IMPACT OF THE YOUNGER DRYAS COOLING EVENT UPON LOWLAND VEGETATION OF MARITIME CANADA

The aim of this research is to determine the response of the vegetatio n in coastal Maritime Canada to the Younger Dryas cooling event (appro ximate to 10 800-10 000 C-14 yr BP) that interrupted the warming trend following the last glaciation. Detailed paleoecological studies were carried out on the organic, pollen, and plant macrofossil content of s ediment cores recovered from six small lakes in New Brunswick and Nova Scotia. Results show that there was regional variation in the vegetat ion response to the cooling. Records from Splan Pond, Mayflower Lake, and Little Lake show a change from boreal forest or woodland to shrub- tundra as a result of the cooling, while Lac a Magie shows floristic c hanges of shrub-tundra, and Chase Pond and Main-a-Dieu Pond show repla cement of shrub-tundra by herb-tundra in response to the Younger Dryas . The climate warming signifying the end of the Younger Dryas caused s uccession from shrub-tundra to boreal forest, or from herb-tundra to s hrub-tundra. Macrofossil evidence of arctic/alpine species such as Dry as integrifolia, Salix herbacea, and Cassiope hypnoides attests to the severity of the Younger Dryas cooling. Vegetation changes in response to the climate cooling and warming, marking the onset and termination of the Younger Dryas respectively, were very rapid, taking only 50-10 0 yr. However, the response of some taxa, such as dwarf birch, appears to have lagged the onset of the climate change by several decades, al though the duration of the lag varies between sites.