Predicting suitable habitat of an invasive weed Parthenium hysterophorus under future climate scenarios in Chitwan Annapurna Landscape, Nepal

Chitwan-Annapurna Landscape (CHAL) in central Nepal is known for its rich biodiversity and the landscape is expected to provide corridors for species range shift in response to climate change. Environmental assessments have identified biological invasions and other anthropogenic activities as major threats to the biodiversity in the CHAL. One of the rapidly spreading Invasive Alien Plant species (IAPs) in the CHAL is Parthenium hysterophorus L., a neotropical invasive weed of global significance. This study aimed to investigate the current and future projected suitable habitat of P. hysterophorus in the CHAL using MaxEnt modelling in three “Representative Concentration Pathways” (RCPs 2.6, 4.5 and 8.5) corresponding to different greenhouse gases emission trajectories for the year 2050 and 2070. A total of 288 species occurrence points, six bioclimatic variables - mean diurnal range, isothermality, annual precipitation, precipitation of driest month, precipitation seasonality, precipitation of driest quarter and two topographic variables (aspect and slope) were selected for MaxEnt modelling. Potential range shift in terms of increase or decline in the suitable habitat areas under the projected scenarios were calculated. Slope and annual precipitation were the most important variables that explained the current distribution of P. hysterophorus. Twenty percent of the total area of CHAL was predicted to be suitable habitat for the growth of P. hysterophorus in the current climatic condition. Highest gain in the suitable habitat of this noxious weed was found under RCP 4.5 scenario in 2050 and 2070, whereas there will be a loss in the suitable habitat under RCP 8.5 scenario in 2050 and 2070. Out of four physiographic regions present in CHAL, three regions - Siwalik, Middle Mountain and High Mountain have suitable habitat for P. hysterophorus under current climatic condition. The mountainous region is likely to be affected more than the Siwalik region by further spread of P. hysterophorus in the future under low (RCP 2.6) to medium (RCP 4.5) emission scenarios. The suitable habitat for this weed is likely to increase in the protected areas of mountain regions (Langtang National Park, Annapurna Conservation Area and Manaslu Conservation Area) in the future. The results have revealed a risk of spreading P. hysterophorus from present localities to non-invaded areas in the current and future climatic condition. Such risk needs to be considered by decision makers and resource managers while planning for effective management of this weed to reduce its ecological and economic impacts in the CHAL.