## 4 Discussions
### Driving Factors for Reduced Carbon Uptake (RCU)  
The driving factors for RCU could be complex. In this study, along with NPP, the human-related factors, including grazing intensity, population, and road network density, were taken to examine their impact on RCU using both global (OLS) and local (GWR) regression models. As stated above, heavily grazing could degrade vegetation productivity. However, a recent meta-analysis of stock grazing on China's grasslands concluded that light and medium grazing was actually beneficial to grassland vegetation [50]. For example, light and moderate grazing could improve the top soil organic \begin{table}
\begin{tabular}{c c c} \hline
**OGMPs** & **Main Practices and Results** & **Study Location** & **References** \\ \hline Rotating grazing & \begin{tabular}{c} Grazing and protection rotationally \\ improved NPP \\ Replacing direct grazing with \\ grass-cutting improved NPP \\ Densely distributed roads/urbanization \\ reduced NPP in areas with dense \\ vegetation and protection zone/belt is \\ recommended \\ Restoration and recovery \\ projects \\ \end{tabular} & \begin{tabular}{c} Xilingol league in IMAR \\ Replacing direct grazing with \\ grass-cutting improved NPP \\ Densely distributed roads/urbanization \\ reduced NPP in areas with dense \\ vegetation and protection zone/belt is \\ recommended \\ Restoration and recovery \\ improvement, reduced erosion, and \\ thus improved NPP \\ Heavy coal or metal mining activities \\ reduced NPP, and vegetation restoration \\ should be followed after mining \\ Certain amount of irrigation improved \\ NPP \\ \end{tabular} & \begin{tabular}{c} Xilingol league in IMAR \\ Xingol league in IMAR; \\ Xingol league in IMAR; \\ Horqin sandy land in IMAR \\ \end{tabular} & [35; 45; 46] \\ \hline Vegetation protection & \
\begin{tabular}{c} Heavy coal or metal mining activities \\ reduced NPP, and vegetation restoration \\ should be followed after mining \\ Certain amount of irrigation improved \\ NPP \\ \end{tabular} &
\begin{tabular}{c} Eastern IMAR \\ Xilamuren grassland (in \\ middle to western IMAR) \\ \end{tabular} & [25] \\ \hline \end{tabular}
\end{table} 
Table 5: Typical examples of optimal grassland management practices (OGMPs) in Inner Mongolia. carbon, which is essential for vegetation growth [51]. The impact from grazing is also related to vegetation status and terrain features [35]. The above findings suggest that grazing may impose different effects on NPP under different local conditions. The current study verified that grazing intensity showed a positive impact on NPP in the northern and north-eastern parts of the study area (Figure 5a). Hence, optimal grazing intensity must be decided considering the location difference. The population or the total number of human inhabitants reflects the socio-economic development of the area. Densely distributed population was found to have reduced carbon sequestration from vegetation (i.e., increased RCU) in some parts of the grassland; this is understandable, because more population means a sprawl of human settlements and built-up areas, which could easily fragment and degrade grassland vegetation [52]. Previous work verified that the impact of roads on grassland vegetation depends on the nature of the resource (e.g., the density of vegetation cover) [43]. This study found that the grassland vegetation responded differently to the impact from roads at various locations, suggesting that the grassland management policy should reflect the location-dependent impact from the road network. The current work reveals the associations between the selected variables and RCU, but the patterns in the cause and effect need further field verification in the future. This work is limited to examining the impact of some commonly recognized human-related factors on RCU; however, they together only explain slightly over half of the variance in RCU (53%), which could be further improved.