Effects of winter mowing on vegetation succession in a lakeshore fen

摘要

To assess whether winter mowing in wetlands fulfils the aim of preventing succession towards drier communities, 34 permanent quadrats (15 m(2)) were surveyed annually from 1984-1985 to 2000 within large mown and unmown (control) areas (several ha) in a calcareous lake shore fen (W Switzerland). Three trends were noticed: decrease of aquatic species, spread of Cladium mariscus and establishment of woody species (especially Alnus glutinosa and Frangula alnus). None of these trends was prevented by mowing, but mowing did prevent the accumulation of C. mariscus litter and kept woody saplings small. Succession was generally slow and often occurred in the form of sudden, discrete changes. Plant species richness increased with mowing and remained constant without mowing. Soil disturbance by the mowing machine contributed more to the effects of management on species composition than the periodic removal of biomass. It is concluded that mowing every three years in winter is insufficient to preserve semi-aquatic communities against succession but sufficient to maintain the plant species richness of a low productive, regularly flooded fen.