Diversity of naturalized plant species across different land use types in Kailali district, western Nepal

Abstract

With the increasing movement of organisms directly and indirectly by human activities across natural biogeographic barriers, the number of naturalized plant species has been increasing both in disturbed and human-modified ecosystems. Due to variation in propagule pressure of naturalized plant species, available resources, disturbance regimes and species interactions, diversity of naturalized species may vary across vegetation and land use types. Naturalized plants species richness measured in different vegetation and land use types in Kailali district by using Modified-Whittaker nested vegetation sampling method (50 m × 20 m) and five plots were sampled in each of the seven land use types so, total number of sampling plots were 35. We recorded 792 species including 22 pteridophytes, 1 gymnosperm and 769 angiosperms; among them 670 were native species, 87 naturalized species and remaining 35 species were cryptogenic. Species richness of native, naturalized and invasive species significantly (p<0.05) varied across land use types. Naturalized species richness was the highest in roadside grazing land (17.2±1.35), followed by agriculture land (11.4±2.11) and it was the lowest in Shorea-Terminalia forest (3.6±1.43). Among invasive species Ageratum houstonianum was the most frequent (41%), followed by Senna tora (33%). However, Senna tora had the highest cover (64%) followed by Ageratum houstonianum (30%). The naturalized species richness showed significant relation (p≤0.05) with grazing, native species richness, distance from river, tree canopy cover, soil pH, distance from settlement area and distance from road. Also, invasive species richness was significantly correlated with naturalized non-invasive species richness, grazing, tree canopy cover, soil pH, native species richness. Present study revealed the naturalized species were more colonized in human-modified and disturbed land use types that provide propagules for further spread to other vegetation and land use types in the region so, land use modification and disturbance factors as major governing factors for the naturalized plant species diversity. Therefore, the more modified and disturbed land use types should be regularly monitored for early detection and eradication as a part of management strategy for naturalized plant species.