EFFECTS OF HARVESTING DATES AND FREQUENCIES ON ABOVE AND BELOWGROUND DYNAMICS IN BELGIAN WET GRASSLANDS

A trial was established to assess the effects of harvesting dates and frequencies on the species, biomass and nutrient dynamics in wet grass lands in Belgium. Above and below-ground developments were analyzed. T he vegetation changed evidently from the first spring after the establ ishment of the harvesting treatments onwards. One or two late summer a nd/or autumn harvests (August-October) led to lower productivity and h igher species-richness. Generally, the reaction from the individual sp ecies was related to their capacity to germinate (Lychnis flos-cuculi L.) or initiate new tillers (Anthoxanthum odoratum L.), stolons (Agros tis canina L.) or rhizomes (Carex acuta L.). Not only did the total pr oductivity decrease after one or two late summer and/or autumn harvest s, but even the species increasing their cover/abundance after these t reatments simultaneously developed less vigorous shoots. Soil analyses could not detect any changes in substrate fertility. However, analyse s of nutrients in roots and rhizomes indicated lower concentrations of phosphorus and potassium in harvested conditions. Thus, the quick res ponse of vegetation to the different treatments was related to its ada pting species composition and to a depletion of phosphorus and potassi um in roots and rhizomes. A depletion of nutrients in the soil was not detected.