Study On Types, Distribution Pattern And Seasonal Change Of Weed Communities In Urban Ecosystem Of Shanghai

The study was carried out in the constructed area of Shanghai in spring and autumn respectively. The vegetation survey was conducted and 107 herbaceous species (which belong to 32 families 89 genera) were detected, in which 62.7 percent are annual species (34species are winter annuals and 31 species are summer annuals) and 37.3 percent are perennial species. 31 species were alien and 76 species were natural in Shanghai and regions around Shanghai. 89 genera belong to 14 areal types and 5 variable types. There are great difference between species of spring and autumn. Dominant species appearing in spring only were almost winter annuals. Dominant species appearing in autumn only were almost summer annuals. Dominant species appearing in two seasons were almost perennials.According to the clustering analysis, 34 dominant types can be classified. 9 type groups can be classified according to classification and ordination. On the diagram of DCA ordination, human disturbance weakened along the axis 1 of DCA from the left to the right. Moisture weakened along the axis 2 of DCA from the lower to the upper.According to the clustering analysis, 34 dominant types can be classified. 16 type groups can be classified according to classification and ordination. On the diagram of DCA ordination, moisture strengthened and light weakened along the axis 1 of DCA from the left to the right, human disturbance enhanced along the axis 2 of DCA from the lower to the upper.Except for the light, moisture and human disturbance, succession was also an effect to the formation and maintenance of weed communities. Communities in habitats with high human disturbance were dominated by annuals and perennials which can endure trampling. Communities in habitats without human disturbance were almost dominated by perennials.5 habitat types were induced on the basis of type groups of spring and autumn. They were edge habitat, abandoned habitat with debris, abandoned habitat with soil, habitat with short-lived annuals and habitat with species which can endure trampling.According to the habitat types, weed species can be induced into 5 species groups. In the edge habitat, species were almost perennials which can endure dankness. In abandoned habitat with debris, species were tall perennials of Compositae. In abandoned habitat with soil, species were almost annuals which can endure leanness. Short-lived species appeared in spring in the habitat with human disturbance taking no care of environment effects. Species which can endure trampling were prostrate perennials.