Impact of Urbanization on the Total Primary Productivity of Terrestrial Ecosystems in Nanjing Area

Based on multisource remote sensing data and downscaled vegetation productivity data, the spatiotemporal dynamics of urban expansion, its direct and indirect effects on Gross Primary Productivity (GPP) in Nanjing from 2000 to 2020 are investigated. Results reveal a considerable expansion of the urban area in Nanjing from 2000 to 2020, causing the doubling of the impervious surface from 620.31 km² in 2000 to 1245.66 km² in 2020. Due to the increase in urbanization intensity, the direct effect of land cover change caused a decrease of −345.98 g(C) m^－2 a^－1 in the GPP of Nanjing urban area, whereas the indirect effect of regional climate change and urbanization caused an increase of 298.67 g(C) m^－2 a^－1 in the GPP of Nanjing urban area, which offsets 86.33% of the direct effect. The increasing trend and contribution rate of indirect influences in urban areas exceed those in suburban areas, indicating that the urban environment encourages residual vegetation growth. In terms of the continuous expansion of major cities worldwide, characterizing and understanding the effects of urban expansion on vegetation productivity hold considerable practical significance and reference value in addressing global change challenges and advancing the construction of ecologically civilized cities.