# Temporal Changes in Land Use, Vegetation, and Productivity in Southwest China
## 3 Results
### Changes in the Center of Gravity of NDVI and GPP  
From 2000 to 2019, the migration direction of the NDVI center of gravity of different land cover types also showed varying differences. The center of gravity of the NDVI value of cropland moved to the southwest by 0.12\({}^{\circ}\) in the meridian and 0.12\({}^{\circ}\) in latitude. Among them, the center of gravity of cropland moved in the southeast direction, moving 0.037\({}^{\circ}\) in the meridian and 0.12\({}^{\circ}\) in latitude from 2000 to 2005; the center of gravity moved in the west direction, moving 0.16\({}^{\circ}\) in the meridian and 0.01\({}^{\circ}\) in latitude from 2005 to 2019; and the center of gravity of the woodland moved to the northeast, moving 0.03\({}^{\circ}\) in the meridian and 0.06\({}^{\circ}\) in latitude. However, the center of gravity moved to the northwest from 2000 to 2005 and continued to move to the northeast from 2005 to 2019. The center of gravity of the grassland continued to move to the northwest from 2000 to 2019 by 0.06\({}^{\circ}\) in the meridian and 0.16\({}^{\circ}\) in latitude. Since 2000-2006 was the main implementation period of the ecological project, the composition of land cover changed greatly, and the change direction of the NDVI center of forest, cropland, and grassland changed (Figure 5). The study found that the migration direction of the GPP gravity center of the same type of LULC type had been consistent with the gravity center migration direction of its NDVI (Figure 5). During the study period, the center of GPP of cropland moved to the southwest. The GPP center of gravity of cropland moved to the southeast from 2000 to 2005, by 0.03\({}^{\circ}\) in the meridian and 0.12\({}^{\circ}\) in latitude, while the GPP center of gravity of cropland moved to the southwest from 2005 to 2019, and the migration amplitude increased, moving 0.15\({}^{\circ}\) in the meridian, while there was almost no change in latitude. The GPP center of gravity of the forest moved to the northeast. From 2000 to 2005, it first moved to the  
Figure 5: Changes in the center of gravity of NDVI and GPP. (Note: (**a**–**c**): Changes in the NDVI center of gravity of cropland, forest and grassland from 2000 to 2019; (**d**–**f**) Change in the GPP center of gravity of cropland, forest and grassland from 2000 to 2019). northwest, moving 0.03\({}^{\circ}\) in the meridian and 0.052\({}^{\circ}\) in latitude, and then it moved to the northeast, moving 0.063\({}^{\circ}\) in the meridian and 0.014\({}^{\circ}\) in latitude. The GPP center of gravity of the grassland continued to move to the northwest in the study period, by 0.05\({}^{\circ}\) in the meridian and 0.15\({}^{\circ}\) in latitude. From 2000 to 2019, the center of gravity of the lowest coverage shifted to the southeast, moving 0.36\({}^{\circ}\) in the meridian direction and 0.24\({}^{\circ}\) in the latitudinal direction, with a small but complex change in the inter-annual migration direction. The center of gravity of low coverage also moved to the southeast, 0.77\({}^{\circ}\) in the longitudinal and 0.24\({}^{\circ}\) in the latitudinal direction. During 2000-2008, the low coverage center of gravity first shifted back and forth to the northwest, and then folded to the southeast after 2008. The medium coverage center of gravity moved to the northwest, with a larger migration range, moving 1.24\({}^{\circ}\) in the meridian and 1.14\({}^{\circ}\) in the latitudinal direction. The center of gravity of the high coverage migrated to the northwest but migrated to the southeast first from 2000 to 2011, moving 0.157\({}^{\circ}\) in the meridian and 0.01\({}^{\circ}\) in latitude. After 2011, it migrated to the northwest, moving 0.26\({}^{\circ}\) in the meridian and 0.08\({}^{\circ}\) in latitude; the center of gravity of the highest coverage migrated to the southeast as a whole, moving 1.32\({}^{\circ}\)in the meridian and 0.53\({}^{\circ}\) in latitude (Figure 11).