Alternative management on fens: Response of vegetation to grazing and mowing

The impact of cattle grazing on the vegetation of calcareous fens was compared to the effects of traditional autumn mowing in southern Germany. Vegetation composition was studied in adjacent pairs of fen meadows and pastures with similar environmental conditions and biomass production. Vegetation data were analysed with respect to species richness, species composition and response of species traits to disturbance, including morphology, defence mechanisms, clonal growth form and generative reproduction. Species richness was significantly reduced by grazing, but the percentage of typical fen species or Red Data Book species was not affected by land use type. Detrended Corrspondence Analysis indicated that species composition could best be explained in terms of a land use gradient. Species traits showed a clear trend in their response to land use type. Grazing favoured grasses and small forbs. Only a few species with defence mechanisms against foraging were more frequent or abundant on pastures. Many other species with defence mechanisms, however, did not have an advantage on pastures. Flowering and seed dispersal traits did not respond significantly to grazing or mowing. Species with fast spreading stem derived clonal organs were favoured on pastures, whereas all other clonal growth forms and, particularly, non-clonal species were more abundant on meadows. More indicator species of wet soil conditions and species adapted to flooding were found on pastures. Grazing can be recommended as an alternative land use to mowing in contrast to abandonment, but a reduction in species richness and changes in species composition and species traits may occur.