Assessing ecosystem services and their spillover effects to inform cost-benefit sharing and horizontal eco-compensation mechanisms in the Qilian Mountains, China

Horizontal ecological compensation (HEC) offers many advantages over vertical ecological compensation by reducing government financial burdens, effectively addressing positive externalities and ecosystem service spillover effects, and fostering harmonious relations between upstream and downstream communities. However, a lack of reliable data remains a significant obstacle to its implementation. This study employs the InVEST model, the CASA model, the RWEQ model, and related statistical methods. Additionally, the Breaking Point Model and Field Strength Theory are used to assess eight key ecosystem services and their spillover effects at different spatial scales, with the aim of informing cost-benefit sharing and HEC mechanisms in and around the Qilian Mountains, China. Our results suggest that: (1) Soil conservation contributes the most to ecosystem services, accounting for 47.26%, followed by water retention (17.52%) and carbon sequestration (15.62%). (2) Forests (48.51%) and grasslands (39.22%) are the primary ecosystem types providing these services. (3) The ecosystem services exhibit significant internal coupling, peripheral coupling, and tele-coupling, creating spillovers at watershed, provincial, and even global scales. (4) In terms of the scope of the spillover effect, tourism and leisure lead, followed by sandstorm prevention, material production, water retention, soil conservation, flood regulation, carbon sequestration, and pollination services. From these data, we also constructed three HEC pathways: intra-provincial watersheds, inter-provincial HEC, and international HEC. Our findings are useful for developing a fair and well-functioning HEC mechanism that offers multiple environmental and social benefits, contributing to the realization of several UN Sustainable Development Goals (SGDs) such as eliminating poverty (#1), zero hunger (#2), climate action (#13), and life on land (#15).