Tree-specific point and band dendrometer measurements with a temporal resolution of 15-60 minutes were compiled from 85 monitoring plots across Europe. Plots within a Euclidean distance of 9 km, an elevational difference of less than 300 m, and similar soil water conditions were clustered, resulting in a total of 53 sites. For each site we also extracted time series of daily mean atmospheric temperature (in ��C) and vapor pressure deficit (in kPa), obtained from the nearest climate station (search radius = 80 km) using the Global Surface Summary of the Day (GSOD) Weather Data Client. Site-specific soil moisture data were obtained from the ERA-5 land surface model simulations (Layer 3: 28 ��� 100 cm depth). Relative extractable water was calculated to account for inter-site differences in soil properties and absolute soil moisture levels and to facilitate inter-site comparisons. Accompanied with the study, we provide the following supplementary data: * Data ��� Daily aggregation.xlsx = Daily aggregated values of the dendrometer derived parameters for each tree included in the dendrometer network and associated climatic information. * Data ��� Metadata sites.xlsx = Overview of all sites and trees included within the dendrometer network. * Data ��� Yearly aggregation.xlsx = Yearly aggregated values of the dendrometer derived parameters for each tree included in the dendrometer network and the associated climatic information. * Figure 2 ��� Boxplot data.xlsx = Basic data for generating Figure 2 of the manuscript. * Figure 3 ��� PFT response raster.zip = Raster data originating from the linear mixed-effect models explaining the tree water deficit responses to vapour pressure deficit and relative extractable water for the different plant functional types, as presented in Figure 3 of the manuscript. * Figure 4 ��� Species response raster.zip = Raster data originating from the linear mixed-effect models explaining the species-specific tree water deficit responses to vapour pressure deficit and relative extractable water, as presented in Figure 4 of the manuscript.

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.