Revealing trade-off and synergistic relationships among ecosystem services plays a key role in ensuring a stable ecosystem for long-term development. It is the crucial precondition for realizing watershed protection and high-quality development. The variations in land use during 1990–2020 are investigated by taking the typical areas for returning farmland to forests as an example. The spatiotemporal distributions of six key ecosystem services, namely carbon storage, water yield, net primary productivity (NPP), soil conservation, habitat quality, and forest recreation are quantified by the InVEST model and statistical data. We also uncover the spatial difference in the ecosystem in Loess Plateau, located in northern Shaanxi, with hot spot analysis and probe the trade-off and synergistic correlations among the investigated ecosystem services. The results show that: (1) the farmland decreased dramatically. On the contrary, the forests and orchards increased significantly. (2) During the same period, carbon storage and habitat quality increased, and water yield, NPP, soil conservation, and forest recreation initially declined, but subsequently rose to higher values than that in 1990. All these services in the southeastern part of the research area surpass those found in the northwest. (3) The ecosystem services relationships in northern Shaanxi are mainly characterized by synergistic correlations, which became stronger from 1990 to 2020. The trade-off effects mainly occur among the water yield and other ecosystem services and are distributed in the west and north of the investigated area. Based on these findings, this work provides scientific principles for improving the ecological environment and enhancing the resource sustainability of the study area.

In order to evaluate ecological technology scientifically, we constructed a modular “three-stage evaluation method” based on qualitative evaluation, semiquantitative evaluation and quantitative evaluation, and established the theoretical models of the four kinds of ecotechnology, such as soil and water conservation technology, desertification governance technology, rocky desertification governance technology and ecological restoration technology. We gave the quantification criteria of the first-level and second-level index commonly shared by four kinds of ecotechnology and defined the quantification criteria of the third-level index of reflecting the heterogeneity of soil and water conservation technology. An ecotechnology evaluation model combining Analytic Hierarchy Process and Logistic regression was established based on soil and water conservation technology. The rationality of the evaluation method and model were verified by field investigation data of soil and water conservation technology in Gaoxigou. The evaluation method and model could provide scientific basis for the effective introduction and popularization of ecotechnology.

Understanding the synergic relationship between the Grain for Green Program (GGP) and the agricultural eco-economic system is important for designing an optimized agricultural eco-economic system and developing a highly efficient structure of an agricultural industry chain and a resource chain. This study used Ansai County time series data from 1995 to 2014, applied vector autoregressive (VAR) models and used tools such as Granger causality, impulse response analysis and variance decomposition, to explore the synergy between the GGP and the agricultural eco-economic system. The results revealed a synergic and reciprocal relationship between the GGP and the agroeconomic system. The contribution of the GGP to the agroecosystem reached 34%, which was significantly higher than either its largest contribution to the agroeconomic system (20.8%) or its peak contribution to the agrosocial system (26.7%). The agroeconomic system had the most prominent influence on the GGP, with a year-round stable contribution of up to 55.3%. These results were consistent with reality. However, the impact of the GGP on the agricultural eco-economic system was weaker than the effect of the agricultural eco-economic system on the GGP. The lag of variable stationarity after the shock was relatively short, indicating that optimal coupling had not formed between the GGP and the agricultural eco-economic system. On the basis of enhancing the ecological functions, we should construct the agricultural industry-resource chain such that it focuses on promoting the effective utilization of resources in the region. In addition, the development of a carbon sink industry can be used to manifest the ecological values of ecological functions.