Abstract: The structure of thirteen forest communities from 700～1900m along the northern slope of Changbai Mountain was studied. The results showed that composition of dominant tree species and layer structure displayed the transitional tendency from complexity to simplicity with the increase of elevation. The proportion of coniferous species obviously increased and broad-leaved trees decreased from elevation 700～1700m. At timberline, coniferous and broad-leaved species sharply decreased and species obviously subrogated along altitude gradient. The peak value of average DBH and basal area in the community appeared at elevation segment of 900～1100m and 1600m. The two elevation segments were exactly the transitional zone of different forest communities. Except for Betula ermanii forest at 1800m, the structure of diameter class in other communities took on toppled “J" Shape. Namely, among tree species of each diameter class, updated seedlings and saplings predominated quantitatively. With the increase of DBH, the numbers of stumpage decreased gradually. The structure of diameter class showed that communities at each elevation on the northern slope of Changbai Mountain updated well and communities were in the status of stable development.

Key words: Plutella xylostella, Cotesia plutellae, Oomyzus sokolowskii, Interspecific interaction