Effects of harvesting dates and frequencies on above and below-ground 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 grasslands in Belgium. Above and below-ground developments were analyzed. The vegetation changed evidently from the first spring after the establishment of the harvesting treatments onwards. One or two late summer and/or autumn harvests (August-October) led to lower productivity and higher species-richness. Generally, the reaction from the individual species was related to their capacity to germinate (Lychnis flos-cuculi L.) or initiate new tillers (Anthoxanthum odoratum L.), stolons (Agrostis canina L.) or rhizomes (Carex acuta L.). Not only did the total productivity decrease after one or two late summer and/or autumn harvests, but even the species increasing their cover/abundance after these treatments simultaneously developed less vigorous shoots. Soil analyses could not detect any changes in substrate fertility. However, analyses of nutrients in roots and rhizomes indicated lower concentrations of phosphorus and potassium in harvested conditions. Thus, the quick response of vegetation to the different treatments was related to its adapting species composition and to a depletion of phosphorus and potassium in roots and rhizomes. A depletion of nutrients in the soil was not detected.