Grasslands are more vulnerable to plant invasions than forests in south-central Nepal

Understanding the patterns of plant invasions across vegetation types and identifying the underlying drivers for such patterns is essential to prioritize sites for the effective management of invasive species. We sampled three forest types (Shorea robusta, Dalbergia sissoo, and Tropical deciduous riverine forest) and two grasslands in south-central Nepal to evaluate the richness of naturalized and invasive alien plant species (IAPS). Species richness of naturalized species and the IAPS among vegetation types within each physiographic region was compared using analysis of variance and t-test, and the ordination was used to analyze species-environment relations. Of the total 327 species of vascular plants recorded, 14% were naturalized, and over a third of the naturalized species were invasive. Grasslands had the highest richness of naturalized species and the IAPS. In contrast, S. robusta forest had the lowest naturalized and IAPS richness. Naturalized species richness increased with native species richness. Ordination revealed that a high number of IAPS were associated with areas exposed to frequent fire and livestock grazing and close to human settlements. The results suggest that the grasslands closer to the human settlements and exposed to frequent disturbance are vulnerable to the establishment of IAPS. Early detection and control of IAPS in such frequently disturbed grasslands could prevent their spread into the surrounding landscapes.