Ecology, Environment and Conservation Paper

TREE SPECIES RICHNESS, POPULATION STRUCTURE AND REGENERATION STATUS ALONG THE DISTURBANCE GRADIENT IN TROPICAL FORESTS OF SOUTH TERRITORIAL DIVISION, SIKKIM, EASTERN HIMALAYA

Prakash Chhetri, Anup Chandra and Ghanashyam Sharma

Abstract

This study is an attempt to find the impact of disturbances on tree species richness, population structure and regeneration status in the tropical forest of Sikkim. On the basis of Disturbance indices forest were categorised into Highly Disturbed (HD), Moderately Disturbed (MD) and Least Disturbed (LD). While, number of species was considered as species richness in different disturbance gradient, population structure was determined using density diameter relation. Similarly, regeneration status was seen based on the density of seedling, sapling and adult tree species along the disturbance gradient. Species richness was highest (29) at LD sites and lowest in HD (24) and 25 in MD. Population structure of the forest across the sites were normal with densities of seedling>sapling>adult, but densities in all growth form were higher in LD followed by MD and HD. Seedlings of Shorea robusta, Schima wallichi and Tectona grandis dominated the forest floor, comprising of 85% of all the seedling density. Although most of the species regenerated better in LD sites, species like Schima wallichii, Tectona grandis, Terminalia bellirica and Lagerstroemia parviflora had better seedling densities in MD sites. LD sites showed highest percentage of good (31 %), fair (17 %) and new (20 %) regeneration. Highest percentage of poor regeneration was observed in HD (27) sites followed by MD (23) and LD (11) while 29 % of the species were not regenerating and MD sites followed by HD (27) and LD (20). This study concludes that the anthropogenic disturbance is detrimental for species richness, population structure and regeneration of tree species yet moderate disturbances may be beneficial for regeneration of few selected species.