Tree water status behavior of two common European urban species using dendrometric measurements and remote sensing imagery

With growing urban populations and rising heatwaves, urban trees are increasingly valued for their cooling benefits through transpiration and shading. However, water stress can limit transpiration, and the effects of urban environment and species-specific traits on tree water status remain understudied. This work investigates how meteorology, soil imperviousness and species influence tree water status behavior, and how vegetation indices derived from remote sensing relate to tree water status, at both seasonal and individual tree scales. Eleven mature Acer platanoides and Tilia x euchlora trees (two common European urban species) growing under varying soil imperviousness levels in a medium-sized French city were monitored. For summer 2023 and spring 2024, two dendrometric indicators of water status - maximum daily shrinkage (MDS) and tree water deficit (TWD) - were calculated, and vegetation index NDVI was extracted from SuperDove imagery. Results show that TWD, more than MDS, effectively assessed tree water status and was closely linked to vapor pressure deficit and relative humidity. Higher soil imperviousness increased water deficit in both seasons, particularly for trees in pits. Acer platanoides exhibited a more isohydric strategy than Tilia x euchlora. NDVI was strongly correlated with TWD in summer 2023 (R² = -0.43), and with MDS in spring 2024 (R² = 0.40). These findings underline the value of dendrometric measurements in urban environments for understanding tree water status, and highlight the potential of very high spatio-temporal resolution satellite data to assess individual tree water status across cities, supporting improved management to maximize the cooling benefits of urban trees.