LATE QUATERNARY VEGETATION DYNAMICS AND HYDROSERAL DEVELOPMENT IN A THUJA-OCCIDENTALIS SWAMP IN SOUTHERN ONTARIO

Palaeoecological data from a small swamp in southern Ontario are used to reconstruct postglacial upland and wetland vegetation dynamics and assess the relative importance of autogenic and allogenic factors in w etland development. The inferred upland forest dynamics are comparable in timing and trend with lake records from the region. During the ear ly Holocene, the shallow open water body became increasingly colonized by aquatic plants, until at around 8000 BP when the shallow open wate r community was replaced by a Larix swamp. At around 5600 BP, there wa s an apparent reversal in the wetland progression and Typha was locall y dominant. There is a possible hiatus in the sedimentary record at ar ound this time. Thereafter, a Thuja-Abies-Picea swamp community develo ped. The data suggest that internal factors and local events such as b eaver activity could be equally or more important than regionally acti ng factors such as climatic change in controlling the hydroseral progr ession. The changing nature of the wetland community led to a 40-fold variation in sediment accumulation rate during the Holocene, emphasizi ng the importance of establishing a good chronology and using a multip le-core approach in such systems.