Landscape Pattern Evolution’s Typical Ecological Effects In A Rapidly Urbanized City

Urbanization is the inevitable trend of global social and economic development,and the future of cities is the future of human beings.To explore the evolution of landscape pattern and typical ecological effect will help to reveal the mechanism of urban spatial expansion,promote the scientific regulation of urban land use,so as to give full play to the function of urban ecosystem,promote the construction of urban human settlements,and ultimately achieve sustainable development.So this paper takes Yangzhou,a fast developing medium-sized city,as an example,based on multi-stage(1995,2000,2005,2010 and 2015)Landsat satellite images and socio-economic data,using landscape pattern analysis,Boosted regression trees and other methods to explore the evolution of landscape pattern and its typical ecological effects in the process of urban development.(1)From 1995 to 2015,cultivated land decreased,woodland,green land and water body changed little,and built-up land area continued to increase.The degree of landscape fragmentation and landscape diversity gradually increase in the process of urban expansion.The form of built-up land undergoes the alternation of "agglomeration" and "diffusion",while the landscape pattern tends to be homogeneous.In terms of landscape pattern,the increase of altitude and population density will promote landscape fragmentation and inhibit landscape agglomeration;the increase of population will promote landscape agglomeration and reduce landscape fragmentation;the role of other factors(distance from the center of a country,per capita GDP and the proportion of secondary industry)will change with the development of the city,such as per capita GDP on landscape fragmentation for the transformation of"promotion→inhibition",the second industry is "inhibition→promotion".In terms of the expansion of built-up land,the geographic spatial factors(such as altitude,distance from the center of a country and built-up areas)have the greatest impact on the expansion of built-up land and the evolution of landscape pattern,but its influence has declined with the development of cities,and the role of social economy has gradually increased.The main effect of geospatial factors on the expansion of built-up land is inhibition,but the effects of different social and economic factors are quite different.(2)From 1995 to 2015,Yangzhou became warmer as a whole,especially in the central and southwest areas,while in the north there was a certain trend of cooling,and the thermodynamic center gradually moved to the southeast.With the development of the city,the relative impact of landscape composition on the thermal environment shows a trend of decreasing first and then increasing,and is always higher than the impact of landscape configuration.In the aspect of landscape composition,the increase of the proportion of built-up land area promotes the temperature rise of the earth’s surface,the increase of the proportion of cultivated land area promotes and then suppresses the thermal environment,and the water body is the obvious cold source;in the aspect of landscape configuration,the increase of patch density promotes the temperature rise of the earth’s surface,the polymerization degree promotes and then suppresses,and the influence of edge density and Shannon diversity index follows the city Urban development changes,such as edge density on both the promotion of thermal environment(2000)and inhibition(2015).(3)From 1995 to 2015,Yangzhou’s low-carbon reserves increased,high-carbon reserves decreased,and the carbon sequestration capacity of the whole region’s ecosystem weakened.Most of the high-carbon reserves areas were concentrated in the southwest and north of Yangzhou City,from the center of Yangzhou to the outside,and the carbon reserves increased.The impact of landscape composition on carbon storage is greater than landscape allocation,and the proportion of cultivated land area has always been the biggest factor affecting carbon storage,which is positively related to carbon storage,while water and built-up land are negatively related.In the aspect of landscape allocation,patch density,edge density and flavor diversity index showed positive effects on carbon storage,while the effect of polymerization degree on carbon storage was first inhibited and then promoted.(4)With the development of the city,the water conservation amount of Yangzhou city gradually decreases,with the biggest decrease period from 2005 to 2010.In 2015,the decrease trend of water conservation amount has been alleviated to some extent,a large number of low water conservation patches disappear in Gaoyou Lake area,and the high water conservation patches reappear.In terms of the effect on water conservation,the water body shows the promotion,the cultivated land shows the inhibition first and then the promotion,and the built-up land shows the inhibition.In the aspect of landscape allocation,the effect of patch density is first restrained and then promoted,and the edge density is negative to water conservation.Finally,the aggregation degree and landscape diversity index are positive to water conservation.(5)Landscape configuration has a significant impact on ecological effect.The degree of landscape fragmentation has a restraining effect on ecological function,and the improvement of landscape diversity is conducive to the function of ecosystem.Therefore,in the process of urban development,we should pay attention to the protection of landscape diversity,curb the fragmentation of landscape,improve the service function of the whole ecosystem,and realize the sustainable development of the city.In this paper,the spatial-temporal characteristics and driving mechanism of Yangzhou landscape pattern evolution and its typical ecological effects are discussed by using the Boosted regression trees method of machine learning.The results show that the enhanced regression tree method can overcome the shortcomings of many traditional statistical methods,quantify the role and relative influence of multiple factors,and has great application prospects in the field of urban development research.