Effects of grass-encroachment on vegetation and soil in Dutch dry dune grasslands

The encroachment of tall grass species in open dune vegetation, as observed in the Dutch dry dune area, is considered unfavourable for nature conservation. The effects of grass-encroachment on the vegetation and the availability of light and its relation to nutrients were investigated through a comparative study of grass-dominated and open dune grassland plots at ten locations along the Dutch coast. Grass-dominated plots have a low species diversity and number of species, especially of mosses and lichens. This is associated with a high biomass and a low availability of Light at soil surface. In addition, nutrient availability seems to be important. Root biomass and the amounts of both ectorganic and endorganic matter are significantly higher in grass-dominated plots, which may account for the higher nutrient uptake in the vegetation. It is likely that a grass-dominated system can maintain and consolidate itself because of the better competition for light and nutrients. The relevance of these results for restoration management is briefly discussed.