Anthropogenic Disturbances and Invasion of Mikania micrantha Threaten Rauvolfia serpentina Populations in Nepal.

Rauvolfia serpentina (L.) Benth. ex Kurz (family: Apocynaceae), a threatened medicinal plant in Tropical Asia, faces rapid depletion due to unsustainable harvesting, human-mediated habitat alteration, and invasion of alien species. Lack of knowledge regarding its population status, ecology, and performance hinders effective species-specific conservation management plans. Therefore, we studied the population density and structure of R. serpentina and assessed the variation in its life history traits (e.g., adult plant height, adult stem diameter, adult canopy diameter, number of branches, fruit circumference, dry fruit mass, and reproductive output), and regeneration status among populations at four sites differentially disturbed from human pressure and invasion of Mikania micrantha Kunth (family: Asteraceae)-highly disturbed, moderately disturbed, undisturbed, and previously disturbed-in the Jalthal forest in eastern Nepal. We conducted seed germination tests in a polyhouse to determine the seed germination potential and seedling growth performance on four different canopy types based on presence or absence of Mikania micrantha e.g., open without-mikania, semi-close without-mikania, close with-mikania and close without-mikania. The highest density (2.53 ± 0.22 individuals 25 m2) was recorded in the undisturbed site. R. serpentina density greatly reduced with increasing disturbance. Compared to disturbed sites, undisturbed site showed high seedling recruitment and had adults with better growth performance and reproductive output. Habitat destruction and alteration, invasion of alien species, over-harvesting, and poor seed viability are the probable reasons behind the reduced regeneration and low population density of R. serpentina in Jalthal forest. The results showed that R. serpentina was very sensitive to anthropogenic disturbances and the invasion of alien species, which contributed to the variation in density, life-history traits, and regeneration potential in differentially disturbed sites. Furthermore, this species struggles to sustain and compete with others in disturbed habitats due to its low seed germination.