Potential distribution of Apocynum based on MaxEnt optimization model

The Apocynum species, a valuable economic crop known for its robust resistance and high tolerance, was analyzed in this study．The maximum entropy model (MaxEnt) optimized by ENM Tools was used to simulate three Apocynum species: Apocynum pictum (Sohnenk.) Baill, Apocynum hendersonii (Hook．f.) Woodson and Apocynum venetum L. Simulation was conducted under current climate conditions and two future time periods (2041-2050 and 2061-2070) by RCP4.5 discharge model．Main environmental factors affecting distribution of each species were analyzed, impact of climate change on their distribution was examined．Geographical distribution of these species was found influenced by different dominant environmental factors．The dominant environmental factors affecting distribution of A. pictum were: wettest quarterly precipitation, seasonal variation in precipitation, and altitude．The main environmental factors affecting distribution of A. hendersonii included monthly mean diurnal temperature difference, maximum temperature in the hottest month, wettest quarterly precipitation, slope orientation, and surface (0-30 cm) sand content．Altitude, annual temperature range, wettest quarterly precipitation, and seasonal variation in precipitation were the key factors influencing A. venetum distribution．The habitats of these species showed clear differences in distribution．Some ecological niche was found to overlap between A. pictum and A. hendersonii, while A. venetum had less ecological niche overlap with the other 2 species．Distribution centers of A. pictum and A. hendersonii were predicted for the future to shift to higher latitudes and altitudes, with A. venetum distribution center shifting northwards．These data provide theoretical guidance for cultivation and conservation of Apocynum, and serve as reference to understand effects of climate change on species distribution．