Rehabilitation of Acidified Floating Fens by Addition of Buffered Surface Water

Floating fens are species‐rich succession stages in fen areas in the Netherlands. Many of these fens are deteriorating due to acidification; Sphagnum species and Polytrichum commune build 10–25 cm thick moss carpets, and the species diversity decreases. Earlier experiments in wet ecosystems indicate that successful restoration of circum‐neutral and mesotrophic conditions requires a combination of hydrological measures and sod removal. In an acidified fen recharged by rainwater in the nature reserve Ilperveld (The Netherlands), a ditch/trench system was dug for the purpose of creating a run‐off channel for acid rainwater in wet periods and to enable circum‐neutral surface water to enter the fen in dry periods. Moreover, the sod was removed in part of the fen. Ditch/trench creation or sod cutting had no effect individually, but a combination of the two measures led to a change in the abiotic conditions (higher pH and Ca), and in turn to an increase of species‐richness and the reestablishment of a number of characteristic species. Reestablishment of rare vascular plant species and characteristic bryophytes might be a long‐term process because of incomplete recovery of site conditions and constraints in seed dispersal.