Essential factors in wetland restoration are water level and groundwater quality. To support and preserve the vegetation of a nutrient-poor fen (Caricion nigrae) in the Lake Hohn area, Northern Germany, the water level was increased so that floods occur in winter. Fertilization of surrounding farmland was stopped in 1991.
In seven years the vegetation developed from Lolio- Potentillion and Cynosurion to Magnocaricion, Caricion nigrae (a frame community) and Calthion. There is also a shift from former Caricion nigrae to Magnocaricion and Phragmition communities. The species composition of the newly established and the older Caricetum nigrae is different. Only the older stands include indicators of mesotrophic soils such as Sphagnum spp., Pedicularis palustris and Succisa pratensis. According to an analysis of biomass, soil and groundwater composition the mire can be characterized as a poor fen. The low-productive vegetation is phosphorus-limited due to the influence of rain water. However, inundation of P-rich lake water may turn the poor fen into a fluviogenous fen with tallgrowing Magnocaricion vegetation.
Nutrients have traditionally been removed by cutting, crop removal and grazing. High water levels prevent the use of machines and result partly in an undesired abandonment. Moderate rising of the water level and a consequent cutti