Lalfakawma et al.: Community composition and tree population structure in undisturbed and disturbed tropical semi- Abstract Species composition, density, importance value index, diversity, dominance and tree population structure were studied in disturbed and undisturbed stands of tropical semi-evergreen forest in Lunglei District of Mizoram, North-East India. Total number of species in the undisturbed stand was 67 while in the disturbed stand 63 species were recorded. Number of tree and shrub species in the undisturbed stand were higher (32 and 18) than the disturbed stand (17 and 16). However, the number of herbaceous species remained higher in the disturbed stand (30) compared to the undisturbed stand (17). Castanopsis tribuloides (Smith) was common in both stands, and showed dominance in the undisturbed stand with a density of 90 individuals' ha -1 . However Schima wallichii (DC.) Korth Choicy was dominant in the disturbed stand with a density of 125 individuals' ha -1 . In both stands higher dbh classes showed lower density than that of the lower and intermediate girth classes. In general, the undisturbed forest stand showed more density of trees in each dbh classes and the intermediate girth class in particular. The study reveals that the anthropogenic disturbance causes disruption of forest structure and changes community composition which ultimately leads to disruption of tree population structure.