## 4 Discussion  
### Attribution Analysis and Recommendations for NPP Changes  
The NPP in Ordos City shows an obvious increasing trend. Combined with the results of the analysis of the driving factors, the following reasons can be identified. The coal industry in Ordos City started early, but development was relatively slow. Since 2000, it has entered an era of great development after the improvement of mining technology and equipment. According to the relevant data, the number of coal mines dropped from 5502 in 2000 to 306 in 2011, but the coal production capacity increased from 26,790,000 tons in 2000 to 588,000,000 tons in 2011. The year 2012 was influenced by the economic growth rate; the demand for coal dropped, the supply of domestic coal was over capacity, and there was a drop in the price of coal. According to incomplete statistics from relevant reports, the suspension of coal production in 2014 accounted for 23% of the total coal. With the enforcement of national eco-protection policies (e.g., returning farmland to forest), Ordos City has adopted a strategy of protecting large areas and treating small areas by implementing ecological construction projects, returning pasture to grass and small watershed management [31; 32]. Figure 8 shows the temporal and spatial changes of a mining area in Ordos City, which was still mountainous in 2003 and had been mined in 2010, and in 2016, although the mine was still being mined, the area was ecologically restored accordingly and covered by green vegetation. With the growth of the economy, the total population of Ordos City, especially the non-agricultural population, shows a growing trend, which also implies an increase in the level of urbanization. As shown in Figure 9, the urban areas in Ordos City show a clear trend of expansion. The expansion of urban areas will lead to a reduction in and the destruction of vegetation to a certain extent, which in turn will affect NPP. In addition, with the increase in human population, a large amount of human activities will be carried out (e.g., burning of fossil fuels, utilization of raw coal, production of electricity, investment in fixed assets, etc. ), which will generate a large amount of carbon emissions. All of these factors have an impact on NPP. Figure 8: Spatiotemporal distribution in a mining area of Ordos City. Figure 9: Spatiotemporal distribution in urban areas of Ordos City. Ordos City belongs to the northern temperate zone of the semi-arid continental climate zone, with large temperature variations in winter and summer. The ecological environment in Ordos City is fragile. As shown in Figure 10, the mean precipitation from 2000 to 2015 showed low spatial patterns in the northwest and high spatial patterns in the southeast, and the precipitation exhibited a more obvious area of increase. From 2000 to 2015, the mean temperature showed an upward trend, with a spatial distribution of a low center and high periphery. Precipitation and temperature affect the sowing and growth of plants, and the increase or decrease in plants directly affects the amount of organic carbon fixed through photosynthesis, which consequently has an impact on NPP. From the positive correlation between the usable grassland area and NPP, it can be seen that the conservation and planting of green plants may raise Ordos City's carbon absorption capacity [33; 34]. With the execution of the national Three-North Shelterbelt Project [35; 36], Ordos City has been vigorously developing its forestry industry. It is worth noting that Ordos City is not suitable for large-scale forestry development implementation due to its location in the transition zone of semi-arid and arid areas [14]. In addition, the burning of fossil fuels, raw coal and other energy sources can produce large amounts of carbon emissions amid the development of scientific and effective energy extraction plans, as well as post-mining ecological restoration measures [37; 38; 39].