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The present paper introduces and describes a poorly known wetland type – aro wetland – in well permeable mineral soil substratum in Northern Ostrobothnia and Kainuu (between 64° – 66° N lat.). Field observations (linked with the interpretation of aerial photographs) were made in 32 localities, whose conservation status is presented. We define boreal aro wetlands ecologically as a seasonal wetland type of their own which occur on well-drained mineral soil, which are mainly characterised by treeless, mire expanse fen vegetation and in which the peat accumulation is (almost) totally hampered by the vigorous decomposition of the organic matter resulting from an extremely unstable water regime (flood and seasonal drought) and small plant production. Aro wetlands in the western part of the study area occur on sandy substratum (the largest in parts of mire complexes split by ancient raised beach ridges), whereas in the eastern part the aro wetlands known so far are small pond-like depressions in till substratum. Carex lasiocarpa (mostly) dominates the vegetation on sandy substratum. Juncus filiformis and Carex nigra are typical, and Rhynchospora fusca and Molinia caerulea a bit rarer. Sphagnum cover is usually minimal. Considering aro wetlands an extreme case of suo (mire) makes the stability of water regime (stable – unstable) a direction of variation in the traditional Finnish mire site type system, which is based on several ecological gradients.
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Laitinen,
University of Oulu, Department of Biology, Botany, P.O.Box 3000, FI-90014, Finland
Sähköposti:
ei.tietoa@nn.oo
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Rehell,
Sähköposti:
ei.tietoa@nn.oo
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Huttunen,
Sähköposti:
ei.tietoa@nn.oo
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Eurola,
Sähköposti:
ei.tietoa@nn.oo
