Toward an Integrated Model for Raised-Bog Development: Theory and Field Evidence

Abstract

The development and distribution of Northern mires, including minerotrophic fens and ombrotrophic raised bogs, frequently are presumed to be strongly controlled by the interplay of regional climate and site geomorphology and history. Investigations of these relationships provide insights into long-term trends in ecosystem development by linking geological and landscape-scale processes. In this study, a theoretical model for raised-bog development integrates internal bog hydrodynamics with external factors, including local substrate characteristics, and regional temperature and moisture conditions. The model is used to interpret the development of raised bogs in the Bergslagen region, which coincides with the modern northern distributional limit of those mires in central Sweden. The development of minerotrophic fens that precede bog formation is also considered. Basal radiocarbon dates along surveyed transects are used to assess the pattern and timing of peatland formation and rates of lateral expansion. Previous palynological and lake-level studies from the same region provide independent evidence for changes in Holocene climate. Fen initiation in the region occurred throughout the Holocene under a broad range of environmental conditions. Once established, fens appear to expand faster during moister periods. Locally, substrate slope is an important mediator of fen development, with slopes >0.5% inhibiting lateral expansion. Accumulation of Sphagnum peat, an indicator of raisedbog initiation, occurred from -4000 to 5000 yr BP during relatively dry phases. Rates of lateral expansion were not significantly affected by increasing moisture or by decreasing temperatures until at least 2000 yr BP However, modern geographic trends in cross sectional shape of mires suggest that, at the northern limit of their range today, raised bogs are limited by low temperatures.