| The pivotal landscape is a landscape area, which plays an important role in the ecological interaction, ecological value and development strategy. It is an important target to study the structure and function of landscape. The pivotal landscape also plays a direct role in planning the urban, constructing the ecological environment, protecting of biological diversity and designing green space. It has a great diversity of types such as resourceful original bio-region, energy-intersection bio-region, ecological sensitive zone, prominent surface features and landscape nodes. The mountain city has special geography, predominant biological diversity and biological frangibility, which makes its particularity of itself.The research objects in this paper contain. One:large tracts of natural, semi-natural areas:the key areas of the central districts of Chongqing, such as Jinyun Mountain, Zhongliang Mountain, Tongluo Mountain, Mingyue Mountain and the central ridge line of hilly (from Eling Park to Pindingshan Park) as well as semi-natural suburban parks and some key parks; Two:eco-fragile districts:the steep slope areas of Zhongliang Mountain and Tongluo Mountain, the water impoundment areas of the east coast of Jialinjiang River and the big opera of Jiangbei. Three:Simulation analysis:including main urban area of Chongqing and its surrounding area. The north and south is bounded by outer ring of urban Chongqing, and the boundary between its earth and west is Zhongliang Mountain and Tongluo Mountain. By means of site surveys and satellite pictures, the types, the components and the distributions of large natural or semi-natural vegetation section of the main urban area of Chongqing have been analyzed; By simulatively analyzing the spatial distribution and characteristics of ecological fragile area in different conditions and observing the change of connectivity index, the important areas that affect the landscape structure most have been found out, which is very important for maintaining the stability of landscape structure and system planning of the urban green land.The results prove that:(1)The pivotal regions with the distribution of large area of natural and semi-natural vegetation are mainly in mountains and hilly. The natural vegetation is mainly distributed by the four mountains, including Jinyun Mountain, Zhongliang Mountain, Tongluo Mountain and Mingyue Mountain. The central ridge line of hilly has semi-natural vegetation.The four mountains contain natural forest land and possesses abundant natural resources, numerous species and forest types. The Jinyun mountain contains many evergreen broad leaved forest and bamboo forest, while Zhongliang Mountain, Tongluo Mountain and Mingyue Mountain mainly have coniferous forest. Within the field of investigation:the Simpson index of arborous layer and shrub layer in Jinyun Mountain is0.93and0.95, respectively, the Simpson index of arborous layer and shrub layer in Zhongliang Mountain is0.80and0.89, respectively.and in Tongluo Mountain is0.93and0.96, respectively. Semi-natural forest zone of vegetation:due to the various species and forest types in the central ridge line of hilly, mainly composed of broadleaved deciduous forest, the Simpson index is relatively higher, with the value of0.89and0.79.(2)Suburban parks and important parks with semi-natural vegetation:including Geleshan Forest Park, Tieshanping Forest Park and Nanshan Botanic Park, mainly has coniferous forests.The significant parks of Zhaomushan Botanic Garden and Hongenshi Forest Park, the Forest land types of which is mainly broadleaved deciduous forest. The vegetation which belong to semi-natural forest land, are rich of vegetation composition and are various of species and forest types.The Simpson index of arborous layerand shrub layer of Geleshan forest parkis are0.89and0.95, respectively ones of Tieshanping Forest Parks are0.81and0.89, the ones of Nanshanbotanic garden are0.94and0.95. ones of Zhaomushan Botanic Garden are0.88and0.85; ones of Hongenshi Botanic Garden are0.88and0.85, respectively.(3)Ecologically vulnerable steep slope areas are mainly distributed by Zhongliang Mountain, Tongluo Mountain and the central ridge line of hilly, which is easy to soil and water loss. The area of two mountains with the slope of15°is21145.8hm". One with the slope of35°is1983.8hm2.the area with the slope of35°is113hm2.The whole rateof forest land covering is54.3%. the non-forest area:The area of15-25°is greater than that of25-35°, area in25-35°is more than that in passed35°.The slope of the central ridge line of hilly:the area with the slope greater than15°is 21145hm2.the area with the slope greater than25°is68.3hm2.the area with the slope greater than35°is10.9hm2.The whole covering rate of forest land is only39.6%. the non-forest area:that of15-25°(50.9hm2) greater than that of25-35°(34.7hm2) greater than that of35°(6.6hm2)。Due to the impact of its slope, the ecological environment in ridges and hilly is more fragile than plains. The interference from outside, the high ratio of construction land and the reducing forest land covering rate adds to the loss of water and soil, increasing the ecological vulnerability of the ridges and hilly.(4) Fragile ecology of water-level-fluctuating zone in Yangtze River and Jialing River. Though the analysis of the water-level-fluctuating zone, the change of the water level, and the distribution of vegetation and habitat characteristics, the conclusion is drawn, the degree of ecological vulnerability:the area with elevation163-165m greater than that of165-175m greater than that of175-185m greater than that of passed185m. The Water flooded time is2-4months in area with elevation163-165m, which has the the most vulnerable ecotope.(5) With the help of software about Gis and Fragstats, simulation were conducted by increasing or reducing the green patch in main town. The analysis results indicate that, there are11important landscape areas found, dislocated in Yubei District and Northern New District. In the11key areas, the connect index raises from0.1385to0.1892and0.2467, with forest area increasing of100hm2,400hm2. Along with the decreasing of large forest patches, landscape connectivity varies much in seven landscape area, among which, the central ridge line of hilly varies most. It decreases from0.1385to0.1306and is the most pivotal landscape area. |
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