Spatiotemporal dynamics of mangrove ecosystems in the Mai Po Nature Reserve Ramsar site: Drivers, challenges, and implications

The global decline of mangrove ecosystems underscores the imperative for effective conservation and restoration strategies, particularly through the designation and management of protected areas. Understanding mangrove spatiotemporal dynamics within these nature reserves is critical for informing sustainable conservation efforts. This study utilizes multi-temporal remote sensing data coupled with machine learning techniques to investigate the spatiotemporal changes in mangrove coverage within the Mai Po Nature Reserve, Hong Kong—a Ramsar site since 1984 and one of the earliest mangrove nature reserves globally. Over the past three decades (1986–2023), the reserve has experienced a notable expansion in mangrove vegetation, with an average growth rate of 5.7 ha per year. The shoreline exhibits a distinct “M”-shaped seaward expansion, with rapid progradation rates of 20.81 m per year in the northern region and 11.10 m per year in the southern region, while the central area shows a slower progression at 2.43 m per year. A transition from exponential to linear growth post-2005 correlates with decreased sediment supply from the Shenzhen River and the systematic removal of pioneer mangrove seedlings since 2006. Weak wave energy and tidal forces have also facilitated the observed expansion. Projections suggest that, under rising sea levels and without human intervention, the Mai Po mangroves could fully occupy the intertidal zone within approximately 219.5 years. Results indicate that the current conservation strategy has facilitated vegetation expansion; however, this has occurred at the expense of the loss of mudflat areas. This trade-off raises important conservation questions regarding how to effectively balance the management and regulation of estuarine mangroves to ensure both ecological preservation and habitat integrity. This study demonstrates substantial natural expansion under Ramsar protection, offering critical insights into the mechanisms governing mangrove growth and informing global conservation and management practices for these vital ecosystems.