Impact of climate change on potential distribution and altitudinal shift of critically endangered Amentotaxus assamica DK Ferguson in Arunachal Pradesh Himalaya, India

Climate change has significantly affected the potential distribution and altitudinal shift of several plant species. Amentotaxus assamicus being one of the critically endangered gymnosperms under the family Taxaceac is restricted only to a few pockets of Arunachal Pradesh with low population size. The current study aims to analyze the current distribution of A. assamica in the state using key environmental parameters and to predict the potential suitable habitat in accordance with two IPCC representative concentration pathway (RCP) scenarios. The future potential distribution was projected for two possible climate scenarios (RCP 4.5 and RCP 8.5) given by three various global climate models (GCMs), viz., BC_CSM 1.1 (BC), CCSM4 (CC), and CNRM-CM5 (CN). A total of 36 independent localities of A. assamica were used to model the current species distribution along with 23 environmental variables, including bioclimatic parameters, elevation, global land cover, and soil data. To run the future simulations, IPCC AR5 scenarios were used for 19 bioclimatic variables. Maxent modeling was used for the current distribution of A. assamica in Arunachal Pradesh, India, through 10 duplicate runs which showed the test AUC average of 0.905 as well as a standard deviation of 0.057. Soil available nitrogen at 15 cm depth was found to contribute the maximum in the model accounting for 38.2% followed by soil nitrogen at 5 cm depth (21.8%). Bio 4, Bio 6, Bio 7, and Bio 19 were the key variables that contributed to varying extent in all the three GCMs consisting of two scenarios each. Under the high suitability zone, the optimistic scenario (RCP 4.5; 3618.25 km2) represented the maximum area followed by RCP 8.5 (3269.89 km2) whereas the lowest in the current distribution model revealed as 2909.64 km2. Furthermore, the high suitability distribution range in terms of altitudinal regime shifted from 270 msl of lowest elevation in the current distribution to the 966 msl in the RCP 4.5 scenario and 894 msl in the RCP 8.5 scenario. The altitudinal shift of the distribution found in the futuristic model is significant, and the species' lower range of altitudinal distribution has clearly shifted upward. The findings of this study would be useful in determining quantified future climate space for the species and allow the conservation managers to formulate appropriate conservation strategies.