The Comparatively Study On Woods Composition And Structure Characteristics Of Woody Plant Communities In Central Districts Of Chongqing

The woody plant communities of city, as one type of communities that are closely connected with the city environment, are the production of modem forestry and modern gardens, and are the important part of city greenbelt. This article bases on different human-caused disturbance to classify the city woody plant communities into three types, Namely the natural type, the half-natural type and the artificial type. The natural type chooses the evergreen broad-leaved forest community of Castanopsis carlesii and Machilus nanmu in Jinyun Mountain nature reserves, the half-natural type chooses the plant community of Cunninghamia lanceolate and Symplocos setchuanensis, the artificial type chooses the woodlands in Flower garden and Dadukou park. Compared the characteristics and differences of the three types woody plant community in the species composition, size structure, diameter of bosom height(DBH), and distribution pattern etc. Contrasted with natural and half-natural type, And analyzed the characteristics and possible problem of artificial woody plant community in the central district, providing the phytocoenology basis for the scientific constructing of artificial woody plant community in central district of Chongqing.The primary conclusions are as follows:1) The species composition of the varied woody plant communities:①The ranking of the dominance and the species richness of the three type is the natural type＞the half-natural type>the artificial type, but the dominance species quantity is other vise .②The species diversity index and the evennes index of the four plots in three type are all relatively big, but the diversity of the artificial type is least and the evennes of the nature type is small.2) The structure of the woody plant communities:①Compared with the natural type of woody plant community, the evergreen arbor and shrub's species and quantity of artificial type are relatively small, for more attention is paid to the varied layer species and ignores the quantity.②from the distribution of the varied height classes of trees. Compared with the natural type, most of the artificial type plants are small arbors. No arbors higher than 15m exist, the height is from 1m to 2m.③the DBH distribution of tree is similar to that of height, the natural type is progressive, the nature type is stable, and the artificial type is declining . Compared with the natural type, the portion of big tree (DBH>20cm) is small in the artificial woody plant community. The tree quantity in the artificial plots drops rapidly with the growth of the DBH. When DBH>30cm, the portion is less than 5%. 3) the plot difference analysis: the analysis of the seven index's variation coefficient (species of arbor and shrub, diversity of plants, cover of plant and the overall woody plant species ) in four plots shows that, the natural type the wildwoods> the artificial woods. The DBH area of the four sample plots are all bigger than 5.5m~2/hm~2, reaching the standard of 5.5m~2/hm~2, but from the differences between the nature type(21.25m~2/hm~2), the half-natural type(30.13m~2/hm~2), and the artificial type(the flower gardenl2.21 m~2/hm~2, Dadukou park 6.87m~2/hm~2), even though the artificial type already has some characteristics of the "forest", but under some conditions, we can improve the biomass and the DBH area of artificial type through human-caused simulation of the natural typ(?) species constitution and the space structure, and then improve its ecological benefit at last.