Canopy thermoregulation of Quercus ilex under long-term soil moisture reduction across a Mediterranean climate gradient

Mediterranean forests are increasingly exposed to hotter and drier summers, yet the mechanisms by which mature trees regulate canopy temperature under chronic soil moisture limitation remain poorly constrained. We investigate ecosystem-scale drivers of canopy thermoregulation and consequences for leaf thermal safety margins and function in Quercus ilex in southern France (Puéchabon) and northeastern Spain (Prades), where throughfall exclusion has reduced soil moisture by ~30% for over two decades. Combining continuous micrometeorological measurements with seasonal observations of canopy temperature, gas exchange, sap flow, and thermal tolerance, we ask whether long-term drought acclimation alters canopy-level physiological responses in ways that modify or maintain leaf thermal safety margins. We test the hypothesis that chronic soil moisture reduction leads to reduced transpiration, resulting in warmer canopies during the growing season, but that drought-acclimated trees exhibit altered stomatal sensitivity that mitigates leaf overheating during heat waves. We further assess whether recovery of transpiration following hot periods differs between control and drought-treated trees and whether responses vary between cooler and warmer sites. This work leverages long-term field experiments to improve mechanistic understanding of tree thermoregulation under future Mediterranean climate extremes.