Estimated ecological carrying capacity on grassland of Inner Mongolia based on the priority of ecological services

Temperate grassland vegetation can dominate in Inner Mongolia of the Eurasian steppe. These ecosystem services can support both animal husbandry and the local economy. While some ecological functions can also deliver, such as wind erosion control, soil and water conservation, hydrological regulation, and biodiversity maintenance. However, these ecosystems can be confined to the rising global temperatures and human activities. Particularly, the grassland degradation has posed a serious threat to the regional ecological security in sustainable agriculture. In this study, an ecological carrying capacity (ECC) assessment framework was proposed to maintain the essential grassland ecological services. The environmental features and ecological regulatory functions of the grasslands were also considered in Inner Mongolia. The spatial patterns of the carrying status were then quantified for the grassland animal husbandry. The grassland carrying capacity index was employed to compare the grassland ecosystems in order to support animal husbandry over different league cities. The results show that the spatial distribution of the annual average aboveground net primary productivity (ANPP_W) in grasslands of Inner Mongolia exhibited a gradual decreasing trend from the northeast to the southwest from 1991 to 2020. The highest ANPP_W values reached 60 g/(m²·a) in the Greater Khingan and Yinshan Mountain regions, which were characterized by the significant topographic relief, high soil erodibility, and strong rainfall erosivity. The ANPP_F was allocated for the wind erosion control and sand fixation, indicating the spatial pattern with the decrease from the west to the east. The ANPP_F values were higher, typically exceeding 80 g/(m²·a), in Hulun Buir, the southeastern Horqin Sandy Land, and the central Ulanqab Plateau, with the relatively flat terrain and the high surface deposits. Overall, the optimal range of the ANPP_S was required to sustain the ecosystem service functions in Inner Mongolia. There was some variation between 30 and 240 g/(m²·a), indicating the spatially decreasing gradient from the northeast to the southwest. The relatively high ANPP_S were also required to maintain the natural regeneration of the grassland ecosystems in most areas. The ECC of the grassland ecosystem was 78.65 million sheep units from 1991 to 2020, while the actual total livestock was 104.36 million sheep units. The livestock demand for the grassland resources also exceeded the supply capacity. The ecological carrying pressure index of the grasslands in the entire study area ranged from 0.62 to 8.68, and the economic carrying pressure index ranged from 0.21 to 2.79. The relatively large ANPP was occupied by the natural renewal of grasslands, thus greatly reducing the ECC of the grasslands in Inner Mongolia. Spatially, the relatively high ECC of the animal husbandry was observed in the eastern grasslands. While there was a more serious overloading of the animal husbandry in the western grasslands. The ANPP was used to characterize the provision of three ecosystem services; Some functions can also be expected to reflect the magnitude of these services, such as biodiversity maintenance, water conservation, and atmospheric purification. It is therefore necessary to incorporate the additional functional indicators of the ecosystems in order to improve the accounting framework for the ECC using ecosystem services. The framework can be expected to estimate the grassland ECC. The findings can provide the decision-making on the grassland resource utilization and regional ecology in sustainable agriculture, thereby supporting some initiatives, such as the grassland ecological compensation, grazing withdrawal, and grassland restoration.