EFFECTS OF GRASS-ENCROACHMENT ON VEGETATION AND SOIL IN DUTCH DRY DUNE GRASSLANDS

The encroachment of tall grass species in open dune vegetation, as obs erved in the Dutch dry dune area, is considered unfavourable for natur e conservation. The effects of grass-encroachment on the vegetation an d the availability of light and its relation to nutrients were investi gated through a comparative study of grass-dominated and open dune gra ssland plots at ten locations along the Dutch coast. Grass-dominated p lots 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 availabil ity seems to be important. Root biomass and the amounts of both ectorg anic and endorganic matter are significantly higher in grass-dominated plots, which may account for the higher nutrient uptake in the vegeta tion. It is likely that a grass-dominated system can maintain and cons olidate itself because of the better competition for light and nutrien ts. The relevance of these results for restoration management is brief ly discussed.