Fragmentation typologies, trajectories, and path dependence in urban mangrove landscapes of Southeast Asia

In rapidly urbanizing coastal regions, mangrove ecosystems are increasingly fragmented by cumulative human and natural disturbances. Fragmentation is widely recognized as a dynamic process shaped by historical legacies. However, it is still most often assessed using snapshot-based measurements that obscure the spatiotemporal pathways through which fragmentation develops. As a result, it remains difficult to distinguish among transformation pathways and to determine how prior fragmentation states influence subsequent patch outcomes. This study aims to (1) characterize urban mangrove fragmentation as a set of distinct spatiotemporal change signatures using patch-level typologies; (2) identify dominant fragmentation pathways and their association with patch outcomes across diverse urban landscapes; and (3) examines how the history of fragmentation influences subsequent patch outcomes by quantifying whether earlier states provide information beyond the immediately preceding state. Mangrove fragmentation was analyzed across 21 Southeast Asian urban areas from 1996 to 2020 using patch-level landscape metrics derived from Global Mangrove Watch data. Fragmentation typologies were identified using a Random Forest classification approach and linked across time using a maximum-overlap tracking framework to reconstruct multi-step patch trajectories. Path dependence was evaluated within a closed cohort of baseline-traceable patch trajectories using an information-theoretic framework. Entropy reduction (ΔH) was used to measure how much earlier fragmentation states reduced uncertainty about later patch outcomes beyond the information provided by the immediately preceding state. Across urban areas, mangrove patches consistently became smaller, more edge-exposed, geometrically simpler, and more isolated, indicating widespread intensification of fragmentation. However, similar trends in aggregate metrics arose from different spatiotemporal transformation pathways. These differences were captured by four dominant fragmentation typologies—Nibbling, Clearing, Shattering, and Displacing—which varied across urban areas in both frequency and spatial extent. Fragmentation trajectories were highly uneven, with a small number of recurring pathways accounting for most observed sequences among baseline-traceable patch trajectories. Pathways dominated by Shattering and Clearing were consistently associated with higher probabilities of patch loss, indicating that specific sequences of spatiotemporal transformations are linked to degradation outcomes. Entropy-based results showed that earlier fragmentation states provided measurable, though limited, additional information about later patch outcomes (ΔH ≈ 0.11–0.16 bits), indicating weak-to-moderate but stable historical constraint. Findings from urban mangrove systems in Southeast Asia show that fragmentation unfolds through recurring sequences of spatiotemporal transformations that shape patch outcomes over time. Identifying fragmentation pathways provides a clearer basis for understanding landscape change and associated risks than snapshot metrics alone. Path dependence quantifies how much earlier states inform later outcomes, offering complementary insight into fragmentation dynamics. Together, the typology- and trajectory-based framework provides a transferable approach for diagnosing fragmentation pathways and identifying high-risk pathways in urban and other human-modified landscapes.