Hydrological landscape settings of base-rich fen mires and fen meadows: an overview

Question: Why do similar fen meadow communities occur in different landscapes? How does the hydrological system sustain base-rich fen mires and fen meadows? Location: Interdunal wetlands and heathland pools in The Netherlands, percolation mires in Germany, Poland, and Siberia, and calcareous spring fens in the High Tatra, Slovakia. Methods: This review presents an overview of the hydrological conditions of fen mires and fen meadows that are highly valued in nature conservation due to their high biodiversity and the occurrence of many Red List species. Fen types covered in this review include: (1) small hydrological systems in young calcareous dune areas, and (2) small hydrological systems in decalcified old cover sand areas in The Netherlands; (3) large hydrological systems in river valleys in Central-Europe and western-Siberia, and (4) large hydrological systems of small calcareous spring fens with active precipitation of travertine in mountain areas of Slovakia. Results: Different landscape types can sustain similar nutrient poor and base-rich habitats required by endangered fen meadow species. The hydrological systems of these landscapes are very different in size, but their groundwater flow pattern is remarkably similar. Paleo-ecological research showed that travertine forming fen vegetation types persisted in German lowland percolation mires from 6000 to 3000 BP. Similar vegetation types can still be found in small mountain mires in the Slovak Republic. Small pools in such mires form a cascade of surface water bodies that stimulate travertine formation in various ways. Travertine deposition prevents acidification of the mire and sustains populations of basiphilous species that elsewhere in Europe are highly endangered. Conclusion: Very different hydrological landscape settings can maintain a regular flow of groundwater through the top soil generating similar base-rich site conditions. This is why some fen species occur in very different landscape types, ranging from mineral interdunal wetlands to mountain mires