The study of the influence of biodiversity on ecosystem processes is an expanding research as a result of the growing concern that loss of biodiversity may impair ecosystem functioning. An important generalization assumes a positive relationship among the community diversity and its stability in response to environmental disturbances, thus a key subject under the global change scenario. Recently, the functional approach to diversity (i. e. the functional expression of diversity) has emerged providing a closer explanation to the actual mechanisms of biodiversity-ecosystem functioning relationships than the traditional expression of diversity. An important number of studies have thrown some light on trait meanings and assessments; and several works have addressed the development of indices and mathematical frameworks to estimate functional diversity. However, these methods have often neglected the intraspecific trait variability (phenotypic differences within a species), commonly comparing mean trait values per species. The aim of this proposal is to understand the extent and implications of the inter and intraspecific trait variability on forest functioning, in particular on the recruitment process and the productivity across a climatic gradient in European forests. The rationale for including within-species variability is that European forests are relatively species-poor, so the phenotypic variation in functional traits within species is likely to be more relevant for a community and ecosystem processes that at species level. In this context, to disentangle the relationships between functional diversity and forest functions, we will characterise the inter- and intraspecific variability of functional traits in tree species, analysing the extent of each component in different forests across Europe (Germany, Romania, Finland, Italy, Poland and Spain) and the scale in which they are more relevant (individual, species, plot, region).