ALNUS AS AN INDICATOR TAXON OF THE YOUNGER DRYAS COOLING IN EASTERN NORTH-AMERICA

The Younger Dryas cold interval (ca. 10.8-10 ka BP) in eastern North America has been documented throughout Atlantic Canada a parts of northeastern U.S.A. Due to differences in latitude and elevation between many of these sites, there is considerable regional variation in the nature of Younger Dryas pollen changes. However, there is a consistent peak in alder pollen percentages (generally 10-20%) at all these sites: A. crispa in Atlantic Canada and highland regions of northeastern U.S.A. and A. rugosa-type in lowland areas of New England. Macrofossil and pollen influx data show that the alder pollen percentage peak can be attributed to local and/or regional presence of alder populations at this time at several New England sites. The ecological significance of the Younger Dryas alder pollen percentage peak in Atlantic Canada is more difficult to explain. Evidence for two possible interpretations is discussed: (i) regional expansion of alder populations in the area, and (ii) alder populations were absent in Atlantic Canada at this time and the pollen originates from distant populations in New England.