A rapid reconnaissance technique was used to sample montane vegetation in the Alsek River region, southwest Yukon. Twenty-one major community types are described from 223 sample stands. The forest vegetation of the region is interspersed with numerous shrub and herb vegetation types. This vegetation diversity is extraordinarily rich for a forest region and is due primarily to the variable climate (both local and regional) and the frequency of disturbance by fire and geomorphological processes.Ten communities, within four forest types, are distinguished in the region. The most widespread forest type is dominated by Picea glauea. The remaining three are dominated by Populus tremuloides, P. balsamifera, and Salix scouleriana. Shrub communities recognized include the Betula glandulosa – Festuca altaica, Salix glauca, Juniperus communis – Arctostaphylos uva-ursi, Artemisia frigida – Poa glauca, Artemisia alaskana, and Salix setchelliana – Oxytropis campestris types. Herb communities distinguished include the Carex sabulosa, Hedysarum boreale – Agropyron yukonense, Calamagrostis, and Agropyron yukonense types.Examination of diversity and its components during succession in the Alsek River region indicates that, in general, richness and general diversity increase and dominance decreases until the later stages of succession, when these trends are subsequently reversed. Evenness, while somewhat more variable, showed trends similar to that of the dominance component. Deviations from these trends occurred when the habitat was either extremely homogeneous or extremely heterogeneous.The flora of the region is relatively rich and derived from many North Temperate elements. The largest segment (64%) is derived from the more northern (Circumarctic-alpine, Circumboreal-montane, Amphi-beringian, Amphi-atlantic) elements.