TOWARD AN INTEGRATED MODEL FOR RAISED-BOG DEVELOPMENT - THEORY AND FIELD EVIDENCE

The development and distribution of Northern mires, including minerotr ophic fens and ombrotrophic raised bogs, frequently are presumed to be strongly controlled by the interplay of regional climate and site geo morphology and history. Investigations of these relationships provide insights into long-term trends in ecosystem development by linking geo logical and landscape-scale processes. In this study, a theoretical mo del for raised-bog development integrates internal bog hydrodynamics w ith external factors, including local substrate characteristics, and r egional temperature and moisture conditions. The model is used to inte rpret the development of raised bogs in the Bergslagen region, which c oincides 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 survey ed transects are used to assess the pattern and timing of peatland for mation and rates of lateral expansion. Previous palynological and lake -level studies from the same region provide independent evidence for c hanges in Holocene climate. Fen initiation in the region occurred thro ughout the Holocene under a broad range of environmental conditions. O nce 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 Sphagn um peat, an indicator of raised-bog initiation, occurred from approxim ate to 4000 to 5000 yr BP during relatively dry phases. Rates of later al 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 lo w temperatures.