Spatiotemporal Changes In Ecosystem Services Along A Urban-Rural-Natural Gradient

Urban areas are the areas that are most strongly affected by human activities,which presents many challenges to the ecosystem and human well-being.Ecosystem services(ES)are a comprehensive indicator to measure the ecological effects of urbanization.To effectively identify and evaluate the impact of urbanization on ES,the spatial-temporal pattern of ES should be considered.The objective of this paper is to explore the impact of urbanization on ecosystem services along urban-rural-natural gradients.In this paper,the urban-rural-natural gradient of Xi'an is constructed based on the impervious ground data of urban area.Xi'an is divided into four areas: urban core area,urban expansion area,rural area and ecological protection area.The spatial-temporal distribution and change of different gradients(water yield,water purification,soil conservation,carbon sequestration,food supply)and comprehensive ecosystem services were evaluated by invest model.We measure the level of urbanization from three perspectives: population urbanization,Economic Urbanization and landscape urbanization,and then analyze the relationship between urbanization and ecosystem services through correlation analysis,spatial autocorrelation and other methods.The results are as follows:(1)From the center of the city to the periphery of Xi'an City,the level of population,economy and landscape urbanization gradually decreased;from 2000 to 2015,the population,economic and landscape urbanization in most areas showed an increasing trend,mainly concentrated in the urban expansion area and the northern Xixian new area.(2)There was an obvious spatial heterogeneity in the distribution of ES.The ecological conservation area is the hot spot of ES supply,and the low value is mostly distributed in the urban core area.The comprehensive ecosystem services in the urban extended area that has undergone the greatest change between 2000 and 2015,and the rates of change in the ecological conservation area are the smallest.(3)We use correlation analysis and local autocorrelation to study the aggregation process of trade-off / collaboration between different ecosystem services.There are obvious trade-offs between grain production and water yield,soil conservation,n output service,carbon sequestration and N output,soil conservation.However,there were significant synergistic effects between water yield and soil conservation,N output,P output and carbon sequestration.The trade-offs / synergies between other ES are not obvious.(4)There is a significant correlation between urbanization and ES,and the correctionbetween landscape urbanization and ES is the most significant(5)The agglomeration relationship between ES and urbanization in urban core area and the ecological conservation area is significantly different,but the relationship in rural areas is not significant.This has a lot to do with the difference of natural conditions and social economic level in Xi'an.