Old-Age Fen Ecosystems; their Loss of Biodiversity and Management Options. 65 Years of Succession Recorded in Ilperveld (NL)

Abstract

A fen area north of Amsterdam used to be rich in plant species but changed into a monotonous acidic Sphagnum-Polytrichum-moss-layer over the last 50 years. Species loss was greatest after ca. 1975 and was attributed to acid rain, a big environmental problem at that time. We reviewed data over 1942–2010 to describe the succession and processes in this fen system. Acidic conditions were already present in 1942 and yet many red list species were present. Reconstructing chemical soil and water data indicated a gradual process of acidification in the subsoil, caused by increasing raft depth which enhanced the storage of acidic rainwater. Buffering capacity of the subsoil was consequently gradually depleted resulting in the loss of many (endangered) plant species. Changes in salinity or nutrient concentrations were considered of less importance to the succession of this fen system. Conservation and restoration of biodiversity in these wetlands, as obliged by the Habitat- Directive, is impossible unless the succession can start again from open water facilitating plant species of high nature value in the long term.