Abstract
We studied 45 mid-boreal wetlands in a rugged land uplift coast with a thin cover of till. Wetlands ranged from 1 to 53 m a.s.l. and were of highly various sizes. Our aims were to examine, if vegetation types are valid in comparing wetlands, what kind of ecological major pattern the vegetation type composition of wetlands shows and how vegetation types distribute across altitudes. On those ground we discuss the wetland succession of the study area. We used the Finnish mire site types as vegetation types. Mire site types could be used for an ecological classification and ordination of the wetlands. As was expected, the major gradient consisted of the transition from mire margin (swamp) to expanse. The distribution of the Major Vegetational Wetland Groups (MVWG) responded to a general water-flow pattern in the landscape. Partly different peatland succession sequences occur in areas with small mire basins and in areas with larger mire basins with evolving mire complexes. Sequences of small wetlands and those of mire complexes follow the same trajectory only as far as the major gradient is considered while they differ with regard to the vegetation type composition of locally rare vegetation types and with regard to peatland morphology. Trajectories of mire complexes at catchment divides differ from those at catchment centers where the waters in the landscape tend to gather. Peatland forms of aapa mires experience a change reaching altitudes of 30–50 m a.s.l. Small bog complexes at catchment divides reach a stage of an unpatterned Sphagnum fuscum bog in the study area. Mature mixed complexes with aapa-mire parts and patterned sloping-bog parts only occur at altitudes higher than 60 m a.s.l. Peculiarities in the succession of the wetlands of Nyby, which include the presence of separate incomplete successional sequences in the same area, are mainly caused by the peculiar topography with various sub-areas and with an abundance of rock outcrops.
Highlights
Boreal landscape is characterized by coniferous forests and peatlands
Bedrock topography determines the major lines for landforms, including the size and proportion of depressions occupied by wetlands in the emerging landscape, and topographically different coasts provide different prerequisites for wetland succession
Similarity of certain degree was found between the current spatial vegetation gradient in peatland succession and the vertical temporal vegetation gradient observed in the oldest peatland in the same study area
Summary
Boreal landscape is characterized by coniferous forests and peatlands. From south- to mid-boreal (Hämet-Ahti 1981) lowlands around the northern part of the Baltic Sea, the Gulf of Bothnia, new landscape is emerging from the sea as a result of the glacio-isostatic land uplift. Bedrock topography determines the major lines for landforms, including the size and proportion of depressions occupied by wetlands in the emerging landscape, and topographically different coasts provide different prerequisites for wetland succession. This has not been much stressed in botanical peatland studies in general. Recent investigations for conservation purposes in Finland (Kaakinen et al 2008) and partly old work (Aario 1932) concentrate on the vegetation and succession of mires in median to large bedrock basins with evolving mire complexes, while the vegetation and the succession of mires in small depressions are partly ignored (see Lindholm 2013a) This implies that possible differences between the succession of small wetlands among rugged topography and the succession of wetlands into mire complexes among flatter topography are not studied. Walker et al (2010), warn of a false use of chronosequences stating that they are often used inappropriately, leading to false conclusions about ecological patterns and processes
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