Distribution modelling of traded species of Swertia L. and population ecology of S. Multicaulis in Nepal

Abstract

The genus Swertia has a long history of usage in Indian, Tibetan, and Nepalese traditional medicine. The species of the genus have been widely used as a natural remedy for a variety of ailments. Because of high ethnomedicinal and pharmacological values, Swertia has become a major export of medicinal plants from Nepal and ranks as the second most traded genus in the country. The growing demand for medicinal plants has led to unsustainable harvesting, making conservation efforts necessary. Additionally, climate change has also affected the accessibility and productivity of medicinal plants. To address this, firstly, distribution models of traded species of Swertia were developed based on maximum entropy and secondly, an ecological study of less studied S. multicaulis was conducted. The study identifies the potentially suitable areas of seven commercially traded species of Swertia under the current climate conditions and predicts a significant decrease in suitable areas for all of the species by 2050 and 2070 AD in both representative concentration pathways (RCP 6 and RCP 8.5), with the exception of S. racemosa. The ecological study was conducted at four different sites around the Gosainkunda area in Lamtang National Park. The study involved a total of 40 plots of 3m 2 and 200 sub-plots, each measuring 1m 2 , that recorded the presence of S. multicaulis in open alpine meadows on north-east facing slopes at different elevations. The overall density was found to be 11.33 plants/m 2 . The densities of young and adult reproductive plants decreased significantly with increasing elevation. In the lower elevation sites, the proportion of young plants was higher, indicating better regeneration there. Despite the similar vegetative and reproductive traits among all populations studied, the higher elevation population near Suryakunda, which featured rocky terrain, had a higher below-ground biomass allocation. The study also revealed the negative effect of litter cover on the total plant density of S. multicaulis. But the density positively correlated with greater distance from the nearest trail. The findings of the ecological study of S. multicaulis as well as the habitat suitability map for seven traded species of Swertia created by the distribution models can be utilized as a reference for developing conservation policies for such species and also prioritizing those areas as potential areas for cultivation or harvesting purposes. For species like S. multicaulis, with very limited climatic suitability in a specific region, our study recommends facilitated assisted migration to predicted suitable areas as the optimal solution to ensure their future.