The palaeoecology of a treed bog in western boreal Canada: a study based on microfossils, macrofossils and physico-chemical properties

Abstract

The developmental histories of a wetland and the surrounding upland vegetation in the southern boreal region of western Canada are traced through microfossil, macrofossil, physico-chemical and radiometric analyses of a 425 cm deep core consisting of sandy gyttja and peat. Microfossil analysis includes algal, fungal and zoological ‘Types’ which are illustrated and described, with notes on their occurrence as observed in several peat sequences of western boreal Canada. Local wetland development started in the central area of a 65 ha closed depression at c. 5000 BP, due to a rise in the groundwater table related to a gradual increase in effective precipitation in the region. Initial stages were characterised by Typha-dominated marsh communities that suggest marked seasonal fluctuations in local water levels. The accumulation of organic matter could not keep pace with the ever-rising groundwater table, and a shallow eutrophic pond with aquatic macrophytes developed locally. The body of open water was surrounded by marsh vegetation that was gradually being displaced towards the margins of the depression. At 4330 BP moist conditions became prevalent throughout the growing season. A brown-moss dominated treed rich fen replaced the shore marsh community and gradually began to encroach on the small pond. The basin completely terrestrialised at 3260 BP. Autogenic processes caused by peat accumulation resulted in a transition towards a Sphagnum-dominated treed poor fen. At 2790 BP a treed bog became established, firstly dominated by Sphagnum angustifolium and S. magellanicum indicating moist local conditions. After 1870 BP S. fuscum became dominant, indicating drier conditions locally. The upland vegetation just before local wetland formation was characterised by Picea in relatively wet depressions and by Populus in drier areas. Some grassland patches were present, most probably on the more southerly exposed slopes of the hills. Picea was locally displaced by wetland vegetation at c. 5000 BP, whereas deciduous forest and some grassland stands continued to dominate the surrounding hills. The coniferous taxa Pinus and Picea began to invade the uplands after 4330 BP, contemporaneously with the development of the local peatland. This marks the time at which the modern southern boreal ecosystem dominated by peatlands in lowlands and mixed wood forest in uplands became established in the area.