Study On The Natural Restoration Potentiality Of Artificial Vegetation In Central Shanghai

The dynamics of species composition and diversity,population structure and height growth rate of understory vegetation in the Metasequoia glyptostrobodies plantations abandoned for 5,8 and 12 years in the campus of East China Normal University has been studied in this paper.The results indicated that 1) the species diversity decreased after abandoned,2) understory vegetation mainly distributed on the layer of 0-1.5m and 1.5-3.0,in which the main species is Trachycarpus fortunei due to rich seeds sources,3) the population structure pattern shifted from sporadic type to unimodal type,and its restoration has been changing into deflected succession, and 4) Trachycarpus fortunei and Ligustrum quihoui with the character of shade-tolerant have fast height-growth rate.It was suggested that the habitat,the seed resources and the seed dispersal pattern were the key limitation of understory vegetation restoration.In order to validate the key limitation of understory vegetation restoration are the habitat,the seed resources and the seed dispersal pattern,and infer the natural restoration potentiality of artificial vegetation,an investigation and analysis on artificial vegetation of different vertical structures in central Shanghai was done on the basis of above studies,and 277 seed plant species which belong to 203 genera and 97 families were detected.The artificial vegetation we investigated were classified according to the classification system of "Chinese vegetation":The first level was divided according to the community physiognomy;the second level was divided according to the life form;the third level was divided according constructive species of communities;the fourth level was divided according to dominant species of different layers.Using PC-ORD software,herb communities investigated in spring and autumn have been grouped into 24 and 28 types with the method of cluster analysis.Based on the above classification,the artificial vegetation was divided into tree-shrub-herb,tree-herb,shrub-herb,and herb community according to the vertical structure.At the same time,aimed at the different community types,the habitat conditions and growth situation were described in order to work out the natural restoration potentiality of artificial vegetation.Analysis the biodiversity,species composition of seedlings,the seed dispersal pattern,and the relationship between the seedlings and the habitats in regeneration layer of different structures of plant communities.The results indicated that:1) The Shannon-wiener index(H) of different structures of plant communities from high to low were tree-herb,tree-shrub-herb,shrub-herb and herb structure;2) 59 seedlings were detected in the regeneration layer of artificial vegetation in the central urban,only Podocