Primary succession of bryophyte and lichen communities in non-forested Atlantic coastal dunes:: the example of the Pointe d'Arcay (France)

The distribution of bryophytes and lichens growing on non-forested coastal dunes along the Atlantic seaboard of France was studied from vegetation surveys that were analysed by multivariate analyses. The dune system of the Pointe d'Arcay is unusual in its geomorphology and illustrates a chronosequence. It is a good example of succession in bryophyte and lichen communities on a sandy alkaline soil whose calcium content is gradually being leached out. Seven groups of bryophytes and lichens corresponding to four stages of a primary succession and one stage of a secondary succession are described. Two bryophyte and lichen habitats were distinguished: the juvenile fixed grey dune and the mature fixed grey dune. The highest diversity of bryophyte and lichen species was found in the semi-fixed to fixed parts of the dunes (about 50 years of stabilisation). The dominant mechanisms observed in this primary succession appeared to be mainly related to abiotic environmental conditions, which vary with time, and to certain biological traits of the species.