditional meteorological and satellite-based drought indicators.