Impact of invasive plants on vegetation in protected areas of Nepal

Protected areas are expected to harbour fewer invasive plants due to the absence of anthropogenic disturbance and greater resistance of natural vegetation to invasion. Our study aimed to quantify the impacts of selected invasive plants on native plant species richness, diversity, and composition in five protected areas of Nepal spread across ~ 3403 km² at the Himalayan foothill. Lantana camara, Mikania micrantha, and Parthenium hysterophorus were selected as target species based on their abundance in the study area. For each species, 30 pairs of invaded and uninvaded plots of 10 × 10 m were sampled to record the presence and covers of all vascular plants. The impacts of invaders on species diversity were analyzed using linear mixed-effect models, those on plant community composition by direct gradient ordination. The analysis of merged data, including all studied invaders, showed that the invasions reduced native species richness and diversity, which decreased to less than half of the values recorded in uninvaded plots. Similarly, each of the three species had a significant negative impact on native species richness and diversity when tested separately, with M. micrantha having the greatest impact, followed by P. hysterophorus and L. camara. In addition, the invasion by L. camara explained the greatest percentage of variation in the species composition of the invasive species studied. The results support the invasion meltdown theory, as the invasion promoted the presence of other alien species in the invaded plots.