Tracking the decadal dynamics of native and exotic mangroves in an urban coastal wetland: an integrated OBIA-CNN approach
摘要
Fine-scale, species-level monitoring of mangrove dynamics is critical yet challenging, especially in urban coastal wetlands where native and exotic species interact. To address this, we developed an integrated remote sensing workflow that combines Object-Based Image Analysis (OBIA) with a Convolutional Neural Network (CNN). This OBIA-CNN approach was applied to high-resolution WorldView-3 imagery to map decadal changes (2015–2025) in mangrove cover and species composition for five key species in Shenzhen’s Futian Mangrove Nature Reserve. Our results revealed a substantial 43% expansion in total mangrove area (from 96.65 to 137.71 ha). However, species-level analysis uncovered strikingly divergent trajectories: the exotic Sonneratia species experienced initial rapid expansion, followed by a sharp decline primarily driven by targeted management interventions (i.e., manual removal of exotic trees), with natural succession playing only a secondary role. In contrast, the native Kandelia obovata exhibited steady expansion and increased landscape consolidation, ultimately re-establishing dominance. Analysis of landscape metrics and species replacement pathways highlighted the competitive interplay between species, identifying mangrove-mudflat edges as critical hotspots of change. During its expansion phase, the exotic Sonneratia competitively suppressed native mangrove growth through canopy shading; however, the subsequent replacement by K. obovata was facilitated by management-driven removal rather than natural competitive displacement. This study provides not only a robust and transferable methodology for fine-scale, long-term mangrove monitoring but also critical insights for managing exotic species and conserving biodiversity in urban coastal wetlands.