The region is characterized by its boreal vegetation and unusually diverse and pristine habitats. It includes one of the largest remnants of substantially undisturbed old-growth forest in the upper Great Lakes region (including the Porcupine Mountains, the Sylvania Tract, and the Boundary Waters Canoe Area). Forests on the uplands are dominated by hemlock and northern hardwoods. Forests on the steep slopes and mountain ridges are dominated by pine-oak stands.