Different method to assess water use efficiency in a mediterranean beech forest

Increasing concentrations of atmospheric CO 2 is affecting the temperature and precipitation pattern driving significant modifications in natural and managed forests (Kirilenko & Sedjo, 2007). In the 21st century, the Mediterranean area might be an especially vulnerable region to global change (Giorgi & Lionello, 2008). Owing to its sensitivity towards low water availability (Ellenberg, 1996) and longer drought periods (Fotelli et al., 2002), physiological performance, growth and competitive ability of beech may be adversely affected by such changing environmental conditions (Peuke et al., 2002), also with a probable strong economical impacts being this species one of the most important in Europe (Geßler et al. 2007). Various definitions of WUE are applied in different scientific disciplines, but the common characteristic is that WUE is always a ratio of carbon gain to water loss (Saurer et al., 2004; Kuglitsch et al., 2008). WUE is dependent by the temporal and spatial scales and can be calculated using different methods (Ponton et al., 2006; Kuglitsch et al., 2008; Peñuelas et al., 2008). Hence, comparative studies of WUE are important for helping to understand how future climate change will affect the carbon and energy budgets of ecosystems (Ponton et al., 2006). In this context we assessed WUE efficiency in a Mediterranean beech forest using five methods. We calculated WUE using cuvette (LiCor 6400) in 8 days of different growing season, ? 13 C in tree ring cellulose, eddy covariance technique, 3D-CMCC-FEM and Modis data. The objectives were to compare the different methods and evaluate the effect of environmental variables on intra and interannual WUE.