Influence of agro-ecological factors on orchid assemblages in the calcareous grasslands of the southern French Prealps

The prealpine calcareous grasslands of the Vercors Natural Park (Rhones-Alpes, France) occurring in mountainous areas of south-eastern France have been poorly studied, although they provide suitable habitat for rare plant species especially orchids. In this study, we focused on the effects of habitat conditions and management regimes on their population assemblages (composition, structure, species-richness) in order to define adequate conservation management for the maintenance of species-rich orchid assemblages on both habitat and management gradients. The results showed that the grasslands of the Vercors Natural Park are characterized by the presence of species-rich orchid communities. This species-richness could be explained by the existence of a particular set of habitat conditions and management regimes where the following variables have the most significant effect (elevation, temperature, folding enclosure surface, type of herd and duration of grazing). Three response groups based on the measurement of orchid biological traits (e.g. biogeographical distribution, plant height, flowering periods, reproduction types) could be identified following the combination of habitat conditions and management regimes. In conclusion, two types of management systems could be proposed in accordance with the existence of two types of substrate (urgonian and marly limestone) to conserve the species-rich orchid communities of the Vercors Natural Park.