Vegetation Structure Along an Elevation Gradient at the Treeline Ecotone of Eastern Himalayan Forests in Sikkim

Abstract

This chapter presents an extensive vegetation analysis for Yuksam-Dzongri transect in Sikkim (in the eastern Himalaya). The investigation was conducted along an elevation gradient between 1700 m and 4000 m at 100 m elevation steps and considered its physiognomy life form, species-area relationships and species compositional changes. The plant species assemblages in the transect was represented by 267 species belonging to 174 genera and 81 families. The familial composition showed the predominance of Ericaceae, Fagaceae, and Lauraceae in tree layer; Ericaceae, Rosaceae, Berberidaceae, and Rubiaceae in shrub layer, and Compositae, Polygonaceae, Rosaceae, and Primulaceae in the herb layer. The species richness (tree, shrub, and herb) and total basal area (TBA) of trees declined monotonically along the elevation gradient with peaks at 1700–1900 m. The tree density in present studied transect was significantly higher than in its western Himalayan counter parts of Indian Himalayan region. The presence of 77 tree species in the high forested zone highlights the high tree species richness of the eastern Himalaya to which the contribution of Rhododendron was particularly high. Sparse canopy layer and dense undercanopy tree layer were the characteristic features of the forests. Further, inclusion of biotic interactions and disturbance may improve ecological understanding of these patterns of plant species richness across the Indian Himalayan region.