Diversity and Distribution of Invasive Alien Plant Species Along Road Network in Central Nepal

Abstract

Invasive alien plant species are spreading rapidly in Nepal and can have irreversible environmental and economic problem if not managed in time. For the proper management of IAPS detail information regarding their diversity and distribution is needed. In this study a detail survey of IAPS distribution was carried out during June- July in 2013 along road networks in Central Nepal. The study also dealt with the variation in species richness pattern across land use types and along elevation gradient. IAPS distribution was assessed through systematic location of sample plots at an interval of 10km in plain areas and 5km in hilly areas. At every specified distance, a 10 × 10 m x

2 plot was defined along the sides of the road. At each plot, IAPS encountered within the plot, their phenophases, presence of biocontrol agents and three most dominant IAPS in terms of cover were recorded. The cover was estimated visually and the frequency of individual IAPS was calculated. The geographical distribution map of each IAPS and overall species richness distribution pattern map was prepared using Arc GIS. A total of 340 plots were sampled covering 2075km of road network. Among the 18 species of invasive alien plants recorded from roadside vegetation, Bidens pilosa had the highest frequency whereas Eichhornia crassipes had the lowest. And Ageratina adenophora was the first dominant species in 30% of the sample plots. IAPS richness showed unimodal pattern of distribution along the elevation gradient. There was significant difference in species richness across land use types. Grazing and fallow land was more vulnerable to invasion, as reflected by the highest species richness in comparison to other land use types (Agricultural land>Shrubland>Forest>Wetland). A negative linear relationship was obtained between frequency (%) and year of record of the IAPS. There was no significant relationship between elevational limit and minimum residence time of IAPS. Most of the IAPS were concentrated to the tropical and sub-tropical region. Middle mountains had greater IAPS richness in comparison to other physiographic regions.This study concludes that IAPS have been spreading rapidly along road networks in Central Nepal. The road networks are acting as dispersal corridors and source areas for plant invasion. Therefore, comprehensive study of IAPS distribution and their impacts has to be carried out at national level which may be useful to develop management strategies for controlling biological invasion. Keywords: Biological invasion, Invasive alien plant species, Species richness, Elevation gradient, Disturbance, Road network, Frequency, Residence time, Distribution maps.