... rela-tionships in Acer opalus and Fraxinus excelsior trees growing in the valley of the Drac river. The experiments were carried out in the last days of July 20 00. Data are the means of ten determina-tions ... wet (A, D) orin dry conditions (B, C, E, F).For dry conditions, two different sites were selected, one in the valley of the Drac river, the other in a mountain stand in the Alps. The experiments ... remain close to itsmaximun value during the morning and the beginning of the afternoon, allowing a high transpiration rate (4.8 and3.9 mmol m 2 s–1for maple and ash trees, respectively, in June,...