| The Shanghai Green Belt selected as an object in this study, an investigation of artificial vegetation community was carried out using the method of French-Swiss schools and British-American schools.226 seed plant species which belong to 184 genera and 87 families were detected. The artificial vegetation investigated were classified according to the classification system of "Chinese vegetation":The first level was divided according to the community physiognomy; the second level was divided according to the life form; the third level was divided according constructive species of communities and the life form of different layers; the fourth level was divided according to dominant species of different layers. At the same time, aimed at the different community types, the habitat conditions and growth situation were described in order to work out the natural restoration potentiality of artificial vegetation. The main conclusions were as following:1. Species composition characteristics in the regeneration layer(1) 69 seedlings were detected in the regeneration layer of artificial vegetation in Shanghai Green Belt, only Podocarpus macrophyllus which is evergreen coniferous species, Metasequoia glyptostroboides which is deciduous coniferous species were detected,7 evergreen broad-leaved tree seedlings,37 deciduous broadleaf tree seedlings,16 evergreen broad-leaved shrub seedlings, and 8 deciduous broadleaf shrub seedlings were detected.(2)The main regeneration pattern of seedlings in the regeneration layer was seedling and the main dispersal pattern of seedlings was by birds and wind. The woody species mainly were sun species, but shade-tolerant tree species had higher occurrence.(3) The species were much more abundant than down town and Sheshan mountain area due to an appropriate human disturbance.2. The difference of species composition under different community typeThe woody species was the most in deciduous broad-leaved forest and lowest in clustered bamboo. Ligustrum lucidum, Cinnamomum camphora, Pittosporum tobira which were native evergreen tree species, and Broussonetia papyrifera, Morus alba, Celtis sinensis, Koelruteria paniculata, Ligustrum sinense which were native deciduous tree species were the main woody species which had a high occurrence and seedling quantity. Trachycarpus fortunei had the highest occurrence among cultivation species.3. The limitation factors of restoration of artificial vegetationThrough analyzing species composition and habitat factors in different community type, there were seedlings which could maintain regeneration of artificial vegetation, and the habitat and the seed resources were the key limitation of under story vegetation restoration. Owing to habitat fragmentation, seed resources blocked the seedlings dispersal of the zonal vegetation type in Shanghai. Analyzing the relationship between species distribution and habitat in 13 community types, the results indicated that the light intensity, soil temperature and soil wetness were the key limitation of natural restoration under artificial vegetation.4. The potential of natural restoration of artificial vegetationBased on the studies above, the characteristic of main species of population structure which appeared in regeneration layer were analyzed. The main species were classified according to the function and status during the process of natural restoration: Morus alba and Broussonetia papyrifera were pioneer species, Celtis sinensis and Koelruteria paniculata were seral species, Ligustrum lucidum and Cinnamomum camphor a were accompanying species of community. Ligustrum sinense, Distylium racemosum and Pittosporum tobira were shrub accompanying species. It was concluded that the artificial vegetation in Shanghai Green Belt would recover to evergreen broad-leaved forest with the dominant species of Cinnamomum camphora and Ligustrum lucidum under a low insity of man-made interference. And as a result of the seed resources limitation, the artificial vegetation cannot recover to the zonal vegetation type in Shanghai.
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