Scenario analysis and relative importance indicators for combined impact of climate and land-use change on annual ecosystem services in the Karst mountainous region

Land use and climate change are important factors that help in driving changes in ecosystem services (ES); understanding the mechanisms behind the changes is critical to enhance ecosystem functions. However, the high degree of topographic heterogeneity in Karst mountainous leads to uncertainty in the spatial and temporal differences in their combined effects on ESs. To solve this problem, this study measured four ESs, the grain production (GP), carbon sequestration (CS), water conservation (WC), and soil retention (SR), taking the Qiangui Karst mountains as a case study area. The relative importance and combined effect indices were established to analyze the relative importance and interactions of year-by-year land use and climate change on ESs based on two scales of full-pixel and a simultaneous change in land use and climate. The results show a fluctuating trend of an increase in ES from 2010 to 2020, where both of them had positive and negative effects on ES fluctuation within different years. Generally, land-use change inhibited GP and enhanced other ESs, and they are facilitated by climate change. The ESs of the entire study area were mainly affected by the climate change; climate change had a stronger influence than land use on ESs in 80% of the pixels. When only the land use and climate change pixels were considered, SR was mainly influenced by climate change. The remaining ESs were mainly influenced by land-use change, but their contributions showed significant interannual differences. Their combined effect is dominated by trade-offs for GP and synergistic effects for the other ESs, with 50-75% of the areas dominated by synergistic effects. The study shows that analysis of the year-by-year spatial and temporal dynamics of ESs and their influencing factors provided more information, guiding the identification of hotspots with synergistic impact as the future priority of ecological conservation.