Urbanization-induced impacts on mangroves at multiple scales

Abstract

Mangroves are trees and shrubs that grow in coastal intertidal zones of tropical and subtropical regions with invaluable ecosystem service. Unfortunately, mangroves have decreased significantly over the past half a century due to a range of pressures stemming from natural and anthropogenic forces. Among those, urbanization stands out as a prominent human activity that has been increasing and intensifying. Previous studies have been limited to a single perspective of land urbanization. However, urbanization impacts encompass a wide range of anthropogenic activities that are interrelated and driven by the urbanization dynamic, leading to underestimation or overestimation of urbanization impacts on mangroves. This thesis aims to explore how urbanization affects mangrove ecosystems from multiple scales. To understand urbanization and mangrove systems, the thesis first presents in-depth explorations of each system individually. For the urbanization system, the development of effective population mapping based on both land urbanization and demographics transcends a solely land-based perspective. For the mangrove system, the employment of long-term, annual mangrove cover datasets enables exploration of the spatial and temporal evolution of mangrove gain and loss hotspots. This expands the spatially explicit understanding of mangrove transition with high temporal resolution over a long period. The study examines the impacts of urbanization on mangroves from the dimensions of inter-system and multi-system. Firstly, at the inter-system scale in China, the thesis analyzes the relationship between the urbanization system and the mangrove system as standalone entities. It was found that the impact of urbanization on the spatial extent of mangrove forests weakened gradually beyond nature reserves during 1973-2015. The conservation policies in nature reserves have made significant contributions to mangrove conservation in China. Secondly, at the inter-system scale in Southeast Asia, it evaluates the coupling dynamics between urbanization and mangroves as an integrated, coupled system. A large proportion of grids demonstrated an uncoupling phenomenon between urbanization and mangrove ecosystems, indicating a limited interaction between the urbanization process and the mangrove environment. While strong coupling relationship was significantly observed in the southern regions of the Philippines, exhibiting a high level of interconnectivity between urbanization and mangrove ecosystem. Thirdly, at the multi-system scale in global coasts, the impacts of urbanization on mangroves worldwide are analyzed, including the indirect effects mediated by climate, considering the interactions among the urbanization, climate, and mangrove systems. Urbanization and climate had positive impacts on mangrove growth and carbon stock in some regions during 1996-2020, which is different from the general belief of adverse impacts from previous research. Mangroves in subtropical/temperate climate zones experienced more positive impacts from urbanization which improves the local climate conditions for mangrove growth. By examining the spatial-temporal patterns of urbanization and changes in mangroves, along with the underlying mechanisms of impact, this research can guide the development of evidence-based policies and integrated management strategies. The interaction between urbanization and mangroves can help prioritize urban space planning and mangrove restoration efforts. This offers significant policy insights into achieving coastal sustainability and balancing urban development with coastal conservation, tailored to local conditions.