Age Structure and Regeneration Dynamics of Sugar Maple at the Deciduous/Boreal Forest Ecotone, Ontario, Canada

Abstract

Sugar maple reaches its northern limit along the eastern shore of Lake Superior marking the transition from the deciduous forest of eastern North America to a predominantly boreal forest community. In light of regional warming trends over the past 100 years and projections for even warmer conditions in the future, we sought to characterize the current age structure and regeneration status of both sugar maple and boreal tree species within this ecotone zone. Within Lake Superior Provincial Park (Ontario, Canada), a series of east-west trending hills create numerous deciduous-boreal transition zones as sugar maple occupies uplands and boreal species occupy valley bottoms; then, once north of the sugar maple limit, boreal species dominate all topographic positions. Unlogged forest stands were sampled in the transition zone on ridges and slopes both north and south of the sugar maple limit. Overall tree density and basal area in sugar maple and boreal stands were similar across the ecotone, but seedling density was significantly higher in plots dominated by sugar maple. Moreover, sugar maple seedlings, but not saplings, were found slightly beyond the adult sugar maple tree hillside limit, indicating that the potential for range expansion may be limited by microclimatic variables, namely cold air drainage.