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 ground water flow pattern is remarkably similar. Paleoecological 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.

Summary 1The influence of tephra (aerially transported volcanic ejecta) on mire vegetation was investigated in a field experiment at Sarobetsu Mire, northern Hokkaido, Japan, which simulated relatively thin, widespread tephras. It was carried out in the centre of a raised part of the mire in a Carex middendorffii -Sphagnum papillosum community. 2 We tested the effects of varying tephra layer thickness, grain size and season of the simulated tephra impact. 3 Vegetation surveys and analyses of the mire pore water were carried out before and 1 and 2 years after tephra application. Redox potential, oxygen saturation and sulphide concentration were measured in the surface layer of selected plots after 10 months. 4 Pore water chemistry and oxygen saturation changed significantly in some treatments. Some plant species disappeared from certain treatments after tephra application, but the majority survived. Colonization by non-mire species played a significant role in only one treatment. Mosses were more strongly affected by the disturbance than vascular plants. 5 Tephra had stronger effects on the vegetation when layers were thicker, were more fine-grained and when applied at the beginning rather than at the end of the growing season. 6 Moderate tephra deposition is unlikely to cause long-term changes in mire development. Subsequent succession depends on properties of the tephra, on the vegetation type (e.g. life-forms) and on the season, but the original vegetation will probably recover even where the moss layer is severely damaged, as Sphagnum spp. can re-establish by growing through tephra at least up to 6 cm thick.

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