The Study Of Structure Characteristics And Species Diversity Of Urban Forest In Baoding Urban Area

Urban forest structure (species composition, tree size and health, number and location of trees, etc.) is the three-dimensional spatial arrangement of vegetation in urban areas, which it provides the basis information to comprehend integratively the urban forest ecological functions and to be utilized for city ecological layout. Tree species diversity of urban forest(tree species richness, diversity, evenness and dominance, etc.), on the other hand, is the important index for reflecting the stability and health condition of urban forest community in terms of complexity and organization of urban forest community structure and function. In order to provide basis information to instruct urban forest construction, the structure characteristics and species diversity of urban forest in urban area were investigated by sampling plots in 106kim~2 of the Baoding urban area. There are some important indices about different forest that, including urban forest area, species composition, DBH classes, health condition and LAI of the tree community were analyzed as well as it were conducted by diversity comparison. The main results are showed as follows:1 The gross of urban forest in Baoding urban area is at a low-level stage, although it can provide basically ecological benefit. Furthermore, there is obvious difference between urban forest types. For example, the protective forest surrounding of city zone provided the most of ecological benefits whereas the residential area forest almost has not benefits because of it low density.2 There are 98 tree species that they were detected, which are respectively belonging to 65 categories of 35 families. Among them, there are 13 species (belonging to 3 families) of Gymnosperms and 85 species (belonging to 32 families) of Angiosperms. Among them, only several species mount took dominant station, which led to the plant monotone and the ecological unsteadiness of urban forest.3 The constitutes of urban forest in Baoding were those of young stand, of which those BHD less than 10cm take up 71.5%. Less-managed forest lands (e.g., residential area forest land, public forest land) had the highest proportion of small trees, whereas intensive-managed lands(e. g., street trees, institutional/enterprise forest land), particularly those managed for a relatively long period, tend to have a higher proportion of large trees.4 The total health of urban forest investigated in Baoding was classified as being in medium condition. The sequence of health condition from higher to lower in different urban forest types is institutional/enterprise forest＞protective forest＞residential area forest＞street trees＞scenic forest＞public forest. The factors related to health of forest, besides protection, are thesis of surroundings stresses (e. g., salt, soil compaction, vandalism, injury), plant competition (related to tree density) and natural aging processes (tree size).5 The leaf area index(LAI) between different urban forest types was significantly difference, and the sequence is that protective forest is of 6.37, street tree of 5.5, institutional/enterprise forest of 3.39, scenic forest of 3.16, public forest of 2.03 and residential area forest of 1.2. The five greatest average leaf-surface area on a per tree basis occurs on Populus tomentosa, Sophra japonica, Platanus acerifolia, Cedrus deodara , Ailathus altissima. These five species most likely have the greatest impact on the surrounding environment.6 Among six urban forest types in Baoding urban area, from the amount of tree species, the number of residential area forest take place the biggest one whereas the number of protective forest is the least. The tree species diversity index is similar in different urban forest types. The evenness index, on the other hand, there is also a few different among them but highest in institutional/enterprise forest and lowest in street trees.7 There is a tendency in diversity index among different layers of urban forest community, in which the complicated composition community has a higher trees amount in different stand layers in compare with the simple one. Among the different layers of urban forest community, the indices in tree layer are higher than in shrub layer. The indices in tree layer are similar in communities, but it is significantly difference between shrub layer and communities.8 Based on both information of urban forest structure and tree species diversity, an assessment was proposed reasonably. And finally, some suggestions about urban forest of Baoding, for example different forest type distribution and arrangement, the selection of trees, public participation and et al, were put forward.