Bidirectional interactions among ecosystem services under the Grain for Green Program: Insights from simultaneous...

Unraveling bidirectional interactions among ecosystem services is a key foundation for effective implementation of the Grain for Green Program (GFGP). Yet, prevailing methodologies fall short by either ignoring reciprocal interactions or confounding them with external drivers, leading to biased inferences. Thus, this study quantified the spatiotemporal dynamics of water yield, grain production, carbon sequestration, and soil conservation of a fragile basin in the Loess Plateau under GFGP from 2000 to 2019. Simultaneous equation models were employed to simultaneously investigate the bidirectional interactions and drivers of the ecosystem services. The results show that: 1) From 2000 to 2019, the total amount of water yield decreased, while other ecosystem services increased. 2) In 2005, water yield had a positive effect on grain production, whereas grain production constrained water yield. Water yield and soil conservation mutually constrain via runoff-erosion feedback. NPP had a negative effect on water yield in later periods due to increased transpiration. 3) The cumulative cropland to forestland conversion ratio reduced soil conservation in 2005 but increased it by 2015, due to engineering lag. The cumulative cropland to grassland conversion ratio reduced grain production in every period. These findings highlight the importance of monitoring dynamic changes in bidirectional interactions and drivers of the ecosystem services to support the scientifically sound, long-term implementation of ecological restoration projects.