Quantifying the indirect effects of urbanization on urban vegetation carbon uptake in the megacity of Shanghai, China

Urbanization causes the expansion of urban land and changes to urban environments, both of which have significant impacts on the carbon uptake of urban vegetation. Although previous studies have proposed that the impact of the changes in the environmental conditions of vegetation carbon uptake by urban expansion are generally indirect, the processes of this impact are still unclear. In this study, we quantified the indirect effects of urbanization on urban vegetation carbon uptake for unchanged vegetation areas. We extracted unchanged vegetation areas based on multisource remote sensing data from the Google Earth Engine cloud computing platform. The influence of urbanization on vegetation carbon uptake and urban environmental factors in 2004, 2010, and 2016 along with the urban–rural gradient was calculated. In addition, we investigated the relative contribution of urban environmental factors to vegetation carbon uptake to study the relationship between them using a boosted regression tree method. The results showed that urbanization promoted vegetation carbon uptake, which varied with different years in Shanghai. Besides, the promoting effect of urbanization on the carbon uptake of vegetation was mainly due to the increase in temperature and the fragmentation of vegetation landscape patterns in Shanghai. The changes of soil moisture and radiation had little effect on the vegetation carbon uptake. Among the influencing factors, the relative contribution of the vegetation landscape pattern to vegetation carbon uptake was about 85%. Considering the crucial role of landscape patterns in the carbon uptake of vegetation, urban managers should consider reducing the negative influence of urbanization on vegetation through landscape design, which will further promote the sustainable development of urban ecology.