Plant species diversity along an altitudinal gradient in Simbalwara wildlife sanctuary, Himachal Pradesh

The composition of forest vegetation along an altitudinal gradient (400 to 650m) in Simbalwara Wildlife Sanctuary was studied during August, 2003. The forest is composed of 53 species of trees, 32 of shrubs and 175 of herbs. The plant communities identified at 400-525m and 525-650m elevation range were Shorea robusta – Mallotus philippensis and Shorea robusta – Terminalia alata respectively. On the basis of importance value index (IVI), Shorea robusta was the dominant tree species at both the elevation ranges. The distribution pattern of plant species was random and contiguous at both the altitudes. The concentration of dominance was lower and index of diversity higher for plant species at both the altitudes Index of diversity for trees was 4.390 and 3.942 at 400-525m and 525-650m elevation range respectively. The index of similarity for trees, shrubs and herbs between two altitudes was 0.64, 0.65 and 0.54 indicating remarkable degree of similarity in plant species. The population structure of tree species is represented mainly by two patterns, one represented by greater proportion of individuals in seedlings stage indicating frequent reproduction and another indicating more individuals in intermediate girth classes with absence of seedlings. If the latter trend continues for longer period, the species may disappear from the area in near future.