This study provides a general description and mapping of hemi-arctic subzones and ecoclimatic regions lying between Hudson Bay and Ungava Bay in Nouveau-Québec. Dis-tinctive distributions of dominant tree species (white spruce, black spruce and tamarack) and also of the main coniferous formations were mapped in order to provide ecological subdivisions of this territory. Data suggest that present and historical climatic factors are responsible for the nature and the specific pattern of the proposed ecological limits.