THE RECENT DEVELOPMENT OF A MIXED SHRUB AND CONIFER COMMUNITY ON A RAPIDLY EMERGING COAST (EASTERN HUDSON-BAY, SUB-ARCTIC QUEBEC, CANADA)

This paper presents an analysis of the relation between shrub mat deve lopment and the expansion of conifer forest margins over a rapidly eme rging coast (average rates ranging between 1.1 and 1.5 cm/year) in res ponse to postglacial isostatic adjustment. Shore emergence stimulates the downward expansion of shrub communities on shore (mostly willow) t hat form dense mats acting as snow traps protecting conifer seedlings on shores. Conifer population structures and tree rings indicate three phases in the forest margin expansion process: (1) an initial period of slow growth and juvenile sparse stands controlled by shrub mat dist ribution and densities, (2) a phase characterized by denser conifer ma ts, and growth release of above shrub stems, and (3) a final phase of maturation dominated by a vegetative regeneration process (clones) and regressive growth forms, highly controlled by the shore climatic cond itions.