Facilitative effects of a Dwarf Shrub in an Alpine Rangeland

Abstract

Cushion-like plants play a significant role of enhancing and maintaining biodiversity in alpine areas; facilitating germination, growth and survival of plants growing within their canopy. However, literature is unclear on whether dwarf shrubs can play the same role in alpine habitats. This study examined the distribution of plant species and their association with a dominant dwarf shrub Caragana versicolor in a high altitude rangeland of the Indian Trans-Himalaya. Community data was collected in a paired manner from individual shrubs and equal areas outside. The community within Caragana had 27% greater species richness than the outside. Forbs and grasses, which are important forage, had 30% greater richness and 95% greater abundance within the Caragana canopy, while species with prostrate growth forms were found in greater abundance outside. The narrow edge of the canopy harboured richness and abundance disproportionate to its area – greater richness and abundance than the rest of the canopy, and similar richness to outside plots the size of the whole plant. With an increase in altitude from 4500 to 4900 m, the central portion of the canopy made greater contribution to richness and abundance at high altitude as compared to the low altitude site, consistent with the stress gradient hypothesis. This study shows that facilitative effects of Caragana do significantly modify the plant community of this rangeland, and further study is required to understand the mechanisms underlying this, and the role of herbivory in this interaction.