The vegetation of that part of the southern boreal forest which occupies the Cretaceous uplands in western Manitoba and central Saskatchewan has been studied, with particular attention to comnmunities in which Picea glauca (Moench) Voss is a component. As a background to the vegetational studies, the glacial and post-glacial history of the flora is first discussed, and it is argued that the boreal flora of this area probably survived the last glaciation along the southern and southwestern periphery of the continental ice sheet rather than in the Great Lakes refugium. The autecology of each of the eight principal tree species is examined as a basis for the understanding of their relative abilities to compete, survive and enter into the composition of the varlous forest types. The forest communities are sorted into serles based primarily on moistness of site, and within each series recognizable "noda" or "forest types" (in the Russian sense of the term) are defined by means of the dominant trees and by characteristic constant species of the undergrowth. The successional relationships of numerous communities are examined and it is concluded that very few can be designated as stable chiefly due to the frequency of fire whlch prevents development of the vegetation to a final steady state. However on extreme sites relatively permanent conmunitees occur, and on non-extreme sites where physiographic features provide protection from fires, fragments of the fundamental Abies and Picea/Hylocomium-Rubus forest type are found. An outline ls given of a generalized descriptive scheme which can be applied to all stands in the southern boreal forest. It is based on the physiognomy and moisture preferences of undergrowth species.