Many rare plant species occur in Dutch wet dune slacks, particularly in the Junco baltici-Schoenetum nigricantis. For nature management it is important to understand the processes controlling the presence of these basiphilous early successional communities, which is why we investigated vegetation and soil development during succession in coastal dune slacks. We compared 12 chronosequential stages of 0, 2, 4, 9, 10, 13, 25, 30, 43, 60, 70 and 85 yr in five different dune slack systems. In four of these locations turf had earlier been removed in order to restore the basiphilous pioneer stage.
The main variation in the vegetation is related to the acidification/soil enrichment gradient and the salinity/maritime gradient. During succession, organic matter accumulates and acidification takes place. Maritime influence can buffer the soil and postpone the succession of basiphilous pioneer communities for many years. A significant correlation with age was found for 18 variables. Multiple regressions predicted changes in the vegetation (dependent variables: biomass, cover of Salix repens, Calamagrostis epigejos and Schoenus nigricans) as a function of acidification, organic matter accumulation, increase in available P and presence of Na in the soil.
We conclude that natural ageing of the vegetation and the associated process of accumulation of biomass drive succession in this hydrosere. The underlying soil processes are acidification and organic matter accumulation. During succession dominance shifts from S. nigricans to S. repens or C. epigejos. Maintenance of the pioneer character of the habitat is only possible by local intervention or by natural or man-induced dune forming. The effect of sod-stripping depends on the environmental conditions and, in case of acidification, success is limited. Succession can be postponed by mowing.
Abbreviations: ROL = Radial oxygen loss.
Nomenclature: van der Meijden (1990) for vascular plants; Touw & Rubers (1989) for mosses; Gradstein & van Melick (1996) for liverworts; Schaminée et al. (1995, 1996, 1998) for syntaxa. Agrostis stolonifera was probably identified as A. canina in some cases. The liverworts Moerckia hibernica and Pellia endiviifolia may have been confused but probably co-occurred in most plots.
