After a very wet spring, a severe drought has occured from July to August with very low rainfall (20 mm for the two months) and high temperatures (days above 35°C). These weather conditions added to the harsh soil conditions of the Orleans forest led to significant stress for the trees. To better understand the effects of drought on tree functionning, experiments were conducted during the summer as part of the thesis of Jordan Bello (PhD student, Irstea). Two methods were carried out: the first method is based on measuring the base water potential of trees and the second is based on the measurement of oxygen isotope ratio in soil and wood. These methods make it possible to estimate the stress suffered by trees and the depth of water uptake by each species. The sampling was designed in order to see whether stress and depth of water uptake during drought depend on stand composition (monospecific or mixed).