Quantifying trade-offs of land multifunctionality evaluated by set pair analysis in ecologically vulnerable areas of northwestern China

Land systems in drylands have been experiencing increasing conflicts among multiple land functions. The improvement of one function is often at the cost of other functions, and trade-offs occur. Previous studies often cannot adequately address the fuzziness and lack an optimal benchmark when assessing land multifunctionality, and neglect the nonlinear features when quantifying the trade-offs. Taking the Heihe River Basin (HRB) in China as a study area, we applied the set pair analysis (SPA) to develop a novel framework for assessing land multifunctionality at a grid scale from the production-living ecological aspects. We then utilized the constraint line fitted with segmented quantile regression to identify the trade-offs among land functions. The results showed that our developed model could effectively measure land multifunctionality. The overall land multifunctionality in the HRB increased between 2000-2015, and the increased production and living functions made more contributions. From 2000 to 2015, the relationship between production function and ecological function changed from the status of synergy to trade-off, and the degree first increased and then decreased. The coupling coordination degree index showed that the coordination among land functions was high in the south and low in the north, which was mainly controlled by ecological functions. The effects of natural and anthropogenic drivers on land functions showed nonlinear characteristics, and thresholds existed for some factors showing the abrupt change in influence. We concluded that our research provides reliable and detailed information about the interactions among land functions, which is essential for sustainable land use and territorial spatial planning.