## 3 Results
### The Changing Trend in NEP  
Since 2000, the spatial and temporal changes in vegetation carbon sinks in the Taihang Mountains have been obvious. Over time, the vegetation carbon sink in the Taihang Mountains as a whole shows an increasing trend (Figure 5). Among them, the area of regions with an average vegetation carbon sink value of more than 300 gC\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\) increased from 20% in 2000 to 60% in 2022, especially Zhangjiakou, Taiyuan, Linfen, and Jincheng, which had the most obvious changes in growth, indicating that the growth environment of vegetation in those regions had been improved, the types of vegetation had become more abundant, and the amount of carbon sequestered by vegetation had been significantly increased. In addition, the area of low-carbon sinks in the eastern Taihang Mountains has been shrinking, with more than 50% of the area with an average vegetation carbon sink value of less than 250 gC\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\) in 2000, and less than 20% of the area with low-carbon sinks by 2022. Over time, the vegetation carbon sinks in Fangshan in Beijing and Baoding and Xingtai in Hebei within the Taihang Mountains region have increased significantly, while other parts of the region, including Shijiazhuang, Handan, Anyang, and Xinxiang, are influenced by geographic and topographical factors, and the vegetation types are mostly cultivated vegetation, with plains, farmland, and cropland dominating, so that this part of the region contributes to the carbon sinks to a relatively low degree. Based on the Theil-Sen Median slope estimation, the inter-annual trend and spatial distribution of significance of vegetation carbon sinks in the Taihang Mountains were obtained from 2000 to 2022 (Figure 6), and the proportion of areas with positive NEP values accounted for more than 80% of the total area, indicating that the vegetation carbon sinks in  
Figure 4: Time series changes in the mean value of NEP in the Taihang Mountains from 2000 to 2022. Figure 5: Comparison of the mean values of NEP in the Taihang Mountains from 2000 to 2022.  
the Taihang Mountains have shown an overall increasing trend over the 23 years. Among them, the areas with significant inter-annual trends were concentrated in the northeastern and western mountain range areas of the Taihang Mountains. The Theil-Sen Median analysis and MK test results were superimposed into five categories (Table 2), Based on the Mann-Kendall test to visualise the inter-annual trend of significantly changing NEP, it is more intuitive to obtain the trend of significant increase in the overall NEP in the Taihang Mountains Region, and almost the whole region of the vegetation carbon sink had a significant growth trend; only a small part of the peri-urban areas bordering Beijing, Shanxi, Hebei, and Henan provinces and cities were significantly affected by the anthropogenic factors, and the fluctuation of NEP was large, the stability was poor, and the trend of the decrease was more significant. The spatial distribution of the coefficient of dispersion of vegetation carbon sinks is shown in Figure 7, with the exception of a few areas, all of which are less than 1. The proportion of areas with coefficients of dispersion of less than 0.1, 0.1-0.3, and 0.3-0.5 in the total area of the vegetation area is 5.9%, 91.6%, and 1.9%, respectively, which suggests that the overall fluctuation of the region's vegetation carbon sinks over time is relatively small, and the stability of the region is relatively high. In terms of spatial distribution, the coefficient of dispersion of vegetation carbon sinks is high in the northeast and low in the west-central direction, and the high fluctuation areas are scattered, mainly in the border of Beijing, Shanxi, and Hebei provinces, the junction of Shijiazhuang, Jinzhong, and Yangquan, and the periphery of Jincheng, Xinxiang, and Jiaozuo, which have a low stability of vegetation carbon sinks and are vulnerable to the influence of natural or human activities.