Studies were undertaken to investigate the composition, structure and diversity of four different types of North Mongolian montane forest near the southern border of the taiga. These forest types, classified as willow-poplar, larch-birch, spruce-fir and Siberian-pine forests, were found to be significantly different with respect to the elevational gradient. In the study area, two fire regimes could be distinguished at lower and drier elevations, frequent surface fires resulted in less diverse forests comprising coniferous species, which in their adult form were found to be fire-resistant, burn-colonizing and light-demanding deciduous tree species. In contrast, the forests colonizing the moist, higher elevations and shaded slopes had a higher diversity of tree species with greater basal area, higher proportion of deadwood, and more regenerating trees; here the coniferous shade trees experienced infrequent but destructive treetop fires. Overall, our results showed that the four forest types differed in composition according to the tree species, diameter and height classes.