Vegetation change in a lichen-rich inland drift sand area in the Netherlands
Ketner-Oostra, Rita; Sýkora, Karlè V
In this paper we compare the cryptogam vegetation in the Spergulo-Corynephoretum and Genisto-Callunetum in an inland drift-sand area in three periods (1968, 1993 and 2004). In the early period the lichen diversity in these plant communities appeared to be very high. The aspect was formed by Corynephorus canescens and Polytrichum piliferum. The highest numbers of lichen species are found in the S.-C. cladonietosum, irrespective of the period. In all years, variants of this subassociation are found, with many lichen species. In time pH decreases and organic matter, % total N and % total P increase by humus production. Cover sands having relatively high content of cations form a suitable substrate for lichens. Since the 1970s the neophytic moss Campylopus introflexus, a species adapted to acidic, nutrient-poor sand, has invaded the sand dunes. These changes have been attributed to the high aerial deposition of N in this central part of the Netherlands. In the more recent periods the actual lichen diversity did not really diminish, but the cover of lichen-rich plant communities was clearly reduced when encroaching mosses outgrew the lichens in all succession stages. However, when C. introflexus is less vital because of ageing, desiccation or burial under wind-blown sand, common humicole, aero-hygrophytic and even pioneer lichen species may locally establish on or between the moss cushions. The former succession series starting with P. piliferum and ending with lichen-rich Calluna heath (1968) has been partly replaced by one including C. introflexus (1993 and 2004). Process management is necessary to keep the sand blowing and hereby reduce the colonization by C. introflexus. Habitat restoration by small-scale management consisting of cutting down self-sown trees and removing the top soil has positively influenced lichen diversity and needs to be continued.