Urban Spatial Expansion And Urban Vegetation Growth Change In China

As a gathering center and space carrier of politics,economy,and culture of the country or region,thechange of the city's ecological environment has always been a common concern of the public and research staff.In particular,with the accelerating process of urbanization in China,the urban population is rapidly expanding,the urban space is constantly expanding,and the growth of vegetation within and around the city has also undergone tremendous changes.The contradiction between the expansion of the city's space and the ecological environment has intensified.The leaf area index(LAI)refers to the total unilateral area of plant leaves on a unit area of land.The LAI can be used to evaluate the vegetation growth status of the city.In the past,the urban spatial expansion study focused on the spatial and temporal characteristics,driving mechanisms,land use changes,and simulation predictions of urban spatial expansion.This study uses all cities in China as research objects and combines LAI with urban spatial expansion to intuitively evaluate urban vegetation growth.The change.This study not only analyzes the changes in land use in all cities in China from 2000 to 2015,but also changes in LAI in the old urban areas,new urban areas,new and old urban areas,and its urban buffer zone,and at the regional level.The analysis of LAI trends in the 32 central provinces and cities in the country,while conducting a comparative study of the changes in vegetation growth from 2000 to 2015 in the overall and regional perspectives,in order to explore its processes,laws and mechanisms.The specific findings are as follows:(1)LAI demonstrated good applicability in the study area.This study used the 2000 LAI data as validation data.In the study area,there were a total of 46 LAI data with a time resolution of 8 days in 2000.This study randomly selected 6 points from 46 superimposed LAI data(points are distributed in Hainan Province,Sichuan Province,Henan Province,Jilin Province,and Xinjiang Province respectively.The Uygur Autonomous Region and the Tibet Autonomous Region will use the annual LAI values of these six sample sites as their time series charts.The analysis shows that the time series diagrams of the selected six sample points all conform to the dynamic changes of seasonal vegetation changes in the spatial pattern of the point where the spatial pattern is located,and the LAI data has good long-term continuity characteristics.(2)In the process of urbanization in China,urban space is expanding rapidly.From 2000 to 2015,the urban land area increased by 19197.0 km~2,with an average annual increase of 1279.8 km~2.In 2000,the urban area accounted for 0.16%of the national land area,and it increased to 0.25%by 2015,an increase of 1.56 times.The highest contribution rate of cultivated land is 71.73%,and the occupied area is 13770.0 km~2,followed by construction land,forest land,grassland,water area and unused land.The rapid development of social economy,the continuous increase of urban population,the construction of infrastructure,and planning and policies have become the main driving forces for the rapid expansion of urban space.(3)The average decline rate of LAI of vegetation in 32 central cities is faster than that in other cities. From 2000 to 2015,the slopes of the LAI means-fitting lines of all cities in the country and the 32 old cities in the old cities were-0.0027 and-0.008,respectively.The LAI of the two cities both declined in the research time series,and 32 centers.The average slope of urban LAI-mean-fitting line is about 2 times that of all cities in the country.Comparative analysis shows that the average LAI of vegetation throughout the old urban areas of the country is in a downward trend,and the rate of decline of the 32 central cities is faster than that of other cities.However,through separate analysis and analysis of 32 central cities,the average LAI values of the old cities in 12 cities including Beijing,Tianjin,and Jinan are on the rise.In short,the average LAI of all vegetation in all cities in China and in32 central cities is in a decreasing trend,but individual cities still have a rising trend.This shows that some cities have affirmed the management and maintenance of vegetation in the old city,but most cities still need to be strengthened.(4)The average LAI decline rate of the vegetation in the 32 central cities and other cities is comparable.From 2000 to 2015,the slopes of the LAI mean line for all cities in the country and 32 new urban centers were-0.021 and-0.019,respectively.The LAI of both cities declined during the study time series,and both declined.The rates are almost identical,indicating that 32 central cities have plans similar to other cities for the new city.Through the separate analysis of 32 central cities,the average LAI of all new urban areas is in a downward trend.Without exception,it shows that in the process of the construction of new urban areas,other types of land with vegetation coverage will be transformed into inevitable construction land.Irreversible damage to the vegetation.(5)The rate of decline of the LAI average of the overall 32 urban centers and other urban areas is almost the same.From 2000 to 2015,the slopes of the LAI mean line of the overall city-wide metropolitan cities and the 32 central cities were-0.0082 and-0.007,respectively.The LAI mean values of the two cities were not significantly different from each other,indicating 32 central cities in the study time series.The average LAI of vegetation with other cities is in a downward trend,and the rate of decline is almost the same.However,the average LAI of the entire new and old urban areas of Beijing and Taiyuan City is on an upward trend,indicating that even if the development of new urban areas cannot avoid the destruction of large areas of vegetation,as long as the management and maintenance of the vegetation in the old urban areas and the development of new urban areas are strengthened.With the protection of medium vegetation,the average LAI of vegetation in the city can still maintain an upward trend.The buffer zone in the urban area is more influenced by the natural environment than the interior of the city.In this study,LAI mean value extraction and analysis of the area of the 10km buffer zone in the urban area show that all of them are in an upward trend,and indirectly also indicate that environmental factors are more and more conducive to the growth of vegetation.In short,this study uses a combination of theories and techniques of ecology,urban science,and geographic information science,and uses LAI data,RS data,GIS data,socioeconomic data,and other multi-source data,from all cities in the country,and 32 provincial and regional centers respectively.The city's old urban areas,expanded new urban areas,urban areas as a whole,city buffers,and other measures have been sequenced from2000 to 2015 for a long period of time to compare and analyze the process,laws,and mechanisms of vegetation growth before and after urban expansion,aiming at urban ecology.Construction and sustainable development provide scientific basis.