Assessing the differences in net primary productivity between pre- and post-urban land development in China

Urban land development substantially alters the terrestrial carbon cycle, particularly the net primary productivity (NPP), from local to global scales. However, limited attempts have been undertaken to elucidate the differences in NPP between pre- and post-urban land development in China. In this paper, the terrestrial NPP after urbanization in China was assessed by using the Carnegie-Ames-Stanford approach (CASA), toward which a calibration was conducted for adapting this model on the fine-scale application. In addition, a method of neighborhood proxy was applied to acquire the NPP in the absence of urban land development, assuming that non-urban lands can represent their nearby urban lands before they were transformed. Our analyses indicate that urban land development had overall negative effects on terrestrial NPP. They reduced the NPP at an accelerating rate of 0.31×10^-3PgCyear^-1, approximately 5.88% of the annual reduction during the period of 2000-2006 in China. Furthermore, these effects of NPP variations exhibited obvious differences in the amounts and spatial distributions. However, the NPP showed a slight increase around some regions that experienced rapid urbanization, as well as the arid regions in northwest China. These were probably caused by the effects of Urban Heat Island (UHI) and Urban Rain Island (URI), an introduction of faster growing exotics, various resource augmentations and so on.