A reference-based ecosystem health indicator framework to disentangle population impacts under multi-factor environmental change

Ecosystem health provides an integrative measure of ecological change under increasing human pressure, yet quantitatively characterizing the role of population dynamics remains challenging at fine spatial scales. This study investigates spatiotemporal variations in ecosystem health and their association with population change at the township level in Chongqing, China, over the period 2000–2023. Ecosystem health was assessed using multi-source remote sensing data and census statistics within a Pressure–State–Response (PSR) framework, and township population dynamics were analyzed using spatial statistical and regression approaches. Results indicate that the ecosystem health index (EHI) exhibited a pronounced U-shaped trajectory over the past 24 years, shifting from degradation to gradual restoration. Spatially, ecosystem health levels were consistently higher in northeastern and southeastern Chongqing than in western regions. Township populations displayed a polycentric spatial pattern, with strong concentration in the main urban area and its surrounding townships. Population pressure was predominantly associated with ecosystem health degradation. Notably, although approximately 58% of townships remained below their ecological population carrying capacity, population dynamics in these areas were still linked to measurable declines in ecosystem health. After isolating background environmental influences using long-term sub-capacity townships as reference areas, a significant and stable negative relationship was identified between population change and ecosystem health across two independent periods. These results provide robust empirical evidence that population redistribution and concentration exert sustained negative effects on ecosystem health at the township scale, even in the absence of population overshoot, highlighting the sensitivity of fragile mountainous ecosystems to demographic change under rapid urbanization. • Township-scale ecosystem health follows a U-shaped degradation–recovery trajectory. • A reference-based framework isolates population effects on ecosystem health. • Population pressure forms stable spatial clusters under urbanization. • Population change shows a robust negative linear effect on ecosystem health.