Nutrient status,disturbance and competition: an experimental test of relationships in a wet meadow

Abstract. In many species-rich hay meadows in Central Europe, the traditional extensive (low input, low output) management is no longer economical and meadows are either fertilized or abandoned. Both these practices lead to changes in species composition and usually to a loss in species diversity. The response of a species-rich meadow plant community to fertilization, mowing and removal of dominant species was studied in a manipulative factorial experiment over four years. Both species richness and seedling recruitment were positively influenced by mowing and to a lesser extent by removal of the dominant species, Molinia caerulea, and were negatively influenced by fertilization. Fertilization caused an immediate increase in community biomass. Response to removal of the dominant species was delayed by one season, continued over the whole period, and by the fourth year the biomass reached a similar value as in the plots with Molinia present. Changes in species composition were evaluated by RDA for repeated measurements. The best and only significant predictor of species response to fertilization was plant height. This shows that with increased nutrient availability, nutrient limitation weakens and competition for light becomes the decisive factor. Competition for light appears to be more asymmetric than competition for nutrients, and consequently, it is more likely to drive inferior species to extinction. This is, together with seedling recruitment limitations, the most important cause of a decrease in species richness under high nutrient levels.