The Beijing-Tianjin sandstorm source control project (BTSSCP) is a large and famous ecological construction project with enormous investment that aims to improve and optimize the ecological condition of Beijing-Tianjin and the surrounding areas. Since the implementation of the BTSSCP in 2000, profound changes have occurred in the region regarding land use, vegetation cover, soil, wind and water erosion, and the supply of regional ecosystem services (ESs). Changes in regional ESs are influenced not only by human activities but also by natural factors such as climate change. Distinguishing and quantifying the roles of climate change and land-use change on regional ES changes can better serve sustainable land-use management decisions at the regional and national levels. Additionally, information is needed on the economic benefits caused by sandstorm control and ecological restoration, such as the value change of the regulating ESs since the BTSSCP began, the variation in the spatial patterns of ESs and their integration, and the contribution of sand control and vegetation restoration to regional ES changes. Moreover, a landscape-level ES multifunctionality concept and measurement framework provided deep insight into the spatial supply-benefit relationship of ESs, and this information is crucial for sustainable ecosystem management and land-use planning. In this study, a set of ES indicators that represent ecological provisioning (n=2), regulating (n=4), and supporting (n=2) services at the county scale in the BTSSCP were calculated based on a field survey, Normalized difference vegetation index (NDVI) data, land-use data, meteorological data (i.e., temperature, precipitation, wind speed, and direction) and socioeconomic census data. Then, the ES multifunctionality of each county was assessed using the multiple ES landscape index (MESLI) and the ES Shannon diversity index (ESHDI). Variation partitioning was used to distinguish the contributions of land-use area composition and major climatic conditions (annual average temperature, annual precipitation, and average wind speed) to various ESs, and the MESLI and ESHDI in different periods were measured and compared. Partial least squares path modeling (PLS-PM) was applied to determine the direct and indirect effects of the BTSSCP on the regional ecological supply, ecological regulation, habitat support services and multifunctional indicators of ESs and their changes. The results showed that (1) the implementation of the BTSSCP effectively improved the regulating ESs in Beijing, Tianjin and surrounding areas and promoted the overall improvement of the comprehensive benefits of regional ESs while effectively improving the integration and diversity of ESs in the core areas of wind and sand management. The MESLI increased in 94.8% of all counties in 2015 compared to 2000. (2) Both land-use composition and climatic factors had impacts on the regional ES provisions, but the influence of land use on the regulating and provisioning ESs was significantly higher than that of climatic factors. The direct effect of land use on ES provision, regulation, and support was enhanced, the multifunctionality of regional ESs was dramatically improved, and the role of climatic factors markedly declined as the project proceeded. (3) The economic benefits of the BTSSCP were positive, with a 415300 yuan/km2 increase in the content of regulating ESs, and 82.7% of counties had reduced wind erosion after BTSSCP implementation, which indicated that the comprehensive economic benefits of BTSSCP implementation were significant. These results provide a scientific basis for evaluating the benefits of the BTSSCP and serve as a reference for developing new national management strategies.
