Abstract
Urbanization has destroyed and fragmented large amounts of natural habitats, resulting in serious consequences for urban ecosystems over past decades, especially in the rapidly urbanizing areas of developing countries. The Yangtze River Delta Urban Agglomeration, which has experienced the fastest socioeconomic development in China, was selected as the study area. To explore the relationship between urbanization and vegetation dynamics at the agglomeration scale, the spatiotemporal characteristics of urban expansion and vegetation variation of the study area were evaluated by landscape spatial analysis, regression analysis, and trend analysis. The results show that the urbanization level of the study area exhibited a continuous upward trend, with Shanghai as the regional core city, and the level of urbanization gradually decreased from the center towards the periphery of the urban agglomeration. The overall urban expansion presented obvious landscape spatial heterogeneity characteristics and the emergence of new cities and towns enhanced landscape connectedness and created a more aggregated urban agglomeration. Noticeable spatiotemporal differences of vegetation variation were observed from 2004 to 2013. Areas with relatively low vegetation coverage showed a steady growth trend, while those with higher vegetation coverage reported a significant decreasing trend. The spatial heterogeneity analysis of the vegetation trend demonstrated that vegetation degradation was a dominant and inevitable process across the study area. However, some parts of the urban sprawl area, especially at the periphery of the metropolis, may experience a greening trend rather than a browning trend, indicating that urbanization does not necessarily lead to large-scale vegetation degradation. Although urbanization poses a negative impact on vegetation and physical environments, urbanization has not yet reduced a large area of vegetation at the regional level.
Highlights
Urbanization is usually accompanied by land use change and urban expansion, and is among the most irreversible human impacts on the global biosphere [1]
To explore the relationship between NTL intensity and the urbanization level of the Yangtze River Delta Urban Agglomeration (YRDUA), the average nighttime light intensity index (ALI) and composite urbanization index were defined in this study
We investigated the urbanization level, urban expansion characteristics, and its effects on the vegetation variation in the YRDUA from DMSP/OLS NTL and Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) images over the past decade
Summary
Urbanization is usually accompanied by land use change and urban expansion, and is among the most irreversible human impacts on the global biosphere [1]. The transformation of natural landscape exerts a predominant influence on the local climate and environment by modifying the surface roughness, albedo and evapotranspiration and increasing the aerosols, exacerbating the urban heat island effect and altering the precipitation patterns at a regional scale [2,3]. Studies on broad-scale urbanization and its ecological effects are becoming increasingly important for natural resource management and regional planning. Many studies have been conducted to quantitatively monitor urban landscape dynamics and estimate urban ecosystem pressure to understand the spatio-temporal characteristics and ecological effects of urbanization. The change in urban landscape pattern is one of the most conspicuous aspects of urbanization, and it poses a variety of negative influences on the physical environment and ecosystems
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