TreeWatch.net is a pioneering tree water and carbon monitoring network, in which high quality measurements of sap flow, stem diameter variation, stem water content and CO2 efflux will be collected in individual beech trees (Fagus sylvatica L.) along north-south trajectories in Europe. The unique dataset will be used to parameterize in real-time a mechanistic tree model to understand differences in growth, respiration and tree hydraulic responses to temperature and drought along trajectories through Europe from underlying water and carbon relationships.