Balancing act in large-scale environmental restoration project: Ecological return and cost-efficiency over 18 years in a Forest-steppe ecotone project

In response to negative impacts of human disturbances, governments and international organizations have launched large-scale environmental restoration programs to mitigate ecological degradation. However, few studies have assessed these projects from a cost-efficiency perspective. In the context of increasing global macroeconomic uncertainty, such projects face mounting challenges to their financial sustainability, underscoring the need for systematic evaluations of their cost efficiency. This study takes the forest-steppe ecotone project within China's Three-North Shelter Forest Program as a case study. Using 18 years of project implementation data, we establish an evaluation framework that integrates ecological returns and cost efficiency to assess project effectiveness. The results show that from 2002 to 2019, the forest area in the project region increased by 5.32 %, while sand-fixing capacity rose from 2.00 × 10 11 tons in 2005 to 4.39 × 10 11 tons in 2019. In terms of cost efficiency, the total investment in afforestation from 2002 to 2019 ranged from CNY 341.134–391.537 billion, with an average annual investment of CNY 18.952–21.752 billion. Sub-regional analyses revealed that the Liao River Basin and Taihang Mountains zones exhibited relatively lower ecological returns. Correlation analysis indicated strong relationships between afforestation cost and sand-fixing capacity in certain regions (|cor| = 0.89–0.91), moderate correlations in others (|cor| ≈ 0.59), and weak correlations in some areas (|cor| ≈ 0.47), accounting for 1.58 %, 6.19 %, and 7.62 % of the total area, respectively. These findings establish a preliminary cost-effectiveness evaluation framework, highlighting the linkages between financial investments and ecological benefits. Regions showing positive correlations demonstrate high ecological payoffs from investment, while negatively correlated areas suggest issues of diminishing returns and resource misallocation. • Focus on the sustainability of large-scale environmental restoration project. • Linking ecological return assessment and cost-efficiency analysis. • Identification of low-efficiency area for sand fixation. • Engineering cost-efficiency analysis at pixel level. • Correlation analysis between investment and windbreak-sand fixation benefits.