Soil organic matter accumulation and its implications for nitrogen mineralization and plant species composition during succession in coastal dune slacks.

Vegetation and soil development during succession in coastal dune slacks on Terschelling island, the Netherlands, was investigated, by comparing neighbouring ecosystems on similar substrates that had been developing for 1, 5, 35 and 76 years since the vegetation and organic soil layer had been removed. In this successional sequence, soil organic matter accumulated rapidly due to the production of litter and dead roots. N mineralization was extremely low, increasing from 0.2 g m-2 yr-1 after 5 years to 0.8 g m-2 yr-1 after 76 years. It was accompanied by a decline in the pH (KCl) in the upper 10 cm of the soil from 6.8 to 4.4. Most of the above-ground biomass accumulated in the shrub species Oxycoccus macrocarpos and Salix repens. The 5- year-old plots harboured many plant species (18 species per 0.25 m2), but plant species diversity was much lower in the older plots. It is concluded that most changes in species composition and the decline in diversity occurred because early successional plant species were gradually outshaded by the thick litter layer and the accumulated shrub biomass