One-yr-old wild cherry (Prunus avium L) plants were grown as follows: 1) in small cylindrical shelters (diameter 50 cm, treatment S); 2) in large shelters (diameter 100 cm, treatment L); or 3) without shelter (control, treatment C) during 1 growing season. Treatment C was characterized by higher values of photosynthetic photon flux density (I(p)) and of leaf-to-air water vapour pressure difference (DELTAW) than treatments L and S. The plants were taller in treatments L and S than in treatment C but biomass production was higher in the latter treatment. The plants of treatment C were also characterized by higher values of CO2 assimilation rate (A) and of leaf mass per unit area (LMA, ratio of leaf mass to leaf area). Relative carbon isotope composition (delta(p)) of the leaves was higher in treatment C than in treatments L and S, which expresses higher time-integrated values of plant intrinsinc water-use efficiency (Alg ratio) in the former treatment. There was a positive correlation between delta(p) and LMA. Thus, LMA, a readily measurable parameter, is a relevant parameter for understanding and modelling water-use efficiency of canopies.