## 3 Results
### Spatiotemporal Variation Characteristics of Vegetation in Xinjiang
#### 3.2.3 Spatiotemporal Distribution Characteristics of Natural Forest grasslands in Xinjiang  
The distribution of natural forests and grasslands in Xinjiang was extracted based on land cover data from 2000 to 2020 (Figure 8a). The results showed that natural forests and grasslands were primarily located in ecological regions R1, R3, and R5. Forest areas occupied the smallest proportion (1.25%) and were mainly concentrated in the mountainous  
Figure 7: Spatial distribution of correlation coefficients for NDVI and SIF from 2000 to 2020 in Xinjiang. (**a**) Spatial distribution of the correlation coefficient between NDVI and SPEI across pixels over the study period. (**b**) Spatial distribution of the correlation coefficient between SIF and SPEI across pixels over the study period. The color scale represents correlation values from \(-1\) to \(1\), where blue areas indicate a strong positive correlation and red areas indicate a strong negative correlation. The inset bar chart shows the proportion of pixels with positive and negative correlation trends.  
regions of R1 and R3. Grasslands, which cover the largest area, were classified into three categories based on coverage. High-coverage grasslands (>50%) account for 22.51% of the total and are mainly located in the R1 and R3 regions, where moisture availability is relatively high. Medium-coverage grasslands (20-50%) cover 22.46% of the area and are more widely distributed, although with less favorable moisture conditions. Low-coverage grasslands (5-20%) occupy the largest area, covering nearly half of the grasslands of Xinjiang. Due to prolonged moisture deficits, low-coverage grasslands exhibit sparse vegetation structures. Figure 8b illustrates the changes in the spatial distribution of natural forests and grasslands in Xinjiang between 2000 and 2020. The results indicated minimal change in the overall forest and grassland areas, with an increase of 25.77% and a decrease of 24.97%, suggesting a slight net expansion (25.77% > 24.97%). Spatially, the vegetation increase was notably higher than the decrease in the R1 and R5 regions, whereas in the R2 and R4 regions, the decrease outpaced the increase. The vegetation cover in R3 remained relatively stable.  
Temporal trend analysis indicated differing change patterns in the NDVI and SIF values for natural forests and grasslands. As shown in Figure 9, the regression analysis for NDVI revealed a strong upward trend, particularly in forested areas. Conversely, the SIF values for forests exhibited a slight decline, whereas grasslands showed a modest increase. Throughout the study period, the NDVI and SIF values for grasslands remained consistently lower than those for forests, suggesting both consistency and divergence between NDVI and SIF in reflecting vegetation conditions.  
Figure 8: Spatial distribution and changes in vegetation types from 2000 to 2020 in Xinjiang. (**a**) Spatial distribution of vegetation types, including forest, high-coverage grassland (HCG), moderate-coverage grassland (MCG), and low-coverage grassland (LCG). (**b**) Spatial distribution of vegetation change over the study period, identifying common, increased, and decreased areas. The bar chart inserted shows the percentage of each type.