Studies On Community Structure And Optimized Tactics Of Urban Forest In Suzhou

In accordance with "Urban suburban rural" gradient sampling method, collecting samples according to the differences of the place and the establishment time of each composing part of the urban forest in Suzhou, the dissertation, written between October, 2005 and May, 2008, has, from the perspective of community science and ecology, investigated and analyzed the community structures and bio-diversity of the four typical secondary forest communities, three plantation communities, fifty communities of five types of scenic forest in major parks of Suzhou, thirty-six typical sampled communities in the eighteen squares, forty in the twenty living areas, 12 in the area of out-city River Net, the species composition of eighty-two street trees and fifteen sampled street trees communities, namely 154 sampled communities, and generalized the flora of urban forest in Suzhou by field investigations, sample collecting, and consulting literature. The specific findings are as follows:1.The urban forest in Suzhou shares 737 species (including subspecies)of vascular plants belonging to 473 genera in 167 families, among which there are 38 species of ferns belonging to 26 genera in 19 families, 23 species of gymnospermae plants belonging to 14 genera in 6 families and 676 species of angiospermae belonging to 433 genera in 142 families. Among angiospermae dicotyledoneae plants have 560 species in 348 genera of 123 families and monocotyledoneae plants cover 116 species in 85 genera of 19 families. Xylophyta plants have 694 species, among which there are 393 species of tree, 235 species of shrub, 63 species of climbing plants .Among 612 species of herb, the rate between the one or two-year-old herbs, perennial herbs and liana is 5/9/1.The tropical distribution type dominates the pteridophyte flora in Suzhou in terms of the genus and family distribution types, which is featured as a rather strong tropical tendency. In terms of species, over a half belong to East-Asia distribution type, which proves the similarities between the pteridophyte flora in Suzhou and that in Japan.Spermatophytes in Suzhou are of rich species, and the geographical elements are somewhat complex. The whole flora belongs to temperate and tropical type, while the former predominates absolutely. The value of R/T proves that the flora in Suzhou is kind of tropical originated, carrying apparent transitional characteristics.2. The sampled secondary forest communities are abundant in species and possess relatively stable community structures, and sound eco-benefit provide the possibility for the progressive succession of community. The average species abundance index S is 43.14, the average comprehensive bio-diversity index K is 1.43, and the average leaf area is 20.65. The discovery of the Castanopsis sclerophylla communities, a secondary forest in Mt. Xiang Forest Park, Suzhou, has proved that evergreen broadleaved forest is one of the regional plants and indicated that Suzhou possesses the appropriate climate such as temperature, moisture for the forming of evergreen broadleaved forest, and in the meanwhile, supplied a sample model for the simulation of northern subtropical evergreen community in the plantation communities in Suzhou.3. The plantation forest communities in Suzhou are rather rich in species. The average species abundance index S is 50.3, the average comprehensive bio-diversity index K is 1.62, and the average leaf area is 5.12. The leaf area index of the coniferous and broadleaved mixture forests is obviously higher than that of coniferous forest and Phyllostachys edulis forest, both of which will succeed into deciduous broadleaved forest in the future.4. The plants in every scenic forest community in the ten major parks are rich in species, among which the vertical-covered types are the richest, the average species abundance index S ranking 31.3, and the open-typed is comparatively simplest, the average species abundance index 14.7. Every type community of scenic forest is distinct with structure level .The evergreen and deciduous plants rate vary from 1:3 to 1:2. Cultivated plants take up at least 60 percent.In each type of samples, the species number of the trees generally varies from 1 to 5. In the samples with the same area, the number of trees reduces with the increase of their average height, diameter of tree trunk and crown. The shrub species range from 16 and 23 mainly,among which Bambusa glaucescens, Euonymus japonicus, Pittosporum tobira, Rhododendron indicum, Loropetalum chinensis var. rubrum, are very ordinary. The species number of the regeneration trees is nine or more. The regional plants such as Pterocarya stenoptera dominates the regeneration trees, while Trachycarpus fortunei takes the lead among garden plants. In herb layer, Zoysia tenuifolia is the most vastly used, most highly covered grass, and Ophiopogon japonicus follows. Some wild plants such as Poa annua, Oxalis corniculata, Duchesnea indica are of comparatively high coverage and frequency.In the bio-diversity indexes of all the sampled communities, the abundance index S is directly relevant to the number of trees, shrubs, herbs, so is the value of comprehensive index of biodiversity.5. The species of sampled community in the squares in Suzhou is comparatively