## 3 Results
### Analysis of Vegetation CUE and WUE Trends in the NMR  
According to the Sen trend analysis of CUE and WUE development in the NMR (Figure 5a,c), the variation rate of CUE spanned from \(-\)0.015 to 0.019. Degrading regions (\(\theta<\) 0) in CUE accounted for 90.03% of the total area, while improving regions (\(\theta>\) 0) made up 9.97%, with the latter scattered sparsely distributed across the NMR. The WUE variation rate extended from \(-\)0.016 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\) to 0.019 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), with degrading regions covering 73.60% of the area and improving regions accounting for 26.40%, primarily concentrated in the northern parts of the NMR. The Mann-Kendall (MK) test was employed to evaluate the significance of the CUE and WUE trends, dividing the study region into five distinct groups (Figure 5b,d). The analysis revealed that approximately 64.14% of the plant cover within the research region exhibited a significant degrading trend in CUE, 3.44% showed a significant improving trend, and 11.32% remained stable. The areas showing notable enhancements in CUE were primarily located in Zhaoqing, Ganzhou, Guilin, and Meizhou. For WUE, 39.88% of the region experienced a marked declining trend, 6.72% displayed a significant improving trend, and 8.31% remained stable. Regions with significant improvements in WUE were primarily located in Chenzhou, Ganzhou, Hezhou, and Guilin. The trends in the CUE and WUE of the NMR varied significantly across different vegetation types (Figure 6). For CUE, grassland showed the largest area of improvement, which was estimated at about 2.17 \(\times\) 10\({}^{3}\) km\({}^{2}\), representing 2.39% of the entire grassland region. However, grassland also experienced the most extensive degradation, with a degraded  
Figure 4: Variation in CUE (**a**) and WUE (**b**) across different vegetation types from 2001 to 2023 in the NMR. Figure 3: Spatial distribution patterns of vegetation CUE (**a**) and WUE (**b**) in the NMR. area of 5.10 \(\times\) 10\({}^{4}\) km\({}^{2}\), representing 55.92% of the grassland area. Forests exhibited the second most severe degradation, with a degraded region of approximately 4.42 \(\times\) 10\({}^{4}\) km\({}^{2}\), which represents 72.72% of the total forest region. For WUE, grassland again demonstrated the largest improvement, with an improved area of 7.70 \(\times\) 10\({}^{3}\) km\({}^{2}\), representing 8.45% of the grassland area. Conversely, forests experienced the most significant degradation, with a degraded area of 3.97 \(\times\) 10\({}^{4}\) km\({}^{2}\), representing 65.45% of the overall forest region. Grassland followed as the second most severely degraded vegetation type, with a degraded area of approximately 2.19 \(\times\) 10\({}^{4}\) km\({}^{2}\), representing 24.05% of the overall grassland region. To gain deeper insights into the sustainability of CUE and WUE dynamics in the NMR, the Hurst exponent was calculated for pixel-level time series of CUE and WUE. Combined with the Sen analysis, the future trends and sustainability of CUE and WUE were evaluated (Figure 7). The Hurst exponent of CUE ranged from 0.231 to 0.765, while that of WUE ranged from 0.234 to 0.762 (Figure 7a,c). Areas where the Hurst exponent exceeded 0.5 comprised 95.95% of the region for CUE and 88.87% for WUE, indicating overall sustainability. Future projections show that vegetation CUE in the NMR is predominantly on a declining trajectory, with 81.67% of the area experiencing a sustained decline, widely  
Figure 5: Spatial variation rates and their significance tests of vegetation CUE (**a,b**) and WUE (**c,d**) in the NMR from 2001 to 2023. Figure 6: The area proportions of vegetation CUE and WUE trend changes for different vegetation types in the NMR. distributed across the region. Areas with a sustained increase accounted for 5.54%, mainly concentrated in Ganzhou, Guilin, and Zhaoqing. Stable regions accounted for 11.32%, primarily surrounding areas of sustained improvement.