Pre-European settlement conditions and human disturbance of a coniferous swamp in southern Ontario

A vegetation survey at Oil Well Bog, southern Ontario, suggested that the c entral Picea mariana - Sphagnum (black spruce swamp) community represented the most mature point in the wetland succession. Pollen analysis of short s ediment cores from beneath three major communities in the wetland (black sp ruce swamp, white pine swamp, and low shrub swamp) showed that the black sp ruce community only became established in the last 100 years. From around 2 000 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 t ime trees colonized parts of the wetland. When the upland forest was cleare d by European settlers (ca. AD 1830-1845), low shrub communities reestablis hed, suggesting that initially the wetland surface became wetter. Over time , the present-day mosaic of swamp types began to develop. The pollen analys es 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 sh rub vegetation community (which contains locally rare plant species) repres ents a relic of the pre-European settlement wetland community.