WHAT THE EVIDENCE SAYS
Researchers analyzed 116,387 citizen-science bird records from 2022–2024 across Nanjing and compared land-sparing and land-sharing patterns at multiple spatial scales. Concentrated green space tended to support higher diversity, especially for resident birds where total green cover was below about 50%, while more distributed green share could favor migrants in greener landscapes and during non-breeding periods. Human footprint was a consistent predictor, and several sparing-versus-sharing contrasts were not statistically significant.
WHY IT MATTERS / OUR READ
Urban biodiversity design may not have one universal green-space geometry. Residents and migrants use the city differently, and the useful scale of planning may be neighborhood-sized rather than parcel-sized. That argues for network design based on movement and seasonal function, not only total acreage.
CAVEATS / UNCERTAINTY
Citizen-science records are uneven in observation effort and the study is observational. The reported threshold-like patterns should not be treated as a fixed 50% design standard, and effects may differ among cities with different climates, species pools and urban forms.
SOURCE
Landscape Ecology · Original evidence
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