Yuan Li Zhongyuan Mao ^* Bin Xu ^* Yuxuan Wan ^*

• Institute of Forestry Science and Technology Information, Chinese Academy of Forestry Sciences, Beijing, China

The Loess Plateau is one of the regions in China where soil erosion and desertification are severe. Climate change and human activities have intensified the ecological security threats on the Loess Plateau. This article reveals the time lag effect of ecological engineering construction on the ecosystem service capacity index of the Loess Plateau, providing decision-making reference for improving the quality of ecological engineering and ecological security in the research area, and is of great significance for building a strong ecological security barrier on the Loess Plateau. This article analyzes the spatiotemporal changes of ecosystem service capacity index in the context of ecological engineering implementation on the Loess Plateau based on Analytic Hierarchy Process, Quantitative Index Method, Spatial Correlation Analysis Method, and Bidirectional Fixed Effects Model. The results indicate that:; 1) The vegetation coverage on the Loess Plateau increases with the increase of ecological engineering area, showing a decreasing distribution pattern from southeast to northwest in space; 2) The water conservation capacity index, wind and sand fixation capacity index, biodiversity capacity index, and comprehensive service capacity index of the Loess Plateau showed exponential growth from 2000 to 2020, and were highly coupled with changes in vegetation coverage area in time and space; 3) The spatial distribution of cold and hot spots in the ecosystem service capacity index of the Loess Plateau shows a stepwise decreasing trend of "hot in the south and cold in the north"; The hotspots and sub hotspots exhibit a reciprocating cycle from aggregation to fragmentation in time and space; Cold spots and sub cold spots are mainly concentrated in the northwest region. 4) The changes in the ecosystem service capacity index of the Loess Plateau are mainly influenced by factors such as cumulative engineering implementation area, urbanization rate, precipitation, etc. The ecological engineering construction on the Loess Plateau has achieved significant results. The increase in vegetation coverage area and ecosystem service capacity index from 2000 to 2020 has promoted the restoration of ecosystem functions. Therefore, ecological engineering construction should be actively promoted to provide scientific decisionmaking references for solving regional ecological security issues.