## 2 Study Area, Methods, and Data Sources  
### Study Area  
The Inner Mongolia Autonomous Region (IMAR) is an administrative region at the provincial level situated in the north-most part of China. It is characterized as one of the most typical grasslands in China and the world. Covering an area of \(\approx\)1.2 \(\times\) 10\({}^{6}\) km\({}^{2}\), 60% of the area is occupied by grassland vegetation, and most of the area is characterized as arid and semi-arid regions. There are four main grassland vegetation types [17]: meadow steppe (including _Stipa bacialensis_ and _Actnatherum splendens_, which occupy 13% of the total area), typical steppe (including _Stipa grandis_ and _Levmus chinensis_, which take 28% of the total area), desert steppe (including _Stipa klemenzii, Sheep fescue_, and _Seriphidium graclescens_, covering 12% of the total area) and steppe desert (mainly _S. sareptana_ and _S. glareosa_, covering 6% of the total area). The average temperature in the vegetation growing season (from April to September) fluctuates between 12.1 and 25.2 \({}^{\circ}\)C. The study region presents an increasing elevation from east to west, ranging from 156 m below sea level to 2800 m above sea level, with significant local variation. The annual precipitation varies spatially from less than 200 mm in the west to 600 mm in the east. The western section in IMAR is commonly in severe shortage of water (annual precipitation \(<\)200 mm) and is primarily a desert, while the middle to eastern part is a semi-arid region, which is mainly covered by typical grasslands, steppes, or meadows.  
Under the provincial administration level, IMAR is composed of 12 city-level administrative regions and 103 county-level administrative regions under the city level. The capital city of IMAR, or Huhehot, is located in the south-western part of the area (Figure 1a). The net primary productivity (NPP) of the grassland vegetation from the NPP product of Moderate Resolution Imaging Spectroradiometer (MODIS) 17A3 (MOD17A3) showed significant spatial variation in the past two decades in IMAR [18]. Generally, NPP distribution is consistent with the precipitation belts in that NPP decreases from the east to the west. However, there is also a considerable local difference in NPP that cannot be simply explained by climatic factors. Other impacts on NPP from natural environments and socio-economic activities including grassland management practices could not be neglected. The natural environments such as soil types, terrain features, and vegetation biomes types have been proved to affect NPP significantly [19; 20]. Human activities have a profound impact on NPP, both positively and negatively. For example, grassland restoration projects and fenced grazing practices have proven effective in improving NPP in some parts of the study area [21; 22]; they could potentially be optimal grassland management practices (OGMPs) and transferrable to other locations. OGMPs specifically refer to any human-related management strategies that could produce high vegetation productivity and thus sequester more carbon from vegetation. Conversely, some other activities such as over-grazing [23], unplanned urbanization [24], or large-scale coal mining [25] may reduce NPP and should be avoided. By implementing OGMPs at locations having lower NPP, RCU, which represents the loss of carbon sequestration due to unimplemented OGMPs, could improve carbon sequestration in the future.