simple, but with a rather clear structure layer. The species of trees in each sampled community vary from 2 to 6, among which Osmanthus fragrans and Cinnamomum camphora share the highest frequency, and no more than 60 percent trees grow healthily and strongly. The dominated species in the shrub are: Loropetalum chinensis var. rubrum, Ligustrum ovalifolium spp. , Rhododendron indicum, Ligustrum quihou, and etc. Festuca arundianacea and Zoysia tenuifolia are frequently used ground-covering herbs. The comprehensive index of biodiversity, leaf area index in every community of the squares are relatively low, ranking 0.59 and 1.48 respectively, so their eco-benefits are relatively low.The number of species has much to do with the construction time of the square and the economic condition of its location. Generally speaking, the earlier a square is built and the less developed region it is located in, the simpler the species are.6. The number of plant species in residential areas is not in positive proportion to the establishment of the living area; therefore, the species in newly-built living area are not always rich. The number of species has something to do with the coverage of the living place and their class .The medium-classed and top-classed living area usually apply some exotic plants. The comprehensive index of biodiversity is, to some extent, associated with the grade of the living area, but not proportional.The plant community structure in each residential place is fairly clear, but liana is less employed. Average value of the crowns of the trees crown in aged living places is much higher than that of those with the same diameter of tree trunk in new residential places, which indicates that severe-cutting and head-cutting is a common phenomenon in new living areas.The trees planted in every residential district are ranked with times regularities. The occurrence rate of such fast-growing trees as Cinnamomum camphora, Broussonetia papyrifera, Platanus acerifolia planted in the living area built in 1980s or even earlier is 100 percent while the color-leaf trees and aspect trees are used widely in the residential regions built after 1998. In addition, the maintenance and management of plants in each residential district vary a great deal.7. The plant species of the Qinhuai River Net in Suzhou is relatively simple. The main tree species are Salix babylonica, Metasequoia glyptostroboid.es, Pterocarya stenoptera, Cinnamomum camphora, the shrub species are Viburnum awabuki, Ligustrum ovalifolium 'Aureum', Rhododendron indicum, Nerium indicum, Jasminum nudiflorum, and Zoysia tenuifolia dominate herb species, and hydrophytes and wetland plants are less used. Generally, the community structure of the river net is rather complex, but simpler in the remote places where its landscape effect and eco-benefit are comparatively inferior. The maintenance and management are relatively inferior, so the plants there grow slowly and weakly.8. The species of street trees in Suzhou is not abundant, but most of them are cultivated trees whereas regional trees are rarely planted, thus making them lack regional characteristics. The street trees are generally healthy. Over half of the street trees in the collected data are less than 20cm in diameter, less than 4m in crown and range from 3 to 8m in height. The crowns of quite a few senior trees are heavily cut. Nearly 35 percent street trees' structure is relatively single. The distribution of fast-growing plants and slow-growing plants is not reasonably proportional.Based on the analyzing large amount of collected field-investigation data, by referring to literature and consulting experts, according to Analytical Hierarchy Process, the factors and positions of the comprehensive evaluation index of the urban forest in Suzhou are established; In the system of integrated evaluation index scores are given according to the 18 different factors. In conformity with system, score the 154 sampled communities of the urban forest in Suzhou. As experts see it, the score higher than 70 of a community can be regarded as an optimized model. Furthermore, the dissertation extends and supplements the optimized models as well as the plant distribution.9. There were 77 species belonged to 39 families in this investigated, which separately accounted 23.6% and 10% for the amount of families and species of the Floristic composition in Selected quarries. Among them, arbor accounted for 13 families and 19 species, frutex for 19 families and 22 species, herbage for 21 families and 28 species, and lianas for 7 families and 13 species. Second: there were only Compositae possessed 7 specieses which exceeded 5 specieses, and 11 families possessed between 2-4 specieses, they were Papilionaceae(4 specieses),Rosaceae (3 specieses) ,Euphorbiaceae (3 specieses) ,Ranunculaceae (3 specieses) ,Rubiaceae (3 specieses) ; Gramineae ( 2 specieses)Ulmaceae (2 specieses),Moraceae (2 specieses),Anacardiaceae (2 specieses),polygonaceae (2 specieses), Liliaceae (2 specieses) ;whereas 14 families possesses only 1 specieses. Third: From the point of species' Frequency, the famlily which contain the most is Compositae, whereas the families that held ralatively fewer ones accounted for large porpotion, the families only possessed 1 specieses accounted for 53.8% of the total amount of families.