Land use history and botanical changes in the calcareous hillsides of Upper-Normandy (north-western France): new implications for their conservation management
Historique de l'utilisation des terres et des changements botaniques sur les collines calcicoles de Haute-Normandie (nord-ouest de la France) : nouvelles implications pour leur gestion conservatoire
Résumé
Historical studies were made of the changing land use (260-1995) of 14 calcareous hillsides in Upper-Normandy to investigate botanical changes over the last 200 years. Before the French Revolution in 1789, most of these hillsides were used as vineyards mixed with common sheep walks. After the French Revolution, they were distributed among inhabitants for cultivation (cereals) but they were abandoned in the nineteenth century and grazed again. Our results show that this history is correlated with important changes in the floristic composition of the calcareous hillsides between 1816 and 1995. The species richness of arable weeds and fallow-land species of former cultivated fields or vineyards decrease faster than that of chalk grassland species. The consequences of these long-term dynamics are discussed with regards to the ecological requirements and the rarity status of the species that have disappeared since 1935. We conclude with the need to take account of land use change processes, e.g. the alternation of arable fields and grasslands, to maintain the present species-richness of calcareous hillsides