Medium-term changes of vegetation composition on fens of the rural landscape, tested using fixed permanent plots

Sedge-moss fens are declining and are being replaced by more productive ecosystems in agricultural landscapes as a result of changes in the way how the landscape is used by society. We aim to identify commonalities between changes in vegetation species composition and changes in properties of groundwater on fens. Most similar resurvey studies use non-permanent or semi-permanent plots, while medium-term studies from fixed permanent plots are scarce. We studied fifteen years of change in vegetation composition within thirty permanent 4 x 4 m plots established in 2004 on fifteen sedge-moss fens in the eutrophicated landscape of the Trebon Basin (Czech Republic, Central Europe). Complete species composition and abundance data, covers of the moss, herb and shrub layers, the mean and maximum height of the herb layer, and water chemistry and water level data were collected in 2004 and 2019 by the same person, and potential changes between 2004 and 2019 were tested. We found a significant compositional change between the two periods within poor and moderately rich fens, with an increasing abundance of woody plants, tall sedges, tall grasses and some fast-growing Sphagnum mosses. The same changes were observed on flooded and rich fens but were insignificant. Increasing ammonium concentrations in initially relatively ammonium-poor fens, a generally decreasing ratio between ammonium and nitrates, and declining water levels accounted significantly for the observed changes in composition. Species richness generally increased because of an increase in matrix-derived non-fen species whereas specialist species decreased in cover. Although massive environmental and compositional changes occurred before 2004, they continued between 2004 and 2019. Intensification of conservation management or reduction of pond farming is therefore needed.

Automated summary

Sedge-moss fens are declining in agricultural landscapes due to changes in landscape use, leading to a shift in vegetation composition and properties of groundwater. Permanent plots were used to study changes over fifteen years on fifteen fens. Results showed significant compositional changes in poor and moderately rich fens, with an increase in woody plants, tall sedges, tall grasses, and fast-growing Sphagnum mosses. Increasing ammonium concentrations, decreasing ammonium to nitrate ratio, and declining water levels contributed to the observed changes. Conservation management or reduction of pond farming is needed to address these changes.