3.5 Distribution and change of land use pattern in climate-stable areas of T. chinense in China
Kappa coefficient was used to verify the simulation accuracy between the simulation results in 2015 and the actual land use data in 2015. The results showed that the overall accuracy of the simulation results of land use change in 2015 was 0.992 and Kappa=0.990, indicating that the PLUS model was reliable and could predict future land use distribution. The contribution degree of driving factors of each land use type change was shown in Table S7. The largest contribution of driving factor of grassland areas change was distance from water, followed by annual precipitation (Figure. 7B).
Under different climate scenarios, the total area of climate-stable areas of T. chinense in China is about 480.01 * 104 km2 (Figure 7A). According to the expansion and contraction trends of land use in 2010 and 2015, the distribution pattern of land use in 2050, 2070 and 2090 within the climate-stable areas is predicted (Figure S4). Among them, the cultivated land, grassland, and unused land in the climate-stable areas show a downward trend. And by 2090, they will decrease by 1.63%, 13.84%, and 10.67%, respectively, compared with 2015 (Figure 7C). In the future, the land use types transferred to grassland types mainly are forest, unused land, and construction land. From 2050 to 2070, the areas will transfer from forest, unused land, and construction land to grassland is about 1.83 * 104 km2, 0.90 * 104 km2, and 0.70 * 104 km2. With the increase of the years, the transferred areas gradually increase, and it is estimated that the transferred areas from 2070 to 2090 are about 3.00 * 104 km2, 0.97 * 104 km2, and 1.08 * 104 km2. In the future, grassland will mainly transfer to forest and construction land, and the transferred areas will increase from 4.65 * 104 km2 and 1.98 * 104 km2 in 2050 and 2070 to 5.80 * 104 km2 and 2.26 * 104 km2 in 2070 to 2090 (Figure 7C and Table S8). In the future, the area of forest, waters, and construction land in this region will show an increasing trend, especially the construction land. By 2090, the area of forest and water will increase by 5.51% and 1.49%, respectively. Construction land will increase to 25.71 * 104 km2, expanded by about 46.94%.