Anthropogenic disturbance impact on forest composition and dominance-diversity: A case of an ecosensitive region of Garhwal Himalaya, India

A total of twenty four forest types were selected along altitudinal and disturbance gradients on various aspects to analyse the composition, diversity and distribution of tree species in an ecosensitive region of Garhwal Himalaya. A significant impact of anthropogenic/human induced disturbance was recorded on the existing community parameters, consequently the density, Total Basal Cover (TBC) and species diversity values were decreased with increseasing disturbance intensity. The overall density was recorded in the range from 411 trees ha⁻¹ to 840 trees ha⁻¹, whereas the TBC values existed between 21.72 m² ha⁻¹ to 95.41 m² ha⁻¹. The canopy structure of the forest (mostly in moderate disturbance condition) has significantly (P ≤0.05, r = 0.439), whereas the light attenuation significantly but negatively (P≥0.05, r = −0.445) impacted the growth of ground herbaceous vegetation. The Cedrus deodara (Roxb. ex D.Don) G.Don (between 1600 and 3000 m asl), Lyonia ovalifolia (Wall.) Drude (1832–3000 m asl) and Rhododendron arboreum Sm. (1832–3000 m asl) species have shown a very wide ecological amplitude for their range distribution in study area. The Canonical Correspondence Analysis has categorized the canopy forming tree species into different patches by identifying the prominent disturbance indices/parameters according to their niche resource requirement in the study area. The obtained dominance-diversity curves reflected mostly the geometric type of model for trees, however lognormal to log type of models for shrubs and herbaceous vegetation. Overall, this study reviews enough evidences of species susceptibility towards fragmentation of habitats because of anthropogenic disturbance. Moreover, the current species range distribution records will help to develop baseline datasets for existing tree species to access in future for their range shift from the conventional habitats due to climate change and notify them as climate sensitive species in Himalaya.