Do Urban Decentralization Policies Affect the Green Space? A Case Study of Beijing

To tackle the challenges of “urban diseases” brought about by excessive urbanization, numerous cities worldwide have implemented decentralization policies. Unlike previous socioeconomic-focused studies, this research evaluates the 2015 policies aimed to relieve Beijing of functions non-essential to its role as the capital (RBNE), analyzing its differential impacts on green space (GS) and underlying mechanisms. Using street-level panel data (2009-2020) and combining difference-in-differences (DID) and Sobel tests, the study reveals: (1) RBNE significantly improved GS in the central urban area (CUA) but caused negative effects in urban development (UDA) and ecological conservation areas (ECA). (2) The heterogeneity of functions and institutions has led to different outcomes: In CUA, Xicheng District has shown the largest increase in green space, Dongcheng District has shown a smaller increase in green space, while in Changping District of UDA, the phenomenon of “reverse centralization” has occurred. (3) Population density thresholds influenced spatial patterns, with GS improvements concentrated in CUA streets (≥3,000 people/km²) and declines in lower-density UDA areas. (4) Mechanism analysis identified land cover changes and tertiary industry development as primary drivers of GS improvement in CUA, while population factors showed limited mediation. Night-time light intensity generally masked policy effects, suggesting complex human activity interactions. The empirical results indicate that establishing a differentiated regulation mechanism that aligns with urban functional zoning will contribute to solving the difficulties in maintaining and increasing green space in different urban regions. This achievement provides an important reference paradigm for global megacities to balance the optimization of functional layout and the sustainable development of the ecosystem in the design of decentralization policies.