Studies On The Ecological Effects And Optimization Of Unban Forest Communities In Shanghai City

Based on the theory and practice of urban forest construction home and abroad, this paper undertaked an analysis and an assessment of Shanghai's environmental factors such as its ecological environment, integrative natural conditions, land use types, industrial outlay, air pollution, water pollution, soil pollution, with typical urban forest as its research objective. Urban forest design and arrangement and urban forest structure layout were carried out with a combination of qualitative and quantitative analysis methods. At the same time, this paper also undertaked research on the ecological functions of urban forest and the choice of virescence plant species. Some measurements for improving the qulity of Shanghai's urban forest construction were put forward. The suggestions could provide a theoretical foundation for driving the tenor of Shanghai's urban forest construction, and for improving the layout and the ecological functions of its urban forest. The main conclusions were described as follows:(1) The values of urban forest structure index, urban forest function index, urban forest coordination index and urban forest comprehensive index in Shanghai was 0.48, 0.46, 0.60 and 0.48, respectively. The coordination capacity of shanghai's urban forest was relatively good, but its integrative indexes was a little lower, far below the ideal functioning of a forest's ecosystem service functions. The forest coverage rate, air environment quality, water and soil conservation, environmental capacity of landscape, water and forest networks, the compatibility of landscape required to be improved.(2) Among the city parks investigated in Shanghai, the thermal effects of 80% of the parks were above that permitted. More than 80% of the parks had a higher cleanness than cleanness grade permitted. Most parks had a bryophytes BI grade level above grade D. All other parks had an integrative natural ecological function above grade D except Jing'an Park and Huaihai Park.(3) Presently in Shanghai urban forest total volume of alive standing trees was 2.752×106m3,with a yearly growth rate of 3.01×105m3 and an average CO2 absorbing ability of 5.036×106t, resulting in an economic effect of 27.55 million yuan. Annual O2 release by forest was 4.88×105t, covering 10.9% of its breathing consumption, producing an economic effect of 342 million yuan. The 8.92×104 hm2 forest land in Shanghai can store 880 million tons of water peryear, with an economic effect of 792 million yuan. The total amount of soil conservation in Shanghai came to 2.178×107 m3 peryear, with its economic effect coming to 650 million yuan.(4) The most common tree in greenland communities was Cinnamomum camphora, with its emergence frequency of 0.27, higher than that of other trees by far. Populus canadensis cv. also showed a relatively high emergence frequency of 0.13, but the densities of many Populus canadensis cv. forest were too high, with a simple community structureand poor stability. So it is need to transformate the species composition and forest form in the near future. The other trees with relatively high emergence frequency were Ligustrum lucidum, Cedrus deodara, Metasequoia glyptostr-oboides, Magnolia grandiflora, Platatnus orientalis L., Elaeocarpus glabripetalus, etc. Some trees with low emergence frequencies were used in the past such as Robinia pseudoacacia, Bischofia polycarpa, Gleditsia sinensis, Ulmus parvifolia Jacq., Pterocarya stenoptera DC. are becoming less applied.(5) According to structure and function relationship priciples, and main functions of urban forest, four models of urban forest structure were proposed: ornamental forest community model, environmental protection model, production forest community model, and leisure and culture model.(6) Only 3 types of trees had an emergency frequency higher than 30%, including Cinnamomum camphora, Magnolia grandiflora and Buxus sinica (Rehd. et Wils.) Cheng ex M. Cheng. With frequencies ranging from 1% to 20%, appeared a relatively larger number of tree types, 57 types altogether. With frequencies ranging from 1% to 5%, appeared the largest number of tree types, 24 types altogether. in our investigation, only a small number of types of trees such as Sapindus mukorossi Gzertn., Aesculus chinensis and Myrica rubra (Lour.) Sieb. et Zucc. appeared with a emergency frequency lower than 1%, while 24 types of trees appeared with a emergency frequency higher than 10%, covering about one third of regularly used tree types.(7) In towns of Shanghai city, especially in the area connecting the town with its suburb, the garden plant community had a relatively high diversity. Suburban virescence had not attracted enough attention. In some remnant land around villages natural plant communities remain, with rare types of home trees and some economical fruit trees composing some simple communities, such as Melia azedarach, Ulmus pumila, Broussonetia papyrifera, Metasequoia glyptostro boides, Salix babylonica, Phyllostachys praecox C.D.Chu et C.S.Chao, Eriobotrya japonica, Ficus carica L., Citrus microcarpa, Prunus persica, etc.(8) A classification investigation of the present trees was carried out according to the growth adaption indices and conditions of urban forest site. The result showed that such trees as Platatnus orientalis L., Viburnum awabuki, Aucuba japonica Var. iegata, Distylium racemosum, Acer palmatum Thunb., Metasequoia glyptostr-oboides, Cinnamomum camphora, Pittosporum tobira, Pterocarya stenoptera DC., Albizia julibrissin Durazz, Sophora japonica L., Ilex chinensis Sims., Liquidambar formosana, Ligustrum quihoui, Jasiminum nudiflorum, Myrica rubra (Lour.) Sieb. et Zucc. grew well. The trees that were used with a relatively low frequency were Quercus aliena Blume, Pistacia chinensis Bunge, Sapindus mukorossi Gzertn., Sapium sebiferum, Zelkova schneideriana, Toona sinensis, Schima superba Gardn et Champ, Cryptomeria japonica, Torreya grandis, etc. In the selection and plan of existing tree species in Shanghai, the effect of soil moisture property and soil pH on the trees species growth could be considered as key factors.