Abstract
<title>Abstract</title> <p>Building-integrated greenery (BIG), implemented through green roofs and walls, can restructure urban ecological networks by enhancing habitat continuity and reducing fragmentation. However, quantifying these benefits across the city remains challenging due to complex interactions between urban morphology and landscape ecology. This study simulates incremental BIG adoption across existing buildings in Sydney, Australia, to evaluate how progressive roof and wall greening influence spatial structure and functional connectivity for insect pollinators and woodland birds. Using open-source spatial datasets and geocomputational modelling, we quantified habitat fragmentation, cluster configuration, and ecological connectivity across scenarios from 0% to 100% BIG coverage. We identified the inflection points at which ecological benefits accelerate or decelerate using landscape metrics and network analysis. We found that BIG catalyses non-linear ecological transitions with threshold-dependent dynamics across four phases: transition, reconnection, consolidation, and saturation. A critical inflection point emerged at 20% BIG coverage, where connectivity metrics shift from negative to positive rates of change. Between 20–40% coverage, configuration metrics showed sustained acceleration as critical patches proliferate across the landscape. Betweenness centrality indicated that connectivity emerged from the collective contribution of moderately important stepping-stone patches rather than dependence on individual bottleneck nodes. There were diminishing returns in connectivity from additional greening beyond 70% coverage. Green walls outperformed green roofs in early connectivity for insect movement, retaining broader spatial distributions of important patches at equivalent early coverage levels. These findings indicate that effective strategic placement of BIG matters in lower coverage of up to 40%. Cross-jurisdictional governance frameworks aligned with landscape-scale ecological processes would be more effective at improving ecological connections in urban environments than the existing emphasis on individual buildings or administrative boundaries.</p>