## 4 Discussion  
### What Are the Spatial Patterns of Land Use and Land Cover under Different Scenarios?  
The A2 and B2 scenarios showed a significant increase in the cropland and built-up area at the cost of constant environmental deterioration during 2010-2100. Compared with the A2 and B2 scenarios, the environment-oriented A1B scenario demonstrated a slower rate of urbanization with a rapid boost in rangeland and woodland, because of the replacement of cultivated land and rangeland with woodland as well as the effective ecological conservation policies, for example, Grain for Green Program, and 2001-2050 National Grassland Ecology Protection and Construction Program. The B1 scenario is in accordance with the environment-oriented A1B scenario. Although facing a range of trajectories of future LULC, a great quantity of previous studies have reached comparable agreement concerning plausible future LULC scenarios under the IPCC SRES scenario at local and regional scales [72; 73]. Concerning A2 as an illustration, they believed that the growing requirement of a bigger residential space, and weaker spatial planning is expected to frequent, as well as intensive land use conversion [74; 75; 76]. As to B1, it was expected that land use conversion per capita would decrease and urban sprawl would minimize, benefiting from more stringent spatial planning management, high fuel prices, and attractiveness of medium-sized cities with convenient public transportation connecting to larger cities [76].  
Without concerning the IPCC SRES storyline employed, plenty of previous studies reported that a large reduction in agricultural land results from the decoupling between population growth and increase in agricultural production due to agro-technological development [66]. Besides, under all the four scenarios, sandy land and sparsely vegetated land in the north-west region in the vicinity of Lanzhou city are expected to be restored to grassland, especially in 2100. Some research reported that the vegetation in sand desert is relatively insensitive to the climate change compared to other sub-regions in APTZNC, possibly because of its high tolerance of extreme climate [77], and its previous adaption to a dry and cold environment, like water shortages [78]. Therefore, under environmental protection scenarios (A1B, B1), the demands for ecological lands are expected to increase. The sparsely vegetated land in arid areas in the west may be easily restored to grassland since the grasslands in the eastern water-rich areas may be replaced by woodland. Furthermore, under scenarios A2 and B2, the bare land also might be converted to grassland since some high-quality grasslands are occupied by urban land. This implies that although the quantity of ecological land has reached the demand, land planners and policy makers should pay more attention to the quality of ecological land.  
The demand for sunlight, temperature, and water of different land use types has shaped the current spatial heterogeneity. Grasslands are predominately found in the arid and semiarid regions of the Inner Mongolian with less precipitation. Agricultural crops have high solar and water requirements; thus, they are distributed in humid areas in the east. They predominantly feature flat terrain, better natural ecological conditions, superior irrigation condition, and highly concentrated populations.  
Figure 7: The trade-offs between different ecosystem functions on the landscape level. The relationships between (**a**) NPP (unit: g C m\({}^{-2}\) a\({}^{-1}\)) and ERO (unit: g m\({}^{-2}\) a\({}^{-1}\)), (**b**) SOM (unit: g kg\({}^{-1}\)) and ERO (unit: g m\({}^{-2}\) a\({}^{-1}\)), and (**c**) TN (unit: mg kg\({}^{-1}\)) and ERO (unit: g m\({}^{-2}\) a\({}^{-1}\)) in 2010.  
Forests have played a role in windbreak and sand fixation, which are mainly distributed in the edge forest areas, especially after the implementation of regional afforestation policies.