Four decades of vegetation development in a percolation mire complex following intensive drainage and abandonment
Background: Many minerotrophic fens in Central Europe have undergone similar sequences of land-use transformation. Drained and used as meadows or pastures for decades in the twentieth century, they were abandoned in the 1990s due to changes in agricultural economics. This sequence of land-use change has a severe impact on vegetation and is likely to initiate secondary succession and is possibly leading to an impoverishment in species diversity and to taxonomic homogenisation.
Aims: We assess the impact of agricultural use and subsequent abandonment on vegetation composition in a percolation fen in north Germany and characterise successional changes and changes in abiotic site conditions.
Methods: In 2010, we resampled 77 plots of a phytosociological survey from 1967–1970 in a lowland percolation mire complex in the lower Recknitz valley, north-east Germany. These included three characteristic vegetation types of percolation fens. To investigate and quantify vegetation changes we used dissimilarity measures, diversity metrics and ecological species indicator values.
Results: Overall species richness declined only slightly while there was a more pronounced decrease in species richness at the plot level in all recorded vegetation types, resulting in increased beta diversity. Generalist and nitrophilous species increased in abundance, indicating ongoing succession.
Conclusions: Drainage for agricultural use and subsequent abandonment has long-lasting effects. Altered hydrological and nutrient status of the fen soil has initiated secondary succession. There is indication of an extinction debt that in the future may lead to an impoverishment of species diversity in the area. Conservation of open mesotrophic fen species may thus only be achieved if moderate use is continued and hydrologic conservation measures are applied on wide contiguous areas.