Species Distribution and Ecological Niche Modelling of Alnus Species in Nepal

Abstract

lnus (Alder) is important taxa in agroforestry system because of its ability to fix atmospheric nitrogen. Himalayan alder species such as A. nepalensis and A. nitida are proven to be very useful in traditional as well as contemporary agroforestry practice. This implies to the importance of studying biogeographical distribution of these species to identify the climatical suitable zone. The climatic suitable zone of two species of genus Alnus were modelled using a subset of least correlated bioclimatic variables for current condition (19502000), topographic variables (DEM derived) and Landuse Landcover (LULC) data.

MaxEnt method was used to predict the suitability of Alnus species based on 79 randomly distributed points (67 of A. nepalensis and 12 of A. nitida). Four models were produced for each species in a stepwise combination of variables. The best model was choosen against random model based on AUC value of Maxent using ANOVA and t-test. The model selected for further analysis comprises mean AUC value of 0.889 for A. nepalensis and 0.946 for A. nitida. The environmental variables that best explained the current distribution of the species were identified and used to project the climatically suitable niche into the future, and identify the suitable areas for mixed agroforestry. The most favourable conditions for A. nepalensis were located in Central Nepal in the moist North-West facing slope and degraded hilly region above Siwalik range from East to West; whereas, that of A. nitida was located in drier SouthEast

facing Western Himalaya along river valley of Nepal. The model reveled that the Dhaulagiri Range and Annapurna range separates habitat of two Alnus species in Nepal. The rising mountain slopes in the northern region even acts as barriers for A. nepalensis distribution. Presence of rough terrain of high Himalaya fragmented the habitat of A. nitida. The major contribution factor for distribution in Nepal was found to be precipitation of warmest quarter and precipitation of drier quarter for A. nepalensis and A. nitida respectively. The model revealed that climatically suitable area occupied for A. nepalensis is ca. 47610 km 2 and A. nitida ca. 14690 km 2

in current scenario. While in the future projection of SRESA1B scenario for 2050, A. nepalensis was found to decrease its suitability area by ca. 16720

km 2 whereas that of A. nitida decreases by ca. 3405 km 2 . Prediction for SRES-A1B scenario 2050 shows significant loss in area of Alnus species (15.74% for A. nepalensis and 5.38% for A. nitida) as compared to the suitable area gained ( 7.32% for A. nepalensis and 0.67% for A. nitida). The unchanged stable areas in Hilly region are probable sites for the introducing these species in the agroforestry system.