Diversity and pH changes after 50 years on the boreal mire Skattlosbergs Stormosse, Central Sweden

• The Skattlosbergs Stormosse min was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providinga unique opportunity to quantify long-term mire dynamics. The resultss how decreased pH in the richer (high-pH) parts of the mire, but little or no change in the poor fen andombrotrophipca rts.1 4 species had disappeared while two news pecies were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in lOm x 0Omp lots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 7 3 % of other bryophyt sepecies and 3 8% of vascular plant species had decreased by more than 20 % in plot frequency. There was a strong relationship between number of species and pH-value. The mean and standard eviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in morepolluted areas.

Nyckelord

acidification; floristic change; long-term study; species richness; succession; VEGETATION; NITROGEN; FENS; BOG; DEPOSITION; PEATLANDS; PLANTS; CANADA

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