| With the continuous urbanization process,the land use types in the core development area of the Central Plains urban agglomeration have changed greatly.The accelerated urbanization process has negatively or positively affected vegetation growth and in turn affected various ecosystem service functions.Previous studies on the interaction between urbanization and ecosystem services have focused on national,provincial and city scales,but fewer studies have been conducted on urban agglomerations with uneven development.In this study,the core development area of the Central Plains urban agglomeration in China was used as the study area,and the study area was divided into old city,expansion area,suburban area and non-urban area,and three indicators such as population density,GDP density and urban expansion ratio were used to quantify the comprehensive urbanization process.Based on meteorological data and multi-source remote sensing data,the CASA model was used to estimate the Vegetation net primary productivity（NPP）of the study area for the past four decades,and the direct and indirect impacts of urbanization process on NPP were analyzed.An integrated assessment model of ecosystem services and trade-offs was used to assess water yield and soil conservation services,and a spatial correlation model was used to explore the interaction between urbanization and ecosystem services,and the trade-off/synergistic relationship between different ecosystem services.The main findings of this study are as follows:1.The core development area of the Central Plains urban agglomeration experienced a high rate of urbanization from 1980 to 2020,with an increase of 2,688 km2 of urban land area,and the increased urban land was mainly derived from arable land.In different regions,the urban land in the urban expansion area is mainly transferred from other land types,while the old urban area still maintains the urban land type.Different factors of urbanization show an increasing trend,among which the rapid increase of urban area,regional GDP and urban population.Spatial distribution shows that high values of population density,GDP density and urban expansion ratio are mainly distributed in urban areas,with the most concentrated spatial distribution of population density and urban expansion ratio mainly concentrated in urban expansion areas.2.the multi-year average value of NPP in the core development area of the Central Plains urban agglomeration was 544.20 g C m-2 a-1 from 1983 to 2019,and the multi-year change of NPP showed a decreasing trend.Among the different land use types,forest land and grassland have the highest NPP values,followed by arable land NPP values,and urban areas have the lowest NPP values.from 1991 to 2019,NPP in more than 80%of urban land is characterized by a significant decline,and the rate of decline of NPP in urban areas is greater than that in suburban and non-urban areas.In cities with different levels of development,the NPP of cities with high growth rates declined more in sprawling areas,while the NPP of cities with medium and low growth rates declined more in older urban areas.3.It was found that urbanization has direct and indirect impacts on NPP.The direct impact is the decrease of NPP due to the replacement of vegetation cover by urban land,and the indirect impact promotes the synthesis of NPP;the direct impact increases with the acceleration of urbanization,and the indirect impact has an overall increasing trend;the value of indirect impact is larger in urban areas than in suburban areas;temperature is the main climatic factor of indirect impact compared with precipitation,and the improvement of vegetation growth is greater in autumn and winter than in summer;The correlation between indirect impacts and temperature is greater in urban areas than in suburban areas.4.The multi-year changes in NPP,water yield and soil conservation all showed a decreasing trend,and there were regional differences in the trends.Among them,the decreasing trend of NPP is closely related to the decrease of vegetation cover area.The multi-year changes in water yield and soil conservation services also showed a decreasing trend.In different cities,significant spatial heterogeneity was observed among the hotspots of various ecosystem services;NPP hotspots were mainly concentrated in areas with high vegetation cover such as woodlands（Luoyang and Jincheng）;water yield hotspots were mainly concentrated in the southeastern plains of the region（Luohe,Zhoukou and Bozhou）,and hotspots also appeared in and around Zhengzhou City by 2019;soil conservation hotspots were mainly in woodlands in the north and southwest of the study area;In addition to the impact of urban land expansion,the changes in ecosystem services may be related to the environmental protection policies of different administrative regions.5.water yield was positively correlated with different factors of urbanization,while NPP and soil conservation services were negatively correlated with different factors of urbanization;the spatial role of urbanization in relation to ecosystem services depended on the type of service selected,and the degree of development of urban agglomeration.The ecosystem service trade-off synergistic relationships are that there is a synergistic relationship between NPP and soil conservation services,and a trade-off relationship between NPP and water yield,water yield and soil conservation services.from 2000 to 2019,the correlation between NPP and soil conservation services increased,while the correlation between NPP and water yield,water yield and soil conservation services did not change greatly.The reason for the change in the synergistic relationship of ecosystem service trade-offs in local areas may be related to changes in land use or climatic factors.This study is important for understanding the urbanization process in the core development area of the Central Plains urban agglomeration,identifying the impact of urbanization on regional vegetation growth,as well as exploring the spatial interaction between urbanization and ecosystem services,judging the trade-off synergistic relationship between different ecosystem services,and supporting urban agglomeration greening planning and building a sustainable and resilient urban agglomeration,providing a reference for the high-quality spatial development of the urban agglomeration. |
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