Patterns of plant communities along vertical gradient in Dhauladhar Mountains in Lesser Himalayas in North-Western India

Abstract

Mountains are definitely the most rugged, yet frail resources and biodiversity-rich regions of the world. Environmental variables directly affect species composition, growth patterns, and the ecosystem resulting in a drastic change in the vegetation composition along ascending elevations. The present study investigated vegetation composition, nestedness, and turnover in plant communities along a vertical gradient (2000 to 4000 m) in Dhauladhar Mountains, Lesser Himalayas, India. We determined how α-diversity pattern and nestedness-related processes or turnover (β-diversity) causes dissimilarity in plant communities' composition along the vertical gradient. Overall, 21 permanent plots (20 × 20 m²) at every 100 m interval from 2000 to 4000 m were established. A sampling of shrubs and herbaceous species was done by marking sub-plots of 5 × 5 m² and 1 × 1 m², respectively, within permanent plots. We observed an inverted hump-shaped pattern for evenness index (E), a unimodal hump-shaped pattern for Shannon index (H'), Margalef's richness index, and β-Whittaker (β_w) diversity, and mild-hump-shaped pattern for Simpson index (λ) across the elevational gradient. Turnover (β_sim) and the nestedness-resultant component of β-diversity (β_sne) significantly differed across the elevational gradient. The observed β-diversity patterns revealed that the species replacement rate was less in the mid-altitude communities as compared to lower and higher altitude communities. It was largely attributed to the ecotonic nature of mid-altitudes, which benefited mid-elevational communities rather than low or high altitude communities. Besides lower altitudes, the increased human interference has led to disturbance and subsequent homogenization of flora across the mid-altitudes. With respect to this, the present study signifies the need for preserving the mid-altitudinal communities, without undermining the importance of conserving the low and high altitude communities.

Keywords: Mid-altitudes; Nestedness; Richness; Species replacement rate; Turnover rate; β-Diversity.