Geosynphytosociological Typology of French Atlantic Coastal Rocky-Cliff Vegetation

Coastal cliff vegetation is spatially organized into parallel belts according to ecological gradients caused by salt spray, wind exposure, relief energy, substrate nature and depth. Along the French Atlantic coasts, a recent research programme set up in 2011 is dedicated to a geosynphytosociological study of coastal vegetation. The present work focuses on permanent vegetation of the French Atlantic coastal rocky cliffs, corresponding to permaseries. Permaseries occuring within homogeneous geomorphological units are listed within geosynreleves. The analysis of a set of geosynreleves from northern France up to the Pyrenees-Atlantic allows us to characterise phytocoenotical diversity and to propose a preliminary typology of coastal cliff vegetation. The geopermaseries assemblies follow Dupias’s and Rey’s phytoecological regions. These biogeographical units are more precisely characterized by substrate and climate. This analysis completes Gehu’s works about sigma-association description of French Atlantic cliffs. Eleven geopermaseries of rocky coast are defined: Sandstone or marly-cliff geopermaseries of Boulonnais; Marly and chalky cliff geopermaseries of Boulonnais; Chalky-cliff geopermaseries of Pays de Caux; Crystalline-cliff geopermaseries of the Gulf Normand-Breton; Crystalline-cliff geopermaseries of the western Massif Armoricain, under a hyper Atlantic climate; Crystalline-cliff geopermaseries of the southern Massif Armoricain, under a thermo-Atlantic climate; Crystalline-cliff geopermaseries of islands of the southern Massif Armoricain, under a thermo-Atlantic climate; Cliff-top fossil dune geopermaseries on sandy decalcified substrates; Calcareous cliff geopermaseries of the right-bank of the Gironde estuary, under a thermo-Atlantic climate; Chalky and sandstone cliff geopermaseries of the south-Aquitan Basin; and marly-chalky or sandstone cliff geopermaseries of the Corniche Basque.