Pedogenesis in coastal wet dune slacks after sod-cutting in relation to revegetation

The development of vegetation and soil was investigated in wet coastal dune slacks in North Holland, The Netherlands (52 degrees 36'N, 4 degrees 37'E). Sod cutting in the past has created a time series from 1 to 30 years, with an even older undisturbed site as reference. After sod-cutting Schoenus nigricans, a typical pioneer species of wet dune slacks, established and contributed together with Calamagrostis epigejos to more than 85% of the aboveground biomass. At the control site the biomass was 9.5 t dry matter ha(-1). The humus layer increased to a thickness of 11 cm. The concentration of nitrogen, phosphorus and potassium increased in the humus layer without strong effects on the sandy subsoil, in contrast to the strong decalcification in the subsoil. The velocity of the latter process was a factor of hundred higher than reported from dry dunes in the same area. Changes in nutrient amount and availability affected the element concentration in the two dominant plant species. The nitrogen concentration in shoots of S. nigricans was nearly constant over time, whereas that in shoots of C. epigejos declined by 80%. Due to the increasing biomass the size of the N- and P-pool of the biomass increased with the age of the plots. Processes of vegetation development and pedogenesis are not (yet) affected by decalcification as established by the nut mass of S. nigricans. It is concluded that decalcification is not the key factor for the disappearance of rare species. Due to the dominance and the height structure of the two dominant plant species competition for radiation and lack of bare soil for germination are discussed as main reason for losses in biodiversity. It is advised that mowing may be an effective management tool for hampering the soil formation; but sod-cutting may be necessary once in every decade.