Late Quaternary dynamics of tundra and forest vegetation in the southern Niagara Escarpment, Canada.

• Here, paleoecological studies from southern Ontario, Canada, are detailed to reconstruct vegetation history of the last 13 000 C year, with emphasis on late-glacial treeless vegetation. • Two sites (Crawford Lake and Twiss Marl Pond) were investigated using combined pollen and plant-macrofossil stratigraphic data. Comparison of multivariate analysis of pollen data with climate variations inferred independently from oxygen isotopes at the same site facilitated systematic evaluations of climate-vegetation interactions during different stages of vegetation development. • Pollen results show a distinctive successional change from Alnus - Dryas -Cyperaceae sparse tundra or periglacial desert to Salix - Juniperus -Cyperaceae dense tundra, with abundant arctic/alpine plant macrofossils, during the first few centuries after ice retreat. The area around the two sites was then dominated by Picea ( c. 12 000-10 000 C BP). Vegetation shifts, summarized by log-contrast principal component analysis of the pollen record, indicated a lagged response of forests to deglacial climate warming. The major vegetation shift at c. 7500 C BP from coniferous Pinus -dominated to mixed forests probably corresponded to a major shift from deglacial to full postglacial climates. Vegetation during the mid- and late Holocene responded more directly to natural (drought-triggered pathogen-induced Tsuga decline) and human disturbances (aboriginal and EuroCanadian settlements). • This study demonstrates that bedrock basins most faithfully recorded the earliest vegetation change because they usually experienced a short delay in lake formation after ice retreat.