Nutrient limitations in an extant and drained poor fen: implications for restoration

In a species-rich poor fen (Caricetum nigrae) and a species-poor drained fen, the difference in nutrient limitation of the vegetation was assessed in a full-factorial fertilization experiment with N, P and K. The results were compared to the nutrient ratios of plant material and to chemical analysis of the topsoil. A rewetting experiment with intact sods was carried out in the glasshouse and the results are discussed in view of restoration prospects of drained and degraded peatlands. In the undrained poor fen the above-ground biomass yield was N-limited while the vegetation of the drained fen was K-limited. Experimental rewetting of intact turf samples, taken in the drained site, did not change the biomass yield or the type of nutrient limitation. It was concluded that mire systems which have been subjected to prolonged drainage are inclined to pronounced K-deficiency, probably due to washing out of potassium and harvesting the standing crop. This may hamper restoration projects in degraded peat areas where nature conservation tries to restore species-rich vegetation types with a high nature value.