Wei Liu

In the urbanization development trend, constructing inter-provincial metropolitan areas has gradually become an important pathway for China to implement its new urbanization strategy. Economic development in metropolitan areas inevitably leads to ecological degradation and fragmentation, threatening biodiversity. A reasonable assessment and optimization of the ecological network structure of inter-provincial metropolitan areas can effectively improve the stability of regional ecosystems and contribute to the sustainable development of urban and rural environments. In this study, we optimized the identification of ecological sources at the metropolitan area scale by constructing the ‘MIE’ model combined with the threshold analysis method, identified the core ecological sources in the Xuzhou Metropolitan Area, a typical cross-provincial metropolitan area in China, and then extracted the ecological corridors by using the Linkage Mapper tool based on this method. The spatiotemporal patterns and components of the ecological network of the Xuzhou metropolitan area from 1990 to 2020 were assessed, and an optimization analysis was performed based on the current ecological network. The results show that urban expansion has caused a decentralized layout of the ecological space in the study area across the provincial metropolitan area, with an uneven distribution of ecological sources and the development of ecological corridors in an east-dense and west-sparse pattern in 30 years. Increased interference by human activities has decreased the landscape dominance of the regional ecological resources and overall fragmentation of the habitats. The number of ecological corridors decreased, the average length of ecological corridors increased, the difficulty of biological flow increased, the connectivity of the ecological network structure decreased, and accessibility between source areas decreased. The α, β, and γ indices of the regional ecological network increased by 0.16, 0.46, and 0.1, respectively, after restoring important ecological sources and corridors. This study provides a framework for ecological network assessment and optimization in cross-provincial metropolitan areas, which is of great significance for studying metropolitan areas at similar stages of development.

The construction of refuge spaces in rapidly urbanizing historic cities is a challenging task owing to their complex urban form, unique urban fabric, and historic preservation requirements. Refuge green space (RGS) is a green space that can serve as an emergency shelter in cities, providing a flexible means to increase the emergency shelter capacity for rapidly urbanized historic cities. After major earthquakes, spatial accessibility to GRSs is a critical planning strategy for disaster prevention and emergency response in historic cities. To match the RGS planning with the emergency service demand, we must examine the spatial disparity in access to existing RGSs. In this study, the urban area of Nanjing was selected as the target region to analyze the spatial disparity in access to RGSs using the Gaussian two-step floating catchment area method at four evacuation times (10, 20, 30, and 60 min). The results showed that the spatial accessibility exhibited clustering characteristics, where high-accessibility spaces were mainly distributed in the northern and southern regions of Nanjing. The increase in the evacuation time improved accessibility to RGSs, but the existing RGSs still could not sufficiently satisfy the emergency shelter needs of citizens. Based on the bivariate local Moran’s I analysis of the RGS accessibility and population density, the spatial mismatch regions were dominant in the center of the urban area. These findings not only are expected to assist emergency planners by improving their strategic plans for emergency shelter investment in Nanjing and their ability to respond to catastrophic earthquakes, but also provide a strong reference for the construction of a safe environment in other rapidly developing historic cities that face earthquake threats.

Clustered urban development has caused increasing fragmentation and islanding of regional ecological spaces. Creating a green infrastructure network (GIN) is a practical method of ensuring regional ecological security. This study proposed a method of GIN identification at the regional scale based on the Nanjing Metropolitan Area as an example. In this method, green hubs were identified using morphological spatial pattern analysis and connectivity indexes, green corridors were simulated based on the least-cost path model, and key optimization nodes were identified using circuit theory. The results indicated that green hubs covered an area of 5042.07 km², of which, 15.40% were cross-border, and the potential corridors were distributed in a network, with the key ecological nodes primarily narrowly situated. By comparing the hubs with the statutory green space protection area and the urban ecological control line, the identification results were more than 70% accurate, showing that the results were valid and reliable. This method not only made the identification of regional GIN more practical and replicable but also further identified key areas that need priority protection. This study provides a method for constructing regional GIN and serves as a strong guide for ecological and development planning of other urban clustered areas.