Spatial spillovers and nonlinear effects of urban green space on population aging in China

China is undergoing the world's most rapid demographic transition, with the pressure of population aging becoming increasingly prominent. As a core component of green infrastructure, urban green spaces are gaining attention for their role in alleviating the pressures of aging. However, existing research has primarily focused on the localized benefits of urban green spaces, with insufficient exploration of their spatial effects. This study employs panel data from 300 prefecture-level cities in China spanning 2001-2023, utilizing spatial Durbin models and threshold regression models to systematically examine the spatial effects of urban green spaces on aging. It further analyzes their significance in regional collaborative governance. Findings reveal that aging exhibits distinct spatial clustering patterns. Urban green spaces not only alleviate local aging pressures by improving environmental quality, promoting physical activity, and enhancing public health, but also generate significant spatial spillover effects that positively influence aging processes in surrounding areas. Threshold analysis further indicates that the impact of urban green spaces on aging exhibits nonlinear characteristics, with their positive effects significantly intensifying once green space coverage reaches a certain critical threshold. This study emphasizes that in today's era of frequent population mobility and deepening regional integration, examining green space policies solely from an intra-urban perspective is insufficient to address aging challenges across administrative boundaries. Recognizing and prioritizing the spatial spillover effects of urban green spaces not only facilitates the establishment of collaborative aging governance systems across cities but also provides theoretical foundations and policy insights for advancing the Healthy China 2030 strategy and achieving balanced regional green development.