Réponses fonctionnelles des communautés de pelouses calcicoles aux facteurs agro-écologiques dans les Préalpes françaises

Abstract

The identification of functional groups in calcareous grasslands of southern Vercors (Rhône-Alpes, France) is investigated through relationships between biological traits of the species and agro-ecological factors. Community patterns are determined by (i) the level of edaphic stress (oligotrophy and xericity) and (ii) the regime and the intensity of agropastoral management (grazing and mechanical cutting). In such grasslands submitted to regular disturbance, life traits related to dispersal and regeneration processes have greater importance for the differentiation of species than morphological traits, and Grime's adaptative strategies are the best predictors of species ordination on agro-ecological gradients (e.g., stress and disturbance). A classification of species in functional groups based on the same life traits and similar responses to disturbances is proposed, and its role in defining adequate conservation management of calcareous grassland by low-intensity livestock farming is discussed. The functional role of grazing is emphasized by the relationship between species dominance or rarity and their levels of consumption and dispersion by sheeps. In calcareous grassland communities, dominant species are the most palatable and the most dispersed by sheeps, while rarer species depend on other dispersal modes, such as seed rain or mowing machinery.Key words: life traits, functional groups, agropastoral practices, conservation management, RLQ analysis.