Abstract: Exploring the spatiotemporal variations, scale effects, and underlying drivers of the supply-demand relationship of ecosystem services in karstic, ecologically fragile regions is essential for improving regional ecosystem services, balancing relationships, and formulating diverse regulatory plans. In this study, we focused on four types of ecosystem services: soil conservation, water yield, carbon sequestration, and food supply. We analyzed the spatiotemporal variation in the supply, supply-demand relationships, and the scale effect of the spatial differentiation of ecosystem service supply-demand relationships in Guizhou Province. Furthermore, we elucidated the spatial differentiation mechanism of ecosystem service supply-demand relationships at the optimal scale according to the exploratory spatial analysis and the optimal parameters-based Geographical Detectors Model. The results showed that: (1) the supply and demand of the four ecosystem services increased from 2000 to 2020. All ecosystem services except water yield were in surplus, and the surplus status decreased over time. (2) The supply-demand relationships of ecosystem services showed spatial variations. The regions with a high value of soil conservation supply and demand were mainly distributed on the edge of the study area with high vegetation coverage, while those with a low value of soil conservation supply demand were mainly located in the hinterland. The regions with a high value of supply and demand of water production, carbon sequestration, and food supply were scattered in the central towns/cities, whereas those with low values were distributed throughout the region. The supplydemand surplus in the eastern regions with low elevation and high vegetation coverage was more pronounced than that in the eastern regions. (3) The comparative analysis of the scale for the four ecosystem service types, which included eight levels, indicated that the township was the most suitable scale for analyzing the spatial differentiation of ecosystem service supply-demand relationship. This scale reflected more diverse supply and demand characteristics of ecosystem services. (4) At the township scale, population density, normalized difference vegetation index, and gross domestic product were the main forces causing spatial differentiation of ecosystem service supply-demand relationships. The interaction between different forces was higher than that of single force, with slope and population density being the most prominent. This study quantitatively identified the optimal scale for ecosystem service supply and demand divergence and the underlying drivers for this scale through multi-scale analysis, providing a scientific basis for the accurate implementation of ecological restoration projects in karst regions.

Key words: ecosystem services, supply and demand, spatial differentiation, scale, driving mechanism, optimal parameters-based geographical detector model