Aim:
To assess vegetation changes in montane fens and wet meadows and their causes over 38 years.
Location:
Wetlands in the Jura Mountains (Switzerland and France).
Methods:
Plots were inventoried in 1974 and re-located in 2012 (quasi-permanent plots) on the basis of sketches to assess changes in plant communities. The 110 plots belonged to five phytosociological alliances, two in oligotrophic fens (Caricion davallianae, Caricion fuscae) and three in wet meadows (Calthion, Molinion and Filipendulion). Changes between surveys were assessed with NMDS, and changes in species richness, Simpson diversity, species cover and frequency and the causes of these changes were evaluated by comparing ecological indicator values.
Results:
Changes in species composition varied between alliances, with a general trend towards more nutrient-rich flora with less light at the ground level. Species diversity declined, with a marked decreasing trend for the typical species of each alliance. These species were partly replaced by species belonging to nitrophilous and mesophilous grasslands. However, no trend towards drier conditions was detected in these wetlands. The greatest changes, with an important colonization by nitrophilous species, occurred in the Swiss sites, where grazing was banned 25 years ago. As a result of floral shifts, many plots previously belonging to fens or wet mesotrophic meadows shifted to an alliance of the wet meadows, generally Filipendulion. Moreover, communities showed a slight trend towards more thermophilous flora.
Conclusions:
The investigated wetlands in the Jura Mountains have suffered mainly from eutrophication due to land-use abandonment and nitrogen deposition, with a loss of typical species. Areas with constant land use (grazing or mowing) showed less marked changes in species composition. The most important action to conserve these wetlands is to maintain or reintroduce the traditional practices of extensive mowing and livestock grazing in the wetlands, especially in areas where they were abandoned 25 years ago. This previous land-use change was intended to improve fen conservation, but it was obviously the wrong measure for conservation purposes.