Biotechnologie, Agronomie, Société et Environnement (Jan 2005)
Rémanence des utilisations anciennes et gestion conservatoire des pelouses calcicoles en France
Abstract
Persistence of former land-uses and conservation management of calcareous grasslands in France. In Europe, a lot of chalk grasslands are managed for the conservation of their great biodiversity. However, traditional agricultural practices are at the origin of their existence and maintained them. Although these practices are becoming well documented, very few studies are carried out on the links between traditional agricultural practices and long-term vegetation dynamics. Most of these practices have been abandoned during the last centuries. The aims of our study were to identify the traditional agricultural practices and their impacts on the composition, structure and dynamics of chalk grassland vegetation in interaction with the influence of new management systems created for their biological conservation. Three study sites were chosen in a gradient from North-West France to South-East France. In the chalk grasslands of Upper-Normandy (NW), our results showed that the species which disappeared or are about to disappear from the above-ground vegetation are arable weed species of the 19th century cultivated plots and not typical species of nowadays chalk grasslands. In the centre of France, our results showed that,whatever the present disturbance regimes, old calcareous grasslands always have a higher species richness than grasslands close to former cultivated plots. In South-Eastern France, our results showed that formerly cultivated plots have a very different floristic composition than grazed grasslands. Also, their species-richness is always significantly lower than that of grazed grasslands even after 35 years of abandonment and with the same present disturbance regime. Dry grasslands are not resilient to punctual disturbances taking place within centennial disturbance regimes. Managers must take into account these parameters to set their management priorities. Concurrently to ecological diagnosis and biodiversity inventories, they must carry out historical ecological studies to understand more clearly which variables are responsible for the structure and dynamics of these ecosystems.
