Non-linear responses and critical thresholds of human well-being to ecosystem services across land-use intensities in urbanizing areas

Human well-being (HWB) cannot be sustained without ecosystem services (ESs). While many studies have explored the complex relationship between ESs and HWB, few have focused on their non-linear relationships and threshold effects, and how these vary under different land-use intensities. This study quantified and mapped ESs and HWB from 2000 to 2020 in the Xiamen-Zhangzhou-Quanzhou area in China. To examine how each ES contributed to HWB and their variation across land-use intensities, the random forest was employed. Restricted cubic splines were applied to identify non-linear relationships and critical thresholds, examining how these relationships changed with varying land-use intensity. The findings show that among different ESs, grain production had the greatest impact on HWB throughout the entire area, as well as in both areas with low and high land-use intensities. ESs and HWB had a significant variation of relationships, most of which displayed non-linear patterns and threshold effects. Many associations followed an inverted “U” shape, with a maximum threshold. The non-linear relationship between ESs and HWB differed across land-use intensities. It is manifest mostly from a significant nonlinear relationship in the low land-use intensity areas to a non-significant one in the high land-use intensity areas. HWB was less dependent on local ESs in areas with high land-use intensity than low land-use intensity, revealing a social-ecological system archetype of change. Critical threshold identification of how ESs and HWB interact can help guide social-ecological systems toward sustainable development.