Li and colleagues bring evidential discipline to the rapidly expanding field of urban nature-based solutions. Their systematic review analyses 185 cases across 87 cities in 33 countries and finds that most reported NbS interventions improve biodiversity relative to non-NbS situations. Yet the more important finding is epistemic incompleteness: evidence is concentrated in particular taxa, intervention types and familiar indicators, while a majority of cases lack baseline measurements. Multifunctionality is therefore easier to assert than to demonstrate. The paper’s methodological force lies in examining not only outcomes but the architecture of evaluation itself—what is measured, compared and omitted. It bridges urban ecology with evidence governance by showing that biodiversity-positive policy requires comparable baselines, appropriate indicators and transparent evaluative frames. The city becomes a distributed experiment whose capacity to learn depends on the quality of its measurements.
