Expansion of a native species and its impacts on alpine ecosystems, Indian Himalaya

In recent years, a number of studies have reported invasion by alien species, however, global studies on invasion or expansion of native species are still limited, and such studies are completely lacking from the Himalayan region. The study aims to find the direction of correlation between the expansion of a native species (Polygonum polystachyum Wall. ex Meisn.) and plant species richness in the alpine ecosystem of Indian Himalaya. We have carried out vegetation sampling in selected invaded and un-invaded areas along an elevation gradient (3000–4100 m a. s. l.) over a period of four years. Three different sites i.e., Valley of Flower National Park (VoFNP), Lata-Khark and Hemkund Sahib Trek in Nanda Devi Biosphere Reserve (NDBR) were selected for the study. The range of plant diversity was analysed to be 1.2–2.1 in invaded plots, and 2.4–3.7 in un-invaded plots/sites. Average population density of P. polystachyum varied significantly (p < 0.001) between invaded and un-invaded sites, and ranges from 11.1–67.1 individual / meter2 in invaded sites and 0.0–3.8 ind / m2 in un-invaded sites. The result of mixed effects model revealed significant decrease (p < 0.01) in species richness and increase in density and abundance (p < 0.01) of P. polystachyum in the invaded sites during 2015–2018, which imparts negative impacts on plant diversity, particularly on high value threatened medicinal plants.