ObjectiveRestoring vegetation and combating rocky desertification on dolomite slopes in karst regions face significant challenges. The upper epikarst zone, which underlies the shallow soil layer, plays a crucial role in ecosystem processes. Nevertheless, the coupling relationships between the soil and the upper epikarst zone remain poorly understood.MethodsA representative dolomite hillslope was chosen for detailed soil-epikarst system structure investigation through trench excavation method. By integrating Kriging interpolation with geographically weighted regression analysis, the spatial distribution characteristics of different medium layers in the soil-epikarst system were analyzed. The study preliminarily proved the co-evolving feature of the soil and the underlying upper epikarst zone on dolomite hillslopes.Results1) The thickness of soil and upper epikarst zone on the dolomite hillslope gradually increased down the slope. The average thickness of the upper epikarst zone on a hillslope scale was 50 cm, with an average volume of 0.47 m³/m², accounting for 43.9% of the total volume of the soil profile, indicating that the ecological function of epikarst in karst regions is extremely important. 2) The soil-epikarst system's structure of the dolomite hillslope exhibited strong spatial heterogeneity. The spatial heterogeneity of the underlying upper epikarst zone (C+C₀=18.88) was significantly higher than that of the overlying soil layer (C+C₀=15.84); 3) The overall soil thickness, especially the B horizon's thickness, was significantly positively correlated with the upper epikarst zone's weathering degree, indicating that the increase of soil thickness promoted the weathering of the underlying upper epikarst zone, and there was a clear coupling and collaborative development relationship between soil and upper epikarst zone.ConclusionThe soil and upper epikarst zone in karst regions have evolved in a mutually reinforcing manner. The upper epikarst zone acts as an essential substrate for supporting the karst ecosystem. The soil thickness, especially the B horizon' thickness, may be critical parameters for predicting epikarst depth on karst hillslopes. In karst areas, the underlying carbonate rocks can not be ignored when carrying out soil and water resources evaluation.