Drought and fragmentation shape successional trajectories of isolated urban forests in South Korea

Managing urban forest successional trajectories is essential for sustainable and cost-effective ecological restoration. However, successional pathways in South Korea's urban forests are frequently disrupted by environmental and anthropogenic pressures, threatening their long-term sustainability. This study examined successional pathways and their environmental determinants in isolated urban forest patches across seven metropolitan cities. Structural equation modeling was used to assess relationships among environmental variables, canopy structure, and successional pathways, and key drivers were identified using Random Forest analysis. Overall, 83.2% of plots exhibited progressive succession, transitioning from early-successional invasive alien or introduced species toward mid- to late-successional native communities. In contrast, 16.8% of plots underwent retrogressive succession, characterized by shifts from Quercus-dominated stands toward stress-tolerant, urban-adapted species associated with earlier successional or degraded conditions. Drought severity and forest patch size emerged as the primary determinants of successional pathways. These findings demonstrate how climatic stress and spatial constraints linked to fragmentation shape UF dynamics at a regional scale and provide insights for targeted restoration strategies that promote progressive succession and enhance the long-term sustainability of urban forests.