Current and future potential distributions
Potential distributions of A. annua were projected by ensemble models under current and future climate scenarios. Based on the value of presence probability, the distribution could be categorized into three classes respectively. The area with value ranged from 0-0.2 was low suitable area, the area with value ranged from 0.2-0.5 was medium suitable area, and the area with value ranged from 0.5-1 was high suitable area.
According to the projection of ensemble model under current climate scenario, the high suitable areas for A. annua were located in Eastern Asia, Western Europe, Central Europe, eastern part of Northern Europe, western part of Eastern Europe, south and east edge of Australia, eastern coast of North America, northwest part of Great Plains in U.S., southeast coast and Andes Mountains in South America (Fig. 3). The medium suitable areas were located in west of China, Eastern Europe, central and east of U.S. and southeast of South America.
Due to different climate scenarios, the future potential distributions ofA. annua differed. The outputs showed that, the pixel numbers for high suitable habitats increased with time under each SSP (Fig. 4). The largest growth occurred under SSP 585, its percentage raised up to 7.18% (average of 2080-2100) from 6.34% (average of 2021-2040).
Although, compared with the current one, the pixel numbers declined sharply under future climate scenarios. The percentages ranged from 15.55% (average of 2081-2100 under SSP 585) to 25.87% (average of 2021-2040 under SSP 126). After analyzing the projections of ensemble models under different climate scenarios and periods, we figured out the gain and loss of high suitable habitats in the future. According to the result, the shift patterns of different periods under SSP 126 was demonstrated below (Fig. 5). Almost all the high suitable habitats which located in North America degraded. The high suitable habitats in Europe presented a trend moving toward east, they were loss in Atlantic coast and gain in East Europe. In Asia, the habitat shift area mainly located around China, most of degraded areas were in northwest China and north of China, major parts of upgraded area spotted along the border of southwest China and south China. Under the other three SSPs, the gain and loss acted a same pattern as the one under SSP 126, which could be checked in supplementary materials (see Appendix S1).