POSTGLACIAL PALAEOPHYTOGEOGRAPHY OF THE EASTERN ST-LAWRENCE-RIVER WATERSHED AND THE CLIMATIC SIGNAL OF THE POLLEN RECORD

Pollen analytical studies of the sediments of over 150 lakes and bogs in southern Quebee have led to the identification of a limited number of sequential types or temporal suites of the various pollen assemblag es within each of three main stages of the postglacial development of vegetation: the Non-arboreal stage, the Afforestation stage and the Fo rest stage. These sequential types, within any of the three stages, sh ow distinct geographical and chronological distributions in southern Q uebec during the last 12,000 yr. When compared in a broader geographic context, they demonstrate a strong differentiation of the pollen reco rd within and around the Great Lakes-St. Lawrence River Watershed duri ng the last 15,000 yr B.P. Amongst the most striking gradients identif ied stand the late-glacial peri-champlainian gradients (ca. 11,500-10, 000 yr B.P.) and the early Holocene gradients. The former involve seaw ard and northeastward clines from closed coniferous forests to tundras , and the latter, northeastward changes in the nature and duration of the Afforestation stage. The modem pattern of even the broader vegetat ional gradients in southern Quebec was not attained before 3000 yr B.P . Palynological reconstruction of the various regional paleoclimates h ighlights the interaction of local, regional and global climatic forci ngs through time. Mesoscale climate modelling and palaeoclimatology sh ould find boundary conditions in those regional reconstructions.