When does rural population decline improve ecological quality? Evidence from population-density thresholds and spatial heterogeneity across Chinese counties

While a reduction in rural population density is commonly believed to alleviate human-land pressure and enhance ecological quality, this relationship may be far more complex when nonlinear dynamics are taken into account. Focusing on rural China, this study examines, whether the ecological effects of declining population density vary across different population density levels by employing county-level data from 2000 to 2020. The results show that ecological quality has generally improved across rural China, while pressures persist in developed and densely populated areas. More importantly, a clear double-threshold in rural population density is identified: one is an “Effect Intensification Threshold”, below which the ecological benefits of rural depopulation accelerate markedly, and an “Effect Reversal Threshold”, beyond which continued population loss reverses these benefits and leads to ecological degradation. Furthermore, regional disparities are pronounced, with ecological carrying capacities corresponding to differentiated threshold points: the Eastern region exhibits higher threshold levels, whereas the central and western regions generally follow the national pattern. Overall, this study advances a dynamic framework for understanding human-land interactions in depopulating rural systems and provides critical evidence for designing spatially tailored ecological policies.