Urban tree water status response to environmental and physiological factors using dendrometer measurements and high spatial resolution imagery: the case of Tilia euchlora and Acer platanoides in Dijon city, France

In the context of increasing frequency of heatwaves, growing urban populations, and the intensification of the urban heat island effect, green infrastructure has become a key focus of interest. Among these, urban trees deliver significant environmental services, particularly cooling, through the processes of transpiration and shading. However, their cooling capacity depends on their water status, as water stress limits transpiration. The impact of urban conditions, such as soil imperviousness, and the influence of tree species on water status remain understudied. This study aims to assess the water status of urban trees and identify the environmental and physiological factors that influence it. The work was carried out in the city of Dijon, eastern France, and focused on 2 tree species commonly found in urban environments in European cities: Acer platanoides and Tilia euchlora. First, 11 mature trees with different urban morphological conditions were equipped with micro-dendrometers (PépiPIAF system) to record the daily stem diameter variations during summer 2023 and spring 2024. From these measurements, dendrometric indicators such as the maximum daily shrinkage (MDS) and the tree water deficit (TWD) were calculated to provide insight into tree water status. Analyses show that dendrometric indicators are influenced by meteorological variables, soil imperviousness and tree species, especially in summer. Then, for each instrumented tree, the normalized vegetation index (NDVI) was calculated from several high spatial resolution SuperDove satellite images during summer 2023 and spring 2024.  While the correlation between NDVI and dendrometric indicators is moderate to weak, it remains significant. Additionally, soil imperviousness significantly affects NDVI values. The next step is to establish a model that combines satellite data and dendrometric indicators to assess tree water status. This, in turn, could contribute to a better understanding and improvement of urban tree management.