By comparing the predicted suitable areas in the 1950s and 1990s, it can be seen that there are differences in the response of Leonurus japonicus to climate change, and that the trends are different (Figure 4). Under the ssp585 scenario, the highly suitable area of L. japonicus changed the most. By the 2050s, the highly suitable area decreased by 98,904 km2, 72.93% lower than the current area. By the 2090s, the area is reduced by 129,243 km2, a decrease of 95.30%. Under the ssp126 scenario, the highly suitable area of L. japonicus in the 2090s decreased the least, being 53,296 km2 less than the current area for a decrease of 39.30%. Under the ssp245 scenario, the highly suitable area decreased by 93,767 km2 in the 2050s, a decrease of 69.14%. The area of the 2090s decreased by 29,136 km2 compared with the 2050s, a decrease of 69.62%. Under the three climate scenarios, the suitable area of L. japonicus showed a decreasing trend, and it was most sensitive to climate change under the ssp245 and ssp585 scenarios.
In terms of spatial pattern, there were large differences in suitable migration locations of L. japonicus under different climate scenarios, but the overall migration trend was more consistent; the overall trend migrates northward (Figure 5). At present, the centroid of the suitable area of Leonurus japonicus is in Lixian County, Changde City, Hunan Province (111.43°E, 29.90°N). Under the climate scenario ssp245 in the 2090s, the center of mass of the suitable area ofLeonurus heterophyllus would be the farthest north. At this time, the center of mass of the suitable area of Leonurus heterophylluswould be located in Xixia County, Nanyang City, Henan Province (111.55 ° E, 33.43 °N); the migration distance would be 391,314 m. Under the climate scenario ssp585-2090s, the movement distance of the centroid of the suitable area of L. japonicus to the northwest is 413,003 m, moving to Dazhu County, Dazhou City, Sichuan Province (107.23 °E, 30.68 °N). Under future climate change scenarios, global warming and humidification will cause the mass center of the suitable growing area of L. japonicus in China to move northward as a whole, and the migration location would trend toward further northwestward expansion.
3.4. Evaluation of environmental factors
The results of the environmental factor evaluation are shown in Table 4. The factors contributing more than 5% to the potential geographical distribution of L. japonicus (Zhan et al., 2022) were the lowest temperature in the coldest month (12.2%), the precipitation in the wettest month (53.8%), the precipitation in the driest month (5.7%) and altitude (20.9%). The total contribution rate of these four environmental factors was as high as 92.6%. The factors with more than 5% of the importance value were the highest temperature in the hottest month (10.6%), the lowest temperature in the coldest month (19.4%), the precipitation in the wettest month (40.3%), the precipitation in the driest month (5.8%), and the altitude (11%). The importance values of these five environmental factors were as high as 87.1%. Considering these five environmental factors as the main environmental factors, precipitation was the dominant factor.
Table 4 Contribution rate and importance of environmental variables