Decline of lichen-diversity in calcium-poor coastal dune vegetation since the 1970s, related to grass and moss encroachment

Since the 1970s the encroachment by tall graminoids, especially of Ammophila arenaria, has changed the aspect of the calcium-poor 'grey dunes' of the Wadden Sea island Terschelling (The Netherlands) formerly dominated by Corynephorus canescens. In addition, the neophytic moss Campylopus introflexus, a species adapted to acid open sand invaded these dunes. In this paper the cryptogam vegetation inside dry dune-grassland (the Corynephorion, the Tortulo- and Polygalo-Koelerion) and dune-heath (Empetrion) before (the 1960s) and after these changes (the 1990s) are compared. It was found that in the former period the lichen diversity in several plant communities was very high, amounting to a total of 45 species, among which 10 epigeic growing species that are usually epiphytes. In the latter period, Campylopus introflexus not only outgrew the rare lichens from the pioneer stage of the Violo-Corynephoretum, but also the more: common pioneer species of decalcified sand. However, when this moss has lower vitality through desiccation or being blown-over by sand, common humicolous lichens and some pioneer species may act as secondary pioneers on these withered moss carpets. In the 1990s some relatively open communities were still present in a transition stage of the Violo-Corynephoretum to the Phleo-Tortuletum and in the Phleo-Tortu- letum itself, forming a suitable environment for some lichen pioneer species of subneutral sand, including some of the epigeic growing epiphytes.