| Chongming Island is not only the third-largest island in China but also the world's largest estuary alluvial island. Rich land resources and unique geographical position make it Shanghai's most strategic development space. Since the programme of "making a good preparation for developing Chongming" was proposed in2002, the pace of town construction in Chongming Island has sped up. Great changes took place in land use and human-land conflict became increasingly outstanding. The ecological environment was damaged to various degrees and became more vulnerable and sensitive. The potential threat of ecological environment has become the main obstacle to its economic and social sustainable development. Therefore, with construction of ecological Chongming, doing research on the characteristics of the land use and landscape pattern as well as its dynamic evolution, and making ecological sensitivity analysis and evaluation of Chongming Island is of great theoretical significance and practical value.Supported by ArcGIS and ENVI software, this paper obtained three years'land use type distribution maps through screen digitalization based on Chongming Island high-resolution airborne remote sensing images of the year2005,2008and2012. Using statistical analysis of ArcGIS and mathematical models, we calculated the rate, dynamic degree and the composite index of land use change of different periods. We got characteristics of land use structure and its space-time dynamic evolution of Chongming Island during2005-2011. Through landscape pattern analysis, the characteristics of landscape pattern and its space-time dynamic evolution of Chongming Island were received by calculating various indexes of landscape pattern features. On the basis of above researches, the ecological sensitivity of Chongming Island was analyzed and evaluated using single factor and multi-factor comprehensive method. Then the sensitivity distribution maps of five typical ecological environment problems (including land use, soil erosion, flood, land salinization and habitat conditions) and comprehensive ecological environment of Chongming Island were obtained. This is helpful for Chongming Island's ecological construction.The main results of the paper are as follows:1. In the aspect of land use:Chongming Island's total area increased sustainedly. The total area in2005,2008and2011were respectively1287.451km2,1298.623km2and1299.796km2, with12.345km2increased during the six years at a slower growth rate. The farmland decreased continuously from816.292km2in2005to810.1km2in2011, and the annual average reduction was2.064km2with the proportion reducing from63.404%to62.325%. Agricultural facility land, waters and water conservancy facility land, industrial land, residential land, public management and service land and traffic land increased obviously, the increasing amounts were respectively4.655km2,5.96km2,4.191km2,15.161km2,0.628km2and2.286km2. The area of wetland and forestry grew continuously as well and the increment is separately6.863km2and2.803km2. Various land types in different research period show different change disciplines. The dynamic degree of industrial land and public management and service land in2008-2011was greater than that in2005-2008, while the dynamic degree of other land types in the late research stage was less than that in the early research stage. As for the land mutual transformation, farmland was one of the main sources. Its total outflow was31.564km2, with area of13.135km2transformed to residential land, public management and service land, industrial land, and traffic land in the proportion of41.61%; While area of2.397km2,4.219km2,5.649km2were separately transformed to garden, forestry and agricultural facility land in the proportion of38.86%, and meanwhile area of6.164km2was transformed to other land, waters and water conservancy facility land. The conversion trend between agricultural land (including farmland, forestry, garden and agricultural facility land) was evident. Overall, Chongming Island had a high land use degree. There were significant regional differences between various land use types in different functional district.2. In the aspect of landscape pattern:During the research period, the number of patches reduced1153. The patch's average area increased from27623.07m2in2005to28596.045m2in2011. The increment of average area of wetland was164127.814m2, while the average area of construction land type increased with centralized tendency. The value of landscape diversity index decreased from1.38031to1.34218, showing that Chongming Island's landscape had a tendency to concentrate to a few land use types. The landscape fragmentation showed a slightly increasing trend, indicating that the research area was disturbed by human activities more severely. The fragmentation degree of various land types had different variation disciplines. The fragmentation degree of public management and service land, residential land and agricultural facility land was higher. The largest patch index value of waters and water conservancy facility land, wetland and farmland was much higher than that of the other land types, so they belonged to dominant landscape types. The fractal dimension value of construction land which had regular shapes was close to1, indicating that it was highly influenced by human beings. The shape index of most land types showed a downtrend, indicating that the land use of Chongming Island tended to be compact during the research period.3. In the aspect of ecological sensitivity:After analyzing and evaluating the ecological sensitivity of five typical ecological environment problems, including land use, soil erosion, flood, land salinization and habitat conditions, the comprehensive eco-environment sensitivity was analyzed and evaluated. The results are as follows:(1) There did not exist insensitive region.(2) The extremely sensitive region, whose area was133.788km2in the proportion of10.293%, was proposed to divide into non-development district. Any activities detrimental to the eco-environment should be prohibited so as to strengthen the protection of natural environment.(3) The highly sensitive region, whose area was107.13km2in the proportion of8.242%, was proposed to divide into restricted development district. Some measures like strengthen water infrastructure constructions,afforestation and so on should be adopted so as to achieve positive interaction between ecological protection and economic development.(4) Moderately sensitive region, which covered the widest extent, accounted for73.034%of the total area. It was proposed to divide into moderate development and construction district. The goal of "efficient economy, beautiful environment and harmonious ecology" should be pursued. In order to ensure harmonious development of the environment, society and economy, ecological agriculture and tourism agriculture should be promoted.(5) The area of mild sensitive region, whose area was109.584m2in the proportion of8.431%, was proposed to divide into depth development and construction district. Such types of land like residence, infrastructure and so on could be developed according to the needs of social and economic development, and the principles of combining development and ecological environment protection must be followed. |
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