Résumé
This chapter aims to discuss some aspects of the functioning of perennial woody species by briefly reviewing the main features of Mediterranean-type ecosystem resources and illustrating how individual and ecosystem cope with variability in water resource and control water loss. Its also include: presenting the assimilation characteristics in relation to constraints, and evaluating the role of nutrients at plant and community levels. The dominance of sclerophyllous—leathery, rigid, and heavily cutinized leaves—evergreen plants in the five Mediterranean-type ecosystems of the world has been interpreted since a long time as a convergent adaptation in responses to the unique environmental conditions associated with Mediterranean climate. The main climatic factor controlling the functioning of these ecosystems is water availability, which varies greatly in time and space, imposing strong constraints over the plant. From an ecological point of view, the variability or unpredictability of precipitation imposes strong constraints on plants that could be more important for the survival of individuals that the mean values.