PEATLAND DEVELOPMENT IN RELATION TO HOLOCENE CLIMATIC-CHANGE IN MANITOBA AND SASKATCHEWAN (CANADA)

Two peat cores from the southern boreal forest in south-central Manitoba and central Saskatchewan (Canada) were analyzed for microfossils, macrofossils, and physicochemical properties. Regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle Holocene. Pollen assemblages at the base of the Manitoba site indicate the presence of grassland-parkland vegetation in the area prior to 4230 BP. At the Saskatchewan site, boreal forest was present throughout the development of the peatland from before 5020 BP to present. Both the Manitoba and Saskatchewan records suggest a more open-deciduous character of the regional vegetation cover during the middle Holocene in the southernmost part of the expanding boreal forest, in comparison with the modern southern mixed-wood boreal forest. The presence of a Typha latifolia-dominated marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuations, likely due to frequent and severe periods of drought. Highest accumulation rates (1.24 mm peat/a, and 69 g carbon/(m2.a)) occur in the forested fen phase (4290-3710 BP) of the Saskatchewan site. Low accumulation rates (0.24 mm peat/a, and 12 g carbon/(m2.a)) in the bog phase (3710-960 BP) at this site are probably due to interruption of peat deposition or even surficial erosion of the deposits. Accumulation rates at the Manitoba site (4230-0 BP) are less variable, ranging from 0.30 to 0.82 mm peat/a and from 19 to 28 g carbon/(m2.a). Changes in accumulation rates at the Saskatchewan and Manitoba sites are not synchronous in spite of similarities in general development, indicating that, in addition to climate, local factors have played roles in the developmental histories of these peatlands.