## 3 Results  
### Spatiotemporal Variations in ANPP, PNPP, and HNPP  
In this study, we conducted a temporal and spatial analysis of the computed ANPP, PNPP, and HNPP from 2001 to 2018, spanning 18 years.  
Generally, the ANPP gradually increased from the northern to the southern part of the study area (Figure 4a). This trend became even more evident when we calculated regional statistics by province (Figure 4d). Meanwhile, the PNPP displayed a clear spatial distribution pattern (Figure 4b), incrementally increasing from the northern to the southern parts of the research area, displaying a near-circular distribution. The HNPP, on the other hand, featured a distribution characteristic of being lower in the west and higher in the east (Figure 4c).  
Figure 4: Spatial distribution of the mean (**a**) ANPP, (**b**) PNPP, (**c**) HNPP, (**d**) and ANPP after conducting regional statistics by province.  
From 2001 to 2018, the average ANPP in the research area was 677.17 gC m\({}^{-2}\) a\({}^{-1}\), showing an upward trend with an annual average increase of 4.84 gC m\({}^{-2}\) a\({}^{-1}\). The average PNPP was 1581.93 gC m\({}^{-2}\) a\({}^{-1}\), also showing an increasing trend, but with a lower annual growth rate of 0.54 gC m\({}^{-2}\) a\({}^{-1}\). The average HNPP was 900.44 gC m\({}^{-2}\) a\({}^{-1}\), displaying a decreasing trend with an annual average decline of \(-\)4.31 gC m\({}^{-2}\) a\({}^{-1}\) (Figure 5).  
On a pixel scale, the proportions of different ANPP values were as follows: \(<\)250 gC m\({}^{-2}\) a\({}^{-1}\) accounted for 7.24%, 250-500 gC m\({}^{-2}\) a\({}^{-1}\) for 22.07%, 500-750 gC m\({}^{-2}\) a\({}^{-1}\) for 30.63%, 750-1000 gC m\({}^{-2}\) a\({}^{-1}\) for 25.42%, 1000-1200 gC m\({}^{-2}\) a\({}^{-1}\) for 9.40%, and \(>\)1200 gC m\({}^{-2}\) a\({}^{-1}\) for 5.24%. Based on the distribution across different ranges, it can be observed that most of the ANPP values were concentrated in the 250-1000 gC m\({}^{-2}\) a\({}^{-1}\) range, accounting for 76.12% of the total pixels.  
The proportions of pixels for different PNPP values were as follows: \(<\)400 gC m\({}^{-2}\) a\({}^{-1}\) accounted for 3.82%, 400-800 gC m\({}^{-2}\) a\({}^{-1}\) for 1.08%, 800-1200 gC m\({}^{-2}\) a\({}^{-1}\) for 7.00%, 1200-1600 gC m\({}^{-2}\) a\({}^{-1}\) for 41.63%, 1600-1800 gC m\({}^{-2}\) a\({}^{-1}\) for 30.32%, and \(>\)1800 gC m\({}^{-2}\) a\({}^{-1}\) for 16.15%. The majority of PNPP values were primarily concentrated in the 1200-1800 gC m\({}^{-2}\) a\({}^{-1}\) range, making up 71.95% of the total pixels.  
The distribution of pixel proportions across different HNPP value ranges was as follows: less than 0 gC m\({}^{-2}\) a\({}^{-1}\) constituted 0.88%, 0-300 gC m\({}^{-2}\) a\({}^{-1}\) constituted 7.61%, 300-600 gC m\({}^{-2}\) a\({}^{-1}\) constituted 16.36%, 600-900 gC m\({}^{-2}\) a\({}^{-1}\) constituted 35.33%, 900-1200 gC m\({}^{-2}\) a\({}^{-1}\) constituted 25.16%, 1200-1500 gC m\({}^{-2}\) a\({}^{-1}\) constituted 11.24%, and over 1500 gC m\({}^{-2}\) a\({}^{-1}\) constituted 3.42%; these values were predominantly concentrated in the 300-1500 gC m\({}^{-2}\) a\({}^{-1}\) range, accounting for 88.09% of the total pixels.