Abstract: Quantifying the spatiotemporal patterns and driving mechanisms of ecosystem services in the agro-pastoral transition zone of northern China is crucial for maintaining their regional ecological barrier functions and achieving sustainable land management. Based on the InVEST, CASA, and RWEQ models, we evaluated five key ecosystem services (food production, carbon sequestration, soil and water conservation, windbreak and sand fixation, and water yield) from 2000 to 2020 in the agro-pastoral transition zone of northern China, and further combined spatial statistics and machine learning methods to reveal their spatiotemporal differentiation characteristics and dominant driving factors. The results showed strong spatial variations. High-value areas of food production were distributed in the eastern plains, while high-value areas of carbon sequestration and soil and water conservation were stably distributed in the southern region and along mountain ranges. High-value areas of windbreak and sand fixation were located in the north, and high-value areas of water yield were mainly situated in the south and west. From 2000 to 2020, ecosystem services displayed stage-specific evolutionary characteristics. Food production increased continuously, with the total volume growing from 2.32×10⁷ t to 6.53×10⁷ t. Carbon sequestration generally increased, rea-ching a peak of 10.7×10⁷ t in 2015 before slightly declining. Soil and water conservation fluctuated upward, reaching a high value of 3.63×10⁹ t in 2010, decreasing slightly in 2015, and then peaking at 4.03×10⁹ t in 2020. Water yield rose slowly and tended to stabilize after 2010. Windbreak and sand fixation changed most drastically, first decreasing from 4.28×10⁹ t in 2000 to 2.98×10⁹ t in 2010, and ultimately rising to 14.7×10⁹ t in 2020. The driving mechanisms for each ecosystem service were distinctly differentiated. Precipitation was the strongest positive driving factor for water yield (SHAP value was 67.95). Elevation dominated the spatial distribution pattern of food production (SHAP value was 64.47). Slope showed a strong negative association with soil and water conservation (SHAP value was 38.28). Wind speed was the primary limiting factor for windbreak and sand fixation (SHAP value was 7.02), and its changes were jointly driven by wind speed and the positive contribution of precipitation. Carbon sequestration showed negative associations with nitrogen deposition, wind speed, and precipitation. Ecosystem ser-vices in the agro-pastoral transition zone of northern China exhibited spatiotemporal heterogeneity, with synergetic and trade-off relationships coexisting among different services, reflecting multifunctional coupling. Based on the differences in driving mechanisms between natural conditions and human activities, regional ecological management should implement zoned and classified regulation to optimize the structure of ecosystem services.

Key words: ecosystem service, agro-pastoral transition zone of northern China, trade-off and synergy, multi-service relationship, driving mechanism