Energy modeling simulation of changes in ecosystem services before and after the implementation of a Grain-for-Green program on the Loess Plateau-A case study of the Zhifanggou valley in Ansai County, Shaanxi Province, China

Understanding the relationship between land use change and ecosystem services is critical for achieving sustainable ecosystem services and for developing scientifically effective eco-conservation policies. The Zhifanggou watershed is a typical hill and gully region on the Loess Plateau that has experienced a process of serious damage and rapid recovery in recent decades, and the accompanying land use changes have been dramatic. Taking the Zhifanggou watershed as an example, this study built an energy flow model for the watershed considering croplands, woodlands and grasslands as components. This study evaluated the changes in ecosystem service values before and after the implementation of a Grain for Green (GFG) program using the method of equivalent value factor per-unit of ecosystem area. Then changes in ecosystem service values in the Zhifanggou watershed were simulated. The results were as follows: (1) the total value of ecosystem services showed a linear increase (P < 0.01) from 1995 to 2010, increase 44.2% over this time. In addition, the provisioning, regulating, supporting and cultural service values showed a cooperative growth trend (P < 0.01). (2) The change in ecosystem service values in the watershed was very small over the period examined and if the GFG program continues, it will stabilize after a slight net increase. Provisioning services showed a downward trend, while regulating, supporting and cultural services show an upward trend, furthermore, provisioning services showed a trade-off relationship with the other three services (P < 0.01). (3) If the cycle of deforestation and reclamation to agriculture continues, the ecosystem service values will decrease by approximately 83% in the next 30 years, the ecosystems will be seriously damaged again, and the values of all four types of ecosystem services will show a decreasing trend (P < 0.01). In general, the ecological environment of the Zhifanggou watershed has been stabilized by the Grain for Green program. However, the government's scientific and rational policies to ensure that the GFG program results are not destroyed and to achieve stable and sustainable development on the Loess Plateau are still needed.