Invasive Weeds Reduce Plant Diversity and Alter Species Composition in Rangelands of Tropical Protected Areas in Nepal

Invasive alien species pose significant threats to biodiversity and ecosystem functioning in protected areas (PAs) worldwide. This study examines ecological impacts of invasive weeds Lantana camara and Mesosphaerum suaveolens on plant species diversity, community composition and soil chemical properties in Parsa and Shuklaphanta National Parks (NPs), Nepal. In total, we sampled 180 pairs of 5 m × 5 m plots, comprising 45 pairs (3 sites × 15 pairs) for each invasive species in each NP. Across all sampling sites, these weeds consistently reduced species diversity (Shannon, Simpson indices), despite the species- and site-specific variations in species richness and soil characteristics. Non-metric multidimensional scaling and Canonical correspondence analysis revealed substantial modifications in plant species composition, along with shifts in indicator species and an increase in the relative cover of established alien plants in invaded plots. While the effects of invasions on soil properties were inconsistent, L. camara significantly increased soil organic carbon and total nitrogen in Parsa, whereas M. suaveolens had no measurable impact on soil parameters except soil pH in either PA. These results suggest that species diversity indices and changes in species composition serve as reliable ecological indicators for assessing impacts of invasive weeds and monitoring ecological restorations. The decline in species diversity and alterations in plant community composition can have cascading effects on ecosystem processes and livelihoods of local communities. Given the increasing threats of plant invasions in Nepal’s PAs, urgent and effective management interventions are needed to prevent further spread, mitigate ecological and socio-economic impacts, and restore invaded habitats.