Highlights What are the main findings? A spatially explicit diagnostic framework integrating process-trend-mechanism is established using multi-period LULC data to quantify the spatiotemporal evolution of CL in a typical agro-pastoral ecotone over the past four decades. Policy regulation and socioeconomic transformation are identified as the primary drivers of cultivated land change in the farming-pastoral ecotone, exhibiting pronounced nonlinear interactive effects that surpass those of natural constraints. What are the implications of the main findings? Beyond enhancing the interpretability of CL change mechanisms through multi-source remote sensing and spatial interaction detection, this approach fosters a system-level understanding of coupled human-land interactions across ecologically fragile transition zones. The proposed ZOS framework offers a transferable strategy for adaptive governance of cultivated land in globally fragile transition zones under water-energy-food constraints and climate change.Highlights What are the main findings? A spatially explicit diagnostic framework integrating process-trend-mechanism is established using multi-period LULC data to quantify the spatiotemporal evolution of CL in a typical agro-pastoral ecotone over the past four decades. Policy regulation and socioeconomic transformation are identified as the primary drivers of cultivated land change in the farming-pastoral ecotone, exhibiting pronounced nonlinear interactive effects that surpass those of natural constraints. What are the implications of the main findings? Beyond enhancing the interpretability of CL change mechanisms through multi-source remote sensing and spatial interaction detection, this approach fosters a system-level understanding of coupled human-land interactions across ecologically fragile transition zones. The proposed ZOS framework offers a transferable strategy for adaptive governance of cultivated land in globally fragile transition zones under water-energy-food constraints and climate change.Abstract The northern agro-pastoral ecotone of China faces persistent trade-offs among cultivated land (CL) protection, energy development, water constraints, and ecological restoration, posing challenges for sustainable human-land interactions. Focusing on Yulin City from 1980 to 2020, this study develops an integrated diagnostic framework coupling pattern-process-trend-mechanism modules to analyze the spatiotemporal evolution, transition pathways, and driving forces of CL change. Results show that CL dynamics over four decades were shaped by nonlinear interactions among natural conditions, policies, economic development, and technological progress. Spatially, CL changes exhibited a distinct divergence, with ecological-driven contraction in the southern region and sandy land-based compensation in the north. Temporally, the transformation evolved from a gradual, nature-dominated stage to a policy-intensive phase characterized by abrupt shifts, followed by a refined regulation stage with multi-factor synergies. Policy interventions and economic incentives emerged as dominant drivers of CL spatial heterogeneity, with interacting factors exerting bidirectional effects. Building on these findings, a Zoning-Optimization-Synergy (ZOS) framework is proposed to support adaptive land governance, emphasizing differentiated management and cross-sector coordination. This study offers a transferable diagnostic approach for understanding CL dynamics in fragile ecotones and provides insights for managing the water-energy-food nexus under ecological transition and climate change.