Determining critical thresholds of ecological restoration based on ecosystem service index: A case study in the Pingjiang catchment in southern China

Considering that the degradation of ecological systems is an urgent environmental challenge, promoting multiple ecosystem services (ES) through ecological restoration has recently become more critical. However, the complicated interactions among multiple ES are not fully considered in ecological restoration planning and management, which prevents simultaneous improvements to environmental and human welfare. In this study, the spatio-temporal variations of multiple ES and their interactions were investigated in the Pingjiang catchment, which used to suffer severe soil erosion and has been the target of the ecological restoration projects. The results showed that five individual ES were heterogeneously distributed, and each individual ES and their overall benefits have increased with the implementation of ecological restoration (except for water yield). However, significantly negative correlations existed in over half of ten ES pairs, and the trade-offs among the five individual ES also increased. Through redundancy analysis, the forest proportion (FP) was identified as the major socio-ecological factor that determines multiple ES patterns; therefore, determining the appropriate FP for restoration areas is important for regulating the supply of ES. The constraint effects of FP on each ES and their overall benefits and trade-offs were examined, and inconsistent thresholds were detected for some relationships. Thus, a comprehensive index (ES index) that incorporates the overall trade-offs was proposed to reflect the complicated interactions among multiple ES and the preferences of different stakeholder groups. The constraint effect of FP on the ES index was explored, and the threshold values detected in the hump-shaped curve of the constraint lines provided references for determining the appropriate FP. This study established an integrated land use management framework by proposing a comprehensive ES index and determining its critical thresholds through the constraint line method. The results provide insights for the better planning and targeting of ecological restoration and land use management projects worldwide.