A vegetation survey at Oil Well Bog, southern Ontario, suggested that the central Picea mariana - Sphagnum (black spruce swamp) community represented the most mature point in the wetland succession. Pollen analysis of short sediment cores from beneath three major communities in the wetland (black spruce swamp, white pine swamp, and low shrub swamp) showed that the black spruce community only became established in the last 100 years. From around 2000 BP, the wetland was dominated by low shrubs with a tall shrub element. Upland forest composition around the wetland changed around 500 BP, with a decrease in percentages of Fagus and an increase in Pinaceae. At the same time trees colonized parts of the wetland. When the upland forest was cleared by European settlers (ca. AD 1830-1845), low shrub communities reestablished, suggesting that initially the wetland surface became wetter. Over time, the present-day mosaic of swamp types began to develop. The pollen analyses showed that the black spruce swamp is present as a result of changes in the wetland hydrology induced by human activity, and the fragmentary low shrub vegetation community (which contains locally rare plant species) represents a relic of the pre-European settlement wetland community.Key words: paleoecology, wetland development, hydroseral succession.
Lithology and geochemistry of sediment cores, Pickering area, southern Ontario