Diversity of naturalized plant species in a Ramsar-listed wetland complex of a mountain valley in the Nepal Himalaya

Biological invasion is one of the leading causes of global biodiversity loss and the degradation of ecosystem services. Wetlands situated within human-dominated landscapes are particularly vulnerable to these invasions. However, extent of plant invasions in many wetlands remains insufficiently known for guiding effective management. This study aimed to analyze the status of plant invasions in the Lake Cluster of the Pokhara Valley (LCPV), a Ramsar site encompassing nine wetlands in the rapidly urbanizing region of central Nepal. A total of 89 plots (20 m×5 m) along the lakeshore were surveyed to record the richness and coverage of both native and naturalized plant species. Water samples were also collected from each plot to measure nitrogen and phosphorus levels. Data were analyzed using analysis of variance, generalized linear models, multiple regression, and canonical correspondence analysis. The results revealed significant variation in native and naturalized species richness and composition across the wetlands. Naturalized species richness was positively correlated with native species richness. Species richness was the highest in the smallest wetlands site (i.e., Kamalpokhari) and the species composition of the largest wetland site with the highest tourist visitation (i.e., Phewa lake) was distinctly different from the rest of the other wetlands. Species composition similarity increased when only the naturalized species were accounted, relative to the scenario when only native species were considered, suggesting increased homogenization due to plant invasions. No significant effects of nitrogen or phosphorus levels on species richness or coverage were found. Understanding these local drivers that affect naturalized plant diversity in the LCPV can inform management strategies to protect these wetlands from further invasion by alien species.