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 o f 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 locati ons, providing a unique opportunity to quantify long-term mire dynamics. The results show decreased pH in the richer (high-pH) parts of the min, but Little or no change in the poor fen and ombrotrophic parts. 14 species had disappeared while two new species were recorded. Most species had a more r estricted distribution in the mire area in 1995 than in 1945. Species richn ess in 10m x 10m plots had decreased, especially in plots with higher pH. M ost Sphagnum species had unchanged distributions over the mire, while 73% o f other bryophyte species and 38% of vascular plant species had decreased b y more than 20% in plot frequency. There was a strong relationship between number of species and pH-value. The mean and standard deviation 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 depo sition. The mire represents an almost untouched site which can set as a ref erence for mires in more polluted areas.