## 3 Results
### Influence of LUCC on the Change of Grassland NPP in Inner Mongolia  
Human activities obviously affect LUCC, which in turn influences the growth of vegetation and its NPP. The research by [PERSON] et al. (2018) showed that the global urbanization-induced decrease in global NPP offset 30% of the climate-driven increase over the same period. In this study, we applied the LUCC of 2000, 2010, and 2020 as a mask to extract the grassland NPP in the corresponding range, to analyze the influence of LUCC on the change of grassland NPP. As Figure 10 shows, the grassland NPP maintained an increasing trend in 2000, 2010, and 2020. The average NPP increased from 250.28 g C/m\({}^{2}\) in 2000 to 257.13 g C/m\({}^{2}\) in 2010, and then to 303.25 g C/m\({}^{2}\) in 2020. The total NPP in Inner Mongolia was 134.40, 141.75,  
Figure 9: Spatial distribution of the slope of grassland NPP obtained by the Theil–Sen method (**a,c,e**) (unit: g C/(m\({}^{2}\cdot\)yr)) and its significance by the MK test (**b,d,f**) (\(\alpha=0.05\)) in Inner Mongolia during the different periods. and 164.28 Tg C in 2000, 2010, and 2020, respectively. In terms of the spatial distribution, the area of medium-level NPP (200-400 g C/m\({}^{2}\)) increased from 2000 to 2020, accounting for 32.62%, 36.59%, and 37.47% in 2000, 2010, and 2020, respectively, which was obvious in north Xilingol, Chifeng, and Tongliao. This indicates that the area of grassland with medium to high quality has increased. From the perspective of the different LUCC changes (Table 6), the different types of LUCC conversion had various effects on the grassland NPP. From 2000 to 2010, 24016.81 km\({}^{2}\) of grassland was transferred to other land-use types, causing a loss of 8.29 Tg C in NPP, while 38,304.13 km\({}^{2}\) changed to grassland, bringing an addition of about 9.65 Tg C in NPP. Although in terms of area, the grassland area increased, but the average NPP of the lost grassland (345.23 g C/m\({}^{2}\)) was higher than that of the added grassland (251.91 g C/m\({}^{2}\)). Taking the conversion between bare land and grassland as an example, from 2000 to 2010, grassland changing from bare land accounted for 15,733.63 km\({}^{2}\), bringing 0.74 Tg C in NPP. Although grassland changing to bare land only accounted for 3288.31 km\({}^{2}\), it caused a loss of 0.35 Tg C in NPP. This shows that although the lost grassland was a lesser area, the quality was good, while the added grassland was a greater area, but the quality was poor. From 2010 to 2020, the area of lost grassland increased (48,920.19 km\({}^{2}\) and 14.96 Tg C NPP) and was more than the area of added grassland (39,361.56 km\({}^{2}\) and 10.73 Tg C NPP). As a result of human reclamation, a large area of grassland, i.e., 26,495.25 km\({}^{2}\) (54.16% of the total lost area), was converted into cultivated land, which led to a loss of 8.36 Tg C in NPP. Figure 10: Spatial distribution map for NPP in the Inner Mongolia grassland based on LUCC in (**a**) 2000, (**b**) 2010, and (**c**) 2020. (**d**) The change of grassland NPP. During this period, the average NPP of grassland changed to bare land was 100.72 g C/m\({}^{2}\), and the average NPP of grassland changed from bare land was 82.48 g C/m\({}^{2}\). In general, the quality difference between the new and lost grassland still existed, but there was some improvement compared with the period of 2000-2010. However, the total area of grassland decreased during 2010-2020. Overall, from 2000 to 2020, 59,141.81 km\({}^{2}\) of grassland was changed into other land-use types, resulting in a loss of 17.63 Tg C in NPP. As a comparison, 63870.50 km\({}^{2}\) of other land-use type changed into grassland, but this led to an addition of only 16.38 Tg C in NPP. In total, 26130.44 km\({}^{2}\) grassland (44.18% of the total lost area) of high quality changed into cultivated land, for which the average NPP was 283.38 g C/m\({}^{2}\). A further 33,086.56 km\({}^{2}\) of bare land changed into grassland (51.80% of the total added area), with a poor average NPP of 69.97 g C/m\({}^{2}\).