From a Topographic Gradient Perspective: Ecosystem Service Effects of Agricultural Land Transformation in Karst Mountainous Areas—A Case Study of Puding County, Guizhou Province

Agricultural land transformation significantly affects ecosystem services (ES), yet its impacts across different topographic gradients remain unclear, hindering integrated land management in karst mountainous areas. Using Puding County, Guizhou Province, as a case study, this research employed the land-use transfer matrix, the InVEST model, and Spearman correlation analysis to examine the spatiotemporal patterns and relationships between agricultural land transformation and ES from 2004 to 2024. The findings indicate: (1) Agricultural land transformation shows distinct topographic differentiation: non-agricultural conversion and agricultural intensification dominate low-topographic positions; ecological land use conversion and agricultural intensification coexist in mid-topographic positions; and ecological land use conversion prevails in high-topographic positions. (2) ES vary consistently along topographic gradients: soil retention and carbon storage increase with elevation, food supply concentrates in low topographic positions, and water yield changes are most pronounced at low topographic positions. (3) Topography regulates the ecological effects of transformation pathways: ecological land use conversion enhances regulating services in high-topographic positions, while farmland abandonment increases erosion risk; composite transformation promotes a dynamic balance between services in mid-topographic positions; and agricultural intensification improves food supply but intensifies water competition in low-topographic positions, whereas non-agricultural conversion degrades multiple ecosystem services. This study provides a scientific basis for zoned land management and sustainable development in karst mountainous areas.