| Plant community forms basic unit of urban green space, and provides the foundation of ecological function of Urban Green Space System. It also provides the premise of enhancing the richment degree of landscape, and symbolizes the level of city greening effectively. It is absolutely necessarily to design scientific and rational plant community structure for the steady effective and healthy development of green space, therefore , it is significant to study plant community of urban green space for the city's sustainable development and the construction of ecological city. Nanjing and Hangzhou which are known as first landscape citis were studied in this paper, and 102 typical plant communitis that are relative steady were choosed among the primary parks in the cities. The floristic composition of community and the type of community were studied firstly, and so did the ecological structure and the species diversity, and the characteristic of community of urban green space was summed up. Based on the thorough investigation and analysis , 20 typical plant communities were appraisaled on vision and ecological benefit in two cities'park. Secondly, 12 typical plant communities were choosed from the park's plant communities and the ichnography of plant communities'disposal was made, and the rationality of disposal and application of plant communities were further discussed from plant communities'structure and sight effect. In the end, based on the investigation and the result of multifactorial appraisal system, some measures were put forward to existing park's plant communities, and the ways and means of ecological design were further discussed to build plant communities with high ecological effect, abundant species diversity and rational structure. The main results are as follows: 1.In two cities, plant species is abundant and zone indigenous plants play significantly, but it is still lower than total indigenous plants in the region. In 50 sample communities in Nanjing, there are 288 vascular plants belonging to 203 genera in 89 families,which occupy 12.26 percent in existing plants in Jiangsu area.There are 208 zone indigenous plants belonging to Jiangsu, which is about 72.2 percent in all species of investigative range. In 52 sample communities in Hangzhou, there are 394 vascular plants belonging to 267 genera in 111 families, which occupy 10.16 percent in existing vascular plants in Zhejiang area. There are 319 zone nature distributing plants belonging to Zhejiang, which is about 81 percent in all species of investigative sample. The species is more abundant in Hangzhou's park, especially in bush and lawn plants, and zone species is used richly. The cultivated species is planted largely, especially evengreen species. 2. The type of plant communities is various in park of Nanjing and Hangzhou, and the zone of vegetation types is distinct. There are 7 community types in sample communities of Nanjing's park, and defoliation-broadleaf forest which appears regularly in all sample takes 48 percent in all types. There are 6 community types in sample communities of Hangzhou's park, and evengreen –defoliation broadleaf forest which appears regularly in all sample takes 35 percent in all types. The distributing of sample numble of community types is different in Nanjing and Hangzhou's park, and the diversity is notable. 3.In the park of Nanjing and Hangzhou ,the structure of plant communities is multiple structure combined with arbor ,bush and grass on the whole. The species density of bush is denser than the arbor, the ratio of importance value between evengreen and defoliation species distributes among third and three. The diversity of species density of bush is notable between two cities'park, and Hangzhou takes higher than Nanjing on bush, but it is different on arbor. 4. The species of primary and preponderant is rather abundant in plant community of Nanjing and Hangzhou's park, but the frequency of emergence is obviously low. The diversity of composition of primary and preponderant species is notable in two cities'communities. The shrub species is abundant under the communities, but the application in garden is still seldom, only several species is used frequently. 5. Based on relativity analysis and principal components analysis of park's plant communities, there is much more notable correlative between structure factors, and main characters of communities focus on few structure factors of communities. The diversity of main factors which describe park's sample communities in two cities is notable, the arbor's characters occupy main position in Nanjing, and so do the biodiversity factors and characters of shrub in Hangzhou, which showed park's communities have their own feature in two cities. At the same time, the position of more notable relativity which exists in structure factors in sample communities is same, which shows there is orderly relation among structure factors of communities. Furthermore, the main factors which reflect the community's feature in two cities'park involve species diversity factor, overlay's factor between arbor and shrub and community area. The result showed structure factors of these communities acted important rule on communities.6. The species abundance degree and diversity index of communities are very high in two cities'park. In Nanjing's park, the average of species abundance degree in sample communities is 6.8, the average of Margalef index is 1.4324, the average of Simpson index is 0.6304, the average of Shannon-Wienner index is 1.3663, the average of Pielou index is 0.7496, and the average of Berger-Parker index which reflect ecological predominance degree of preponderant species is 0.5020. In Hangzhou's park, the average of species abundance degree in sample communities is 8.4675, the average of Margalef index is 1.8434, the average of Simpson index is 0.7110, the average of Shannon-Wienner index is 1.6149, the average of Pielou index is 0.8138, and the average of Berger-Parker index is 0.4228. The diversity of diversity index is notable in sample communities for the difference of area ,function and the construction time in park's plant communities. 7.The result of multifactorial appraisal showed the sight quality of plant communities was better in Hangzhou's park than Nanjing's park. The average value of multifactorial appraisal on 10 communities is 10.510 in Nanjing, while the value is 11.024 in Hangzhou city. In the end, some advices were brought forward to change afterwards administer and terminal administer as headwaters administer, and to optimize the structure of urban green land communities starting with improving community design and planting structure. The proposition also refer to emphasize science civilization spirit of urban afforestation, and to build healthy, nature and comfortable green space based on the climate of city, soil and underlying vegetation character, construction status of city, the fo undation of economy and culture inside information, so as to play nature control mechanism of communities fully, and it is important to form green land communities with stabilization , efficiency, persistence and economy by means of adopting ecological conservation ways. In addition, the ways of communities'ecological design about "almost nature forest"was put forward from simulation zone vegetation's type, and it is significant to construct high quality plant communities so as to bring nature forest to the city.
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