Study On The Near-natural Configuration Models Of Plant Community In Chengdu City

Since entering the 21st century, China's urban development and urbanization process have been accelerating, which obviously has increased the contradiction with urban ecology and environment at the same time. During urban development, how to lay stress on ecological safety, to emphasize ecological civilization, to do well in ecological construction, to thoroughly implement the scientific concept of development, to construct ecological civilization and to build a harmonious society, which have became the major issues of growing concern by the whole society. People urgently need to find a scientific, reasonable and correct way to address these issues and methods. In this context, study on the building ways and means of urban forest system with rational composition, scientific structure and remarkable function and establishing the near-natural configuration models of plant communities in urban forest have important realistic meanings.The study of the near-natural configuration models of plant community was carried out under the background of the lacking of the systematic application of near-natural theory in the building of the urban forest. In this paper, taking Chengdu city as an example, a study on the near-natural configuration models of plant community in urban forest has been conducted systematically and deeply, based on the application of the principle of the Forestry, Ecology, Landscape Architecture and Aesthetics and the theory of the near-natural forest management and the climax community of Vegetation Succession. The method of clustering analysis, interspecific association analysis and hierarchy analysis were used in this paper. Mean while, the advanced instruments, such as WinScanopy2005a, were used for hemispherical image analysis. As a result, the evolution models of near-natural plant community in urban forest, the basic configuration model, several optimized models and the related building technique for near-natural plant community in Chengdu urban forest were obtained.The logical structure and main contents of this paper were as follows:1. This paper put forward the concept of configuration of near-natural plant communities and the basic theoretical framework for the configuration of near-natural plant communities, which was consisted of the principle of the Forestry, Ecology, Landscape Architecture and Aesthetics and the theory of the near-natural forest management and the climax community of Vegetation Succession.2. A study on the seed selection in the configuration of near-natural plant communities was carried out. The community cluster analysis was conducted based on the species composition investigation on the typical plant communities in Qingcheng Mountain and the existing garden plant communities in Chengdu city. Then the compared study on the characteristics of species composition and species diversity was carried out. The top-level community characteristics were clearies through the analysis of plant flora and community superior stand and dominant species. The plant list of typical community in Qingcheng Mountain and the existing garden plant list in Chengdu city were established. The selectable plant list for the construction of near-closed natural community of urban forest in Chengdu city was concluded and summarized based on the definitude of the selection principle and basis for the configuration of near-natural plant communities in urban forest of Chengdu city, which provided plant materials for the construction of near-natural plant communities in Chengdu city.3. A systematic comparison on plant community structure between Qingcheng Mountain and Chengdu city was made in this paper. Based on the field investigation and laboratory testing analysis, the quantitative study of the biotope, including soil physical and chemical properties and microclimate condition, plant community structural characteristics, including canopy structure, mosaic structure and stratified structure, physiognomy, growth status was made, which established the foundation for the building of evaluation model. According to the analysis of interspecific relationship of Castanopsis fargesii community in Qingcheng Mountain, the positively correlated species couples were det, which proved the scientific basis for the configuration of the near-natural plant community.4. This paper built the evolution models of near-natural plant community in urban forest. Its application in Chengdu urban forest was also studied. The evaluation indexes, i.e. 4 rule layers under target layer, 23 indexes of target layer, 44 basic indexes, such as index of species composition, spatial structure, ecological service function and landscape aesthetics, were determined by using the method of AHP. The species composition indexes included species diversity, the proportion of evergreen species to deciduous species, the proportion of needle species to broad-leaved species; the spatial structure indexes included canopy density, level richness, horizontal mosaic structure, etc; the indexes of ecological service function included carbon fixation and oxygen release, cooling and humidification, water conservation, etc. Landscape aesthetics indexes consist of crown form, stem form, leaf and flower, etc. The evaluation model was constructed based on these indexes and their marking standard and index weight. A quantitative study on the comprehensive evaluation of near-natural plant community was carried out based on the marking standard from the investigation indexes of climax community in evergreen broad-leaved forest of Qingcheng Mountain. The evolution results from the plots of Chengdu city showed that comprehensive score was low, arranged from 1.9224-2.9575. The scoring level was mostly centralized in the grade III. The evolution score and level suggested that it was not high level in the rationality of existing and typical plant communities' structure and their play of ecological service function in Chengdu urban forest. It was necessary and reality for the near-natural reconstruction on the most existing plant communities in Chengdu urban forest. Based on the comparison of the plant community between Qingcheng Mountain and Chengdu city and the establishment and application of evolution models of near-natural plant community, the concept of urban forest was further perfected. The urban forest located in and around human inhabited areas gave priority to tree and had plant community with better stand structure, which could also give full play to ecological service function, improve the urban ecology, beautify urban landscape and provide the better place of leisure and entertainment for people.5. The investigation on establishment technique of the near-natural plant community in urban forest was conducted. The existing problems in the configuration of near-natural plant communities in urban forest were described. The guiding ideology and principle of the configuration of near-natural plant community in urban forest was also clarified. The Castanopsis fargesii community with the evergreen broad-leaved forest of low mountain in Qingcheng Mountain was selected to as a reference system of artificial near-natural plant community to construct the basic model of near-natural plant community and its deductive optimization models, such as park green land, attached green land, protective green block, bamboo forest and coniferous forest in urban forest of Chengdu city. The main technical specification for the establishment of near-natural plant community in urban forest was preliminarily established. The development types of near-natural plant community in urban forest were designed based on the construction and technical specification for the optimized models of near-natural plant community in urban forest. The target and indexes for near-natural modification, including plant community function and type, cite condition, species composition and special structure, were also determined. Taking the existing garden plant community in Chengdu city as an example, the artificial plant community with low evaluation grade was selected to be reconstructed.