| Urbanization is the most typical feature of human society since the 20th century.During the process of urbanization,a large amount of greenhouse gases such as carbon dioxide was released into atmosphere,resulting global climate change.Arguably more than 80%of carbon dioxide emissions originate from urban areas.Urbanization dramatically altered carbon cycle in the terrestrial ecosystems.As the important component of terrestrial carbon cycle,net primary productivity?NPP?not only reflects the net productivity of vegetation under natural conditions,but also indicates the impact of human activities on carbon cycle in the terrestrial ecosystems.However,urban ecosystem is more complex than natural ecosystem and large uncertainty exists in urban carbon cycle.At present,there are few studies focusing on NPP in rapidly urbanized areas,and the effects of urbanization factors such as economic development,population growth and urban sprawl on NPP are still unclear.Therefore,it is very important to study the spatial and temporal pattern of NPP in rapid urbanization areas for understanding the interaction between human activities and ecosystems and designing sustainable region development planning.The core area of Yangtze River Delta comprises Shanghai,southern Jiangsu province?Nanjing,Suzhou,Wuxi,Changzhou,Zhenjiang,Yangzhou,Taizhou?,and northern Zhejiang province?Hangzhou,Ningbo,Huzhou,Jiaxing,Shaoxing,Zhoushan,Taizhou?.In this study,the spatial and temporal patterns of NPP in the core area of the Yangtze River Delta during the period of 2000-2016 were estimated using CASA model.Based on meteorological data and economic census data,the effects of climate factors and urbanization on NPP were analyzed.The main conclusions are as followings:?1?The NPP in the core area of the Yangtze River Delta during 2000-2016 showed an“N”type trend.It increased firstly during 2000-2004,then decreased from 2005 to2011,and then increased from 2012 to 2016,which was consistent with that in built-up areas and non-built-up areas.The interannual variation of NPP was different among the16 cities.The average NPP in the Yangtze River Delta was estimated to be 419.331gC·m-2·yr-1.High value occurred in the south?Taizhou,Hangzhou,Shaoxing,Zhoushan,Ningbo,Huzhou?and the north?Taizhou,Nantong,Nanjing,Zhenjiang,Yangzhou?,and low value occurred in the central area?Shanghai,Suzhou,Wuxi,Changzhou,Jiaxing?.The NPP in built-up areas was significantly lower than that in non-built areas,and there was also large heterogeneity between cities and within cities.?2?Meteorological factors?temperature,precipitation and solar radiation?affected the spatio-temporal pattern of NPP.The extreme climate events had a significant impact on the interannual variation of NPP.Moderate moisture,heat and light conditions were beneficial to increase NPP.The influence of precipitation and solar radiation on the distribution of NPP was greater than that of temperature.?3?Urbanization factors?GDP per area,proportion of urban population and proportion of built-up area?also affected the spatio-temporal pattern of NPP significantly.During the rapid development of urbanization,the GDP per capita,the proportion of urban population,and the proportion of built-up area had a negative impact on NPP.Low NPP occurred in cities with rapid economic growth.Urbanization might have a positive influence on NPP in the later stage of urbanization,under the influence of industrial restructuring,land intensive use,scientific urban planning,environmental protection policies and landscape greening projects.High NPP exited in cities with high urbanization level and urban landscaping level. |
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