RADIOCARBON EVIDENCE FOR RATES OF LATERAL EXPANSION IN RAISED MIRES IN SOUTHERN FINLAND

Radiocarbon ages from the bottom peat deposits and detailed morphometric measurements at five peatlands in the boreal region of southern Finland were used to reconstruct the Holocene patterns of raised mire development. The results suggest that the areal expansion of the mires has been extremely rapid at times-up to several hundreds hectares per millennium-but the periods of more rapid expansion were not coincident among the mires. The rate of lateral extension was shown to depend mainly on the topography of the mineral substrate. Horizontal expansion did not always correlate with vertical growth. Mires expanded slowly between ca. 6000 and 4000 yr B.P., probably as a consequence of drier climatic conditions at that time. The mires also expanded slowly during the two to three recent millennia, the reason for this most probably lying in steepening of the bottom gradient toward the marginal areas of the present mires. The results point to a substantial measure of local environmental control over the lateral extension in raised mire ecosystems. (C) 1994 University of Washington.