PHYTOSOCIOLOGY AND PHYTOGEOGRAPHY OF THE CALCAREOUS GRASSLANDS ON DEVONIAN LIMESTONE IN SOUTHWEST BELGIUM

In Belgium, most calcareous grassland relics are associated with Devonian limestone substrates in the Viroin valley, which is part of the Calestienne region. Previously grazed by sheep, these grasslands are characterised by an extremely high species richness and many rare plant species. Despite their high biodiversity, a detailed phytosociological classifi- cation and an ecological description of the relics of these grasslands do not exist. In spring and summer of 2003, the calcareous grassland vegetation on Devonian limesto- ne hills in the Viroin valley was inventoried. A total of 401 vegetation releves were established in 1 m 2 plots. Based on classification and ordination techniques seven vegetation types were distinguished. The main differences in species composition were explained by a gradient from xerophilous towards mesophilous environmental characteristics. The particular phytosociolo- gical and phytogeographical position of the calcareous grasslands in the Viroin valley is fur- ther discussed in a European context. Mesophilous calcareous grasslands in the Calestienne belong to the Mesobromion and show an intermediate position between the central European and the Atlantic calcareous grassland communities. The xerophilous calcareous grassland com- munities on the other hand show strong affinities with the calcareous vegetation of central Europe and southern Europe.