## 3 Results
### Gravity Center Migration of Vegetation NPP
The long axis of the standard deviation ellipse was 19.735 km in the north-south direction, and the short axis was 3.532 km in the east-west direction. The ratio was 5.59, indicating that the dispersion in the north-south direction was greater than that in the east-west direction. From the polar coordinates, it can be observed that the gravity centers in the northern quadrant had the largest proportion of 65%, indicating that the vegetation NPP increments in the northern half were higher than that in the southern quadrant. From the perspective of distance, in 2000 and 2001, it was far from the origin, and the distances were 27.237 km and 39.186 km, respectively, indicating that the vegetation NPP increased significantly in the corresponding areas in these two years. In 2006 and 2007, it was close to the origin, and the distances were 3.08 km and 0.69 km, respectively, indicating that the vegetation NPP did not fluctuate much. Figure 7a shows that the vegetation NPP gravity centers in Northeast China showed a migration trend of southeast-northwest-northeast-southwest from 2000 to 2022. From 2001 to 2005, the gravity center shifted to the southeast compared with that of 2000, indicating  
that the vegetation NPP increments in the south were greater than those in the north. The vegetation NPP gravity center from 2006 to 2010 and 2011 to 2015 shifted to the northwest compared with that of 2001-2005, indicating that the increments of vegetation NPP in the northwest were greater than those in the southeast during the study periods. From 2016 to 2020, the gravity center shifted slightly to the northeast, indicating that the growth and increments of vegetation NPP in the northeast were greater than those in the southwest. From 2021 to 2022, the vegetation NPP gravity center shifted significantly to the southwest, indicating that the growth and increments of vegetation NPP in the southwest were greater than those in the northeast. On the whole, the vegetation NPP gravity center showed a trend of rotating from north to south to north and then moving south. However, the distance moving south was greater than that moving north, which indicates that the growth rate and increments in the south of Northeast China in the past 23 years were greater than those in the north. Figure 7: _Cont._  
Figure 7b shows that the gravity center migration trajectory of vegetation NPP in East China showed a trend of moving northwestward. During 2001-2005 and 2006-2010, the northwest migration distances were the largest, at 18.312 km, indicating that the growth rate and increments of vegetation NPP in the northwest direction were the largest during this period. During 2006-2010 and 2011-2015, the migration distances of the gravity center of vegetation NPP were the smallest, at 0.768 km, indicating that the growth rate and increments of vegetation NPP in the northwest direction were the smallest during this period. Figure 7c shows that the vegetation NPP gravity centers in Southwest China moved northeastward in the first three periods and then moved northwestward in the last two periods. The five periods are 2000\(\rightarrow\)2001-2005, 2001-2005\(\rightarrow\)2006-2010, 2006-2010\(\rightarrow\)2011-2015, 2011-2015, and 2016-2020\(\rightarrow\)2021-2022. During 2006-2010 and 2011-2015, the migration distances were the largest, at 13.914 km, but the migration angle to the northeast was smaller, indicating that the growth rate and increments of vegetation NPP in the northeast direction were greater than those in the southwest direction during this period. During 2011-2015 and 2016-2020, the migration distances were the smallest, at 2.615 km. Overall, the gravity centers of vegetation NPP in Southwest China moved to the northeast, indicating that in the past 23 years, the increments of vegetation NPP in the northeast parts were greater than those in the southwest parts. Figure 7d shows that the migration trajectory of the gravity centers in Northwest China was relatively complex. In 2001-2005, the vegetation NPP gravity center moved to the northeast.