Measuring the efficiency of fen restoration on carabid beetles and vascular plants: a case study from north-eastern Germany

The aim of the study was to assess the effects of fen rewetting on carabid beetle and vascular plant assemblages within riverine fens along the river Peene in north-eastern Germany. Drained (silage grassland), rewetted (restored formerly drained silage grassland), and near-natural (fairly pristine) stands were compared. Eighty-four beetle species (7,267 individuals) and 135 plant species were recorded. The richness of vascular plant species and the number of endangered species were highest on near-natural fens. Fourteen years of rewetting did not increase plant species numbers compared with drained fens. For carabid beetles, however, species richness and the number of stenotopic species were highest on rewetted fens. Rewetting caused the replacement of generalist carabids by wetland specialists, but did not provide suitable habitat for specialist fen carabids or for plant species of oligo- or mesotrophic fen communities. Therefore, raising the water table on fens with nutrient-rich, degraded peat was not sufficient for restoring species assemblages of intact fens, although water level was the most important environmental factor separating species assemblages. Our study illustrated that insects and plants may respond differentially to restoration, stressing the need to consider different taxa when assessing the efficiency of fen restoration. Furthermore, species assemblages of intact fens could not be restored within 14 years, highlighting the importance of conserving pristine habitat.