Study On Land Use And Its Landscape Ecological Change In Lanzhou Main Urban Area During 1961-2015

Lanzhou is one of the major metropolises in western China and an important national petrochemical industry base and integrated transport hub,and even more important,Lanzhou will become an importance economic and trade platform for Chinese with Central Asia and Europe under the development of the Belt and the Road.Since ancient times,Lanzhou always has a special and important strategic position in the military,transportation and geopolitics of China.In the last century of from the end of 50 s to the beginning of 60 s,Lanzhou was rapid development a modern industrial city from a town that relatively backward economy and urban construction.Then under the guidance of the Reform and Opening up and the Great West Development Strategy as well as the Belt and Road policy,the urban construction and urbanization level of Lanzhou city is significantly improved,especially the growth of urban population and the sprawling of urban built-up.Different from the plain city,the built-up area of Lanzhou is located in the valley basin of the Yellow River,so the urban spatial strictly limited by the river valley topography.In recent years,the built-up area of Lanzhou city is filled with the whole river valley basin and sprawled from the valley plain to the mountainous region which restricted construction area.More unfortunately,in the process of urbanization in the past half century,a large number of high quality cultivated,orchard,wetland and ecological land in the the Yellow River valley basin were encroached by the expansion of built-up area,which lead to the deterioration of ecological environment and landscape is facing severe challenges in Lanzhou City.In order to study the urban land use change and its effect on urban ecological landscape in the process of urbanization,this study takes the valley basin of Lanzhou as the study area.Based on the detailed interpretation of various high resolution aerial photographs,remote sensing images,digital topographic maps and Google Earth images with high resolution from 1961 to 2015,the spatial-temporal pattern and the transfer scale as well as landscape ecological health of land use in Lanzhou were analysis by using GIS spatial analysis,landscape ecology and ecological health assessment methods.Through this study,on the one hand,the study results will provide the reference information to the Lanzhou city planning;on the other hand,the study methods will provide valuable experience for ecological health assessment of urban land use change in urbanization process.The main conclusions of this study as follows:(1)From 1961 to 2015 year,the mainly characterized of land use change in Lanzhou valley basin was the growth of urban built-up area,rural settlement land,forest and urban green and the declining of cultivated land,grassland,water area and wetland,especially the expansion of urban built-up area and the reduction of arable land is the most significant.During past 54 years,the urban built-up area increased from 51.26 km2 to 130.22 km2,expanded by 2.54 times,and the proportion of the study area increased from 21% to 53%.At the same time,the area of arable land decreased from 74.20 km2 to 3.84 km2,decreased by 19.32 times,and the proportion of the area decreased from 30.43% to 1.56%.The structure of ecological land use,forest and urban green land increased,but grassland,water area and wetland decreased.The area of forest increased from 21.78 km2 to 35.36 km2,and the proportion increased from 8.93% to 14.50% in the study area.The area of urban green space increased from 1.71 km2 to 12.10 km2,expanded 7.07 times,though the scale was the smallest,the growth of area was the largest in all types of land,the proportion increased from 0.70% to 4.96% in the study area;grassland area decreased from 60.32 km2 to 39.17 km2,the proportion also decreased from 24.74% to 16.07% in the study area.The proportion of water area and wetland in the study area decreased from 12.78% in 1961 to 5.69% in 2015;the area of rural residential area increased from 3.34 km2 to 9.26 km2,and the area proportion increased from 1% to 4%.(2)From 1961 to 2015,the most significant land use conversion is the cultivated land,grassland and woodland into the urban built-up area.The extended area of urban built-up area converted by farmland was 41.48 km2,grassland was 19.50 km2,forest land was 9.61 km2,water area was 7.45 km2 and wetland was 4.79 km2,accounting for 50%,23% and 11% of the net built-up area respectively.And the wetland area and water area accounted for about 15%.(3)Around 1998,the watershed of the urban built-up area of Lanzhou City changed from stable growth to rapid expansion.In the four districts of the study area,Chengguan had the largest proportion of urban built-up areas and was relatively stable,accounting for 39% in different periods.The area of Anning was the smallest but the fastest growing area which grew from 6% in 1961 to 17.29% in 2015.The proportion of Xigu and Qilihe was relatively stable.In the specific direction of spatial expansion of urban built-up areas,eastward expansion was the most significant,followed by the extension of northwest.It means the main areas of urban built-up area expansion occurred in Chengguan and Anning district.That was the main area of urban built-up area expansion occurred in the Chengguan and Anning.After a comprehensive analysis of urban planning and extension of urban built-up area and population,economy and historical edition of Lanzhou in the past more than half a century,this study considers that the urban spatial expansion of Lanzhou City is mainly carried out in the approach of Industrial Parks,Development Zone and New City under the guidance of the government.The government policy dominated the direction and the way of Lanzhou's urban space.The population had a direct effect on the urban built-up area expansion.The driving effect of the economic development on the spatial expansion of urban built-up area was weakening.(4)From 1961 to 2015,the ecological quality of urban landscape in Lanzhou is in a deteriorating trend.The average area and the largest area of all kinds of land patches were significantly enlarged,and there was a obviously trend that the area of patches are polarization and equalization.The landscape fragmentation of the main ecological land was increased,the index of the biodiversity and the physical connectivity between the ecological land were decreased.From 1961 to 2015,although the total area of forest land was increased,the growth of the forest land was mainly from the conversion of grassland,and with the extension of urban built-up area,the forest land was divided and separated frequently,it increased obviously in the landscape fragmentation;Other types of urban land were not only decreased in scale,but also reduced in the physical connectivity of the ecosystem such as grassland,water area and wetland,especially in the range of 2 km.From the view of landscape index,although the landscape ecological function of urban green land tends to be healthy,but it is difficult to play the same ecological function of forest land and grassland because of the smaller scale and patch area.(5)From 1961 to 2015,the urban landscape ecological health index(UEH)showed a U-shaped change.The change of UEH was affected by the urban land ecosystem vitality(V),organization(O),resilience(R)and land ecosystem service value(ESV).These four aspects together affect the health trend of the urban landscape ecological.Although landscape ecological health has a good trend in recent years,landscape ecological health of Lanzhou has been declining in the first 31 years of 54 years and fluctuating in 1992-2015,The main reason for this rise is the development of urban economy,the increase of the urban green space and the improvement of ecosystem services index,urban landscape ecology has not been improved in essence.From the landscape ecological health evolution of the four districts in Lanzhou City,the landscape health from good to poor in the order was Anning,Chengguan,Xigu and Qilihe district.In the end of this study,it is suggested to improve the coverage of urban greenbelt in Lanzhou urban area,and to enhance the landscape connectivity of urban greenbelt and surrounding woodland,grassland and water and wetland,which is an important measure to improve the function of urban ecosystem in the urbanization background.