Restoration experiments in middle European wet terrestrial ecosystems: an overview

Most wetlands in the central European lowlands have been severely altered by cultivation. As a consequence they no longer fulfil their function as habitats for specialised species and communities, nor as retention areas for water and solid materials. Therefore, a number of renaturation experiments are in progress, which intend to develop and test strategies and measures to improve this defect in landscape diversity. For this purpose experiments on re-wetting, nutrient depletion of eutrophicated areas and re-establishment of typical wetland plant species and phytocoenoses have been performed. An ecological development concept defining the aims and describing their feasibility precedes such experiments. Preliminary results indicate that the reconstruction of the former state (regeneration) is impossible within reasonable time spans. In drained raised bogs overgrown with heather, as well as in those which have been industrially exploited, the primary aim must always be to restore efficient peat formation as far as possible; as a rule one succeeds only with well-growing and nutrient-demanding fen and transitional bog species. In cultivated fens the aim is to reduce peat loss. As a first step this is accomplished by converting arable fields and sown meadows into permanent grassland, if possible with reduced fertilization and low mowing or grazing frequencies, and accompanied by rewetting during winter. Many experiments have sought to impoverish eutrophicated fen soils and introduce typical fen species by sowing or planting, so well tested techniques are available. However, the total prevention of peat loss is only possible by permanent rewetting throughout the year, so that peat accumulation can start again. Only in this way could fens regain their former function as sinks in landscape processes.