Trade-Offs and Synergies in the Species–Carbon–Water–Food–Economy Functional Nexus in China’s Provinces from a Socio-Ecological System Perspective

Understanding the complex and evolving interactions between ecosystem services and socio-economic development is crucial for addressing ecological challenges and achieving harmony between humans and nature. However, multi-objective nexus optimization models that reveal the interdependencies of socio-ecological systems have received little attention. This study therefore aims to propose a species–carbon–water–food–economy functional nexus and explore trade-offs and synergies across China’s provinces from 2000 to 2020, using the InVEST model, correlation analysis, and redundancy analysis. The results revealed that the species protection function exhibited an “increase–decrease” trend, while the carbon sink, water conservation, food supply, and economic development functions increased. Both ecosystem functions and economic development functions exhibited spatial differences. Although synergies dominated the functional nexus, a trade-off was observed between species protection and food supply, with functional interactions showing spatial heterogeneity at the provincial scale. Complex interactions between social systems and ecosystems were observed in 2000, 2010, and 2020, with explanatory powers of 52.5%, 59.7%, and 59.1%, respectively. Functional policy goals exhibited both trade-offs and synergies. To achieve the sustainable development of the socio-ecological system, a “multi-goals driven, multi-sectoral linkage, and multi-policies synergy” framework should be implemented to balance the species–carbon–water–food–economy functional nexus.