Changes in land use and soil retention functions in Zhangjiakou City

To elucidate the impacts of changes in the land use type use changes on soil retention capacity in Zhangjiakou City, the spatial and temporal variations in land use type and soil retention capacity from 2005 and 2015 were assessed using USLE and GIS tools. The results showed that the main land use types in Zhangjiakou were cultivated land, forests, and grasslands. Areas of forests and construction increased as the other land use types decreased from 2005 to 2015. The fastest increase in area was observed for forests, which were converted from grasslands, and the lowest decrease in area was found for cultivated land, which was converted into construction land. Meanwhile, a two-way flow between forestland and grasslands appeared. An evident difference in soil retention capacity in Zhangjiakou was found among different land use types. Grasslands were respondible for the most pronounced increase in the rate of soil retention, while forests constituted the most dramatic increase in the amount of soil retention. Soil retention amounts in grasslands and forestsaccounted for 50% of the total retention across all land use types. Soil retention capacity increased by 1.752 × 10⁷ t in Zhangjiakou City over the past 10 years, and this result could be ascribed to increased land cover. The amount of soil conservation had increased in each county over the past 10 years; Yu County witnessed the greatest increase in the amount of soil conservation, and Qiaoxi district owned witnessed the smallest increase in the amount of soil conservation among all counties. Furthermore, the soil retention capacity was lower in the northwest regions and higher in the southeast regions of Zhangjiakou City. The highest soil retention capacity was observed in Chicheng County, and Qiaoxi District exhibited the lowest soil retention capacity among all counties. Finally, soil retention capacity was evidently higher in the Bashang Regions than in the Baxia Regions, and the amount of soil retention in Bashang accounted for 80% of the total of Zhangjiakou City, and the increase in the amount of soil retention in the Bashang Regions was 1.163 × 10⁷ t. The results of this study help us to understand the changes to land use and soil retention function after the implementation of ecological engineering in Zhangjiakou City, and this provide a scientific basis for promoting ecological protection and developing soil erosion control plans in the future.