The interior forest of protected area(PA)recover quickly in terms of greater diversity and structural complexity than peripheral and outsides, which may be due to high plant-frugivore interactions in the interior forest than the disturbed outsides. To describe the structural and functional differences in tree communities from interior to outside forests with in small PA, we quantitatively analyzed the vegetation of Trishna Wildlife Sanctuary, a rich primate habitat of Northeast India. Vegetation was sampled at C10 cm girth at breast height by 10 m 9 500 m sized20 line transects(10 ha) laid in the interior(N = 7),peripheral(N = 7) and outside(N = 6) zones of this sanctuary. All transects were ordinated by Principal Component Analysis based on correlation between diversity and existing disturbance indices. We found significant differences(P 0.05) in taxonomic richness and diversity indices between the habitat. Van diagram confirmed greater unique species richness in the interior zone(64) than peripheral(28) and outside(6) zones. Overall density(ha-1) did not differed across the zones, but basal area(m2ha-1) was significantly(P 0.01) high in peripheral zone. Vertical distribution of stem density was linearly declined across zones(r2adj[ 0.70; P 0.01) with increase in the canopy height. Horizontal distribution of adult stems showed significant inverse quadratic relationship(r2adj[ 0.80; P 0.001), which suggests very low density of canopy forming voluminous trees in the interior zone.Immediate protection, restoration and management of interior regions are required to preserve local plant genetic diversity and also to maintain suitable habitat for threatened wildlife. The interior forest of protected area (PA) recover quickly in terms of greater diversity and structural complexity than peripheral and outsides, which may be due to high plant-frugivore interactions in the interior forest than the disturbed outsides. To describe the structural and functional differences in tree communities from interior to outside forests with in small PA, we quantitatively analyzed the vegetation of Trishna Wildlife Sanctuary, a rich primate habitat of Northeast India. Vegetation was sampled at C10 cm girth at breast height by 10 m 9 500 m sized20 line transects (10 ha) laid in the interior (N = 7), peripheral (N = 7) and outside (N = 6) zones of this sanctuary. All transects were ordinated by Principal Component Analysis based on correlation between diversity and existing disturbance indices. We found significant differences (P 0.05) in taxonomic richness and diversity indices between the habitat. Van map has greater unique species richness in the interior zone ( Overall density (ha-1) did not differed across the zones, but basal area (m2ha-1) was significantly (P 0.01) high in peripheral zones. Vertical Distribution of stem density was linearly declined across zones (r2adj [0.70; P 0.01) with increase in the canopy height. Horizontal distribution of adult stems showed significant inverse quadratic relationship (r2adj [0.80; P 0.001) low density of canopy forming voluminous trees in the interior zone.Immediate protection, restoration and management of interior regions are required to preserve local plant genetic diversity and also to maintain suitable habitat for threatened wildlife.