Climatic change causes abrupt changes in forest composition, inferred from a high-resolution pollen record, southwestern Quebec, Canada

A pollen profile from a lake with varved sediments sampled at continuous 10-year intervals and spanning the past 1000 years was analyzed to understand the effects of climate change and anthropogenic activity on forests in southwestern Quebec. Pollen assemblages were dominated by arboreal taxa, primarily Pinus, Tsuga, Betula and Fagus. Between 990 and 1560 AD, pollen accumulation rates and percentages of hardwoods (Betula, Fagus, Acer, Ulmus, Tilia) and Tsuga were relatively high. At 1560 AD, PARs of many hardwood taxa (Fagus, Acer, Betula, Fraxinus, Ulmus) and Tsuga abruptly decreased, some remaining low for the remainder of the record (Tsuga, Fagus, Acer), but others increasing after 50 years (Betula, Fraxinus). An increase in non-arboreal pollen between 1810 and 2010 AD was caused by European settlement of the area. The transition in the pollen assemblages beginning at 1560 AD and a climate reconstruction based on these data shows an abrupt climate cooling had a significant impact on the pollen accumulation rates of the region within a couple of decades. A synthesis of this record with other high-resolution and well-dated pollen data from the conifer-hardwood forest of eastern North America shows consistent results across the whole area, indicating that very-high resolution pollen data can provide insight into multi-decadal climate variability and its impact on forest vegetation.