Where Are the Trade-Offs in Multiple Ecosystem Services in the Process of Ecological Restoration? A Case Study on the Vegetation Restoration Area in the Loess Plateau, Northern Shaanxi

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.