The Spatiotemporal Variation Characteristics And Driving Factors Of Gross Primary Productivity Of Urban Vegetation In Shanghai

Climate change and urbanization are the two main driving forces that can change the growth process of vegetation in the urban environment.The first is that climate-related factors,such as temperature and precipitation,provide the necessary conditions for vegetation to grow.Meanwhile,it will be accompanied by the expansion of impervious surfaces,which will reduce the growth space of urban vegetation.However,along with the advancement of the urbanization process,the internal environment of the city has also changed,which may have a negative impact on the growth of vegetation,and may also promote the growth of vegetation.At present,the research on how climate change and urbanization drive the growth of urban vegetation still has certain limitations.Therefore,clarifying the temporal and spatial trends of urban vegetation gross primary productivity and discussing its different effects on urban vegetation gross primary productivity from three aspects of climate change,urban expansion,and urban environmental changes are of great significance to the development of urban green space planning and management.Shanghai has experienced rapid urbanization and industrialization.At the same time,Shanghai has retained areas that are relatively less affected by urbanization,such as Chongming.The simultaneous existence of urban and rural areas makes Shanghai suitable for assessing the impact of climate change and urbanization on vegetation.Based on the Google Earth Engine(GEE)cloud computing platform and multi-source remote sensing image,this research studies the spatiotemporal characteristics and driving factors of the gross primary production(GPP)of Shanghai's vegetation.The following conclusions are drawn after research:(1)From the perspective of time scale,Shanghai's GPP showed a significant decrease during 2004-2016(p<0.05).From a spatial point of view,GPP in most areas of Shanghai downtown showed a significant increase(p<0.05),while GPP in most areas outside the center of Shanghai showed a significant decrease(p<0.05).(2)Comparatively speaking,Chongming district can eliminate the impact of urbanization on the GPP caused by environmental changes.Therefore,the Chongming district is used as the study area to study the impact of climate change on Shanghai's GPP.Meanwhile,the temperature and precipitation data characterize the urban climate.During 2004-2016,the precipitation in Chongming district increased significantly(p<0.05),while the temperature did not change significantly during this period,and the changing trend of GPP in Chongming district responded more significantly to temperature than to precipitation.(3)Impervious surface coverage(ISC)changes characterize urban expansion.From a time scale,ISC showed an overall upward trend from 2004 to 2016.From a spatial perspective,the significant increase in ISC is mainly concentrated in the periphery of Shanghai(p<0.05).Based on impervious surface coverage and GPP data,the direct impact of impervious surface expansion on vegetation is calculated,and it is concluded that the urban land expansion directly caused GPP loss of 135.85 g-C m-2 in Shanghai from 2004 to 2016.(4)Based on the urban-rural gradient method to compare and observe the response of vegetation to the urban environment,it is concluded that the changes in the urban environment caused by urbanization have a promoting effect on the growth of vegetation,and the promotion effect of urbanization on vegetation varies with the development stage of urbanization and the different urban ecological environment management policy.(5)The changes in the urban environment are characterized by changes in surface temperature,soil moisture,photosynthetically active radiation,and vegetation landscape connectivity.The change in the urban vegetation landscape connectivity is the main reason for promoting the growth of urban vegetation.This may be due to the low connectivity of urban vegetation compared with the highly connected landscape pattern of rural vegetation.Resource availability is higher,and at the same time,places with low vegetation connectivity are often areas where human vegetation management is strengthened.In addition,the increase in urban temperature caused by urbanization also promotes the growth of vegetation near the center of Shanghai,while changes in soil moisture and radiation have less impact on vegetation growth.Although the fragmentation of vegetation landscape promotes the carbon sequestration capacity of vegetation,the direct loss of vegetation fragmentation is still greater than its promotion effect.Therefore,the development and planning of green landscapes in cities should consider the balance between land use and ecosystem services in cities to maximize the benefits brought by vegetation.