Holocene development and peat growth of the raised bog Pesaensuo in southwestern Finland

摘要

The natural history of the Pesaensuo raised bog (60 deg 46.2' N, 22 deg 56.7' E,87 m a.s.l.) was studied using both biotic and abiotic palaeoecological methods including 211 radiocarbon dates. Peat formation commenced on a centrally domed clay bottom with primary mire formation at about 8300 C-14 years BP (ca. 9200 cal BP), with a contribution made by subsequent forest fires. Peat growth in the Carex peat section and at the end of the minerotrophic stage was approximately equal both in the bog center and at the margin. In the Sphagnum peat section, a phase of divergent growth is evident. During the last two thousand years, peat growth has been slow (average 0.22 mm/yr). The cumulative mass versus age curve for the bog center shows a slightly convex trend, while the depth versus mass trend is linear, both of which contradict the concave plot predicted for age against depth by Clymo's model of peat growth. The alternation of thin highly humified streaks and slightly humified peat in the peat strata resembles short-cycle Sphagnum fuscum regeneration. The thicker highly humified layers correlate with slow peat growth and the dry phase in the hydrology of the bog. The stratigraphical and hydrological changes observed were influenced more by the natural succession and local phenomena, such as fires than by climatic factors