Variation in ecosystem services across an urbanization gradient: A study of terrestrial carbon stocks from Changzhou, China

Ecosystem services in urban areas are regarded as multiple environmental benefits fostered by urban-rural landscapes. A wide range of ecosystem services have been largely affected by land use and cover change in urban areas, leading to significant variation of ecosystem services, such as terrestrial carbon stocks across a gradient of urbanization. Urban areas are critical for terrestrial carbon dynamics owing to both considerable amount of biomass and soil carbon stored in cities and significant losses in carbon stocks from urban land use and cover change. We used Changzhou, a typical fast-growing city in China, as a case study, and estimated biomass and soil carbon stored in land covers using the InVEST model. We also quantified gradient changes in terrestrial carbon stocks in response to urban land use and cover change along two sample transects as a function of distance from the urban center. We found that carbon densities decreased with increasing intensity of urban development. Gradient transect analyses revealed an overall trend of increasing carbon stocks from the urban center to peri-urban areas as a direct result of land use and cover change driven by policy-oriented urban planning, which led to both infilling of empty areas within the urban center and sprawling of urban land toward peri-urban areas. As recent growth trends continue, the expansion of urban land markedly decreased areas previously dominated by green open spaces, making urban land use and cover change and losses in carbon stocks an increasingly important component of regional carbon dynamics. We proposed measures to mitigate these negative effects of urbanization on carbon stocks both for densely built-up areas and for rapidly urbanizing peri-urban areas.