Studies On Community Structure And Optimized Models Of Urban Forest In Nanjing

Studies on Community Structure and Optimized Models of Urban Forest in NanjingIn 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 Nanjing, the dissertation, written between September, 2004 and April, 2007, 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 ten major parks of Nanjng, thirty-six typical sampled communities in the eighteen squares, forty in the twenty residential areas, eleven in the area of Qinhuai River Net, the species composition of eighty-four street trees and fifteen sampled street trees communities, namely 159 sampled communities, and generalized the flora of urban forest in Nanjing by field investigations, sample collecting, and consulting literature. The specific findings are as follows:1.The urban forest in Nanjing shares 1500 species (including subspecies)of vascular plants belonging to 572 genera in 172 families, among which there are 63 species of ferns belonging to 36 genera in 25 families, 54 species of gymnospermae plants belonging to 23 genera in 8 families and 1383 species of angiospermae belonging to 513 genera in 139 families. Among angiospermae dicotyledoneae plants have 1156 species in 395 genera of 114 families and monocotyledoneae plants cover 227 species in 118 genera of 25 families. Xylophyta plants have 694 species, among which there are 393 species of tree, 235 species of shrub, 66 species of climbing plants. Among 806 species of herb, the rate between the one or two-year-old herbs, perennial herbs and liana is 4∶9∶1.The tropical distribution type dominates the pteridophyte flora in Nanjing 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 Nanjing and that in Japan.Spermatophytes in Nanjing 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 Nanjing 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 44.75, the average comprehensive bio-diversity index K is 1.49, and the average leaf area is 20.53. The discovery of the Castanopsis sclerophylla communities, a secondary forest in Mt. Niushou Forest Park, Nanjing, has proved that evergreen broadleaved forest is one of the regional plants and indicated that Nanjng 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 Nanjing.3. The plantation forest communities in Nanjing are rather rich in species. The average species abundance index S is 35, the average comprehensive bio-diversity index K is 1.27, and the average leaf area is 4.97. 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 27.7, and the open-typed is comparatively simplest, the average species abundance index 16.8. Every type community of scenic forest is distinct with structure level. The evergreen and deciduous plants rate vary from 1∶2 to 1∶3. Cultivated plants take up at least 60 percent.In each type of samples, the species number of the trees generally varies from 1 to 6. 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 19 and 25 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 ten or more. The regional plants such as Pterocarya stenoptera dominates the regeneration trees, while Trachycarpusfortunei 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 Nanjing is comparatively simple, but with a rather clear structure layer. The species of trees in each sampled community vary from 3 to 6, among which Osmanthus fragrans and Cinnamomum camphora share the highest frequency, and no more than 70 percent trees grow healthily and strongly. The dominated species in the shrub are Buxus sinica, Loropetalum chinensis var. rubrum, Ligustrum ovalifolium 'Aureum', 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 as well as the plant distribution.