Intermediate fen patches on a sloping rock outcrop in Koitelainen, Finnish Lapland

Abstract

Patches of intermediate fen, dominated by Molinia caerulea, Trichophorum cespitosum and Loeskypnum badium and resembling low aapa mire strings (lawn strings), were found on a sloping rock outcrop near the summit of Koitelainen Hill, central Finnish Lapland. Using eighteen 56-cm diameter plots and NMS-ordination we compared the vegetation of the patches to that of (A) corresponding larger fens belonging to a well-known north-Finnish mire site type Loeskypnum badium fen, (B) to that of narrow seepage soaks dominated by Warnstorfia sarmentosa, and (C) to that of a local heath patch. Ordination of the sample plots suggested a ‘horizontal gradient’ (general wetness) and three ‘vertical gradients’ (1: stability of the water regime; 2: poor-rich species; 3: frost action). Species richness increased along both the horizontal and the vertical gradient, from wet seepage areas to drier Loeskypnum badium fens, to intermediate fen patches and finally to the heterogeneous heath patch. We regard the fen patches of Koitelainen as belonging to an ecologically extreme group, the water-fluctuating lawn-fens. The water-fluctuating lawn-fens are characterised by a thin peat layer with high humification degree, caused by intermittent aeration during drought periods, as well as by the specific community composition, which is evidently partly structured by the seasonal drought tolerances of individual fen species.

Keywords

• boreal mire vegetation
• indicator species groups
• Loeskypnum badium
• seasonal drought
• vegetation gradient