Mesotrophic basiphilous communities affected by changes in soil properties in two dune slack chronosequences

Two soil chronosequences were investigated to identify soil properties related to acidification during succession of dune slack vegetation. One chronosequence was associated with a primary succession series on a wet beach plain on the Dutch island of Schiermonnikoog, the other with a succession series after sod cutting in a secondary (blown out) slack on the island of Terschelling (the Koegelwieck). Both chronosequences include a succession sequence which starts from bare sand, proceeds to basiphilous, mesotrophic (low productivity) vegetation types (Junco baltici-Schoenetum nigricantis) with many rare species, and ends with productive shrubbery or forested, acidified organically enriched soils with little floristic value. The pH decreased with time in both chronosequences. In the beach plain this was correlated with an increase in organic matter and a decrease in salt content. In the blown out slack the pH decrease was correlated with an increase of organic matter and with an increase in exchangeable bases, except for Ca, on the exchange complex. The faster organic matter increase and pH decrease in the blown out slack chronosequence resulted in a relatively short persistence of mesotrophic vegetation type with endangered basiphilous species. The mesotrophic basiphilous vegetation persists for a longer time (c. 20-25 years) in the initially calcareous beach plain chronosequence with a high acid buffering capacity as compared to the Koegelwieck chronosequence with a low acid buffering capacity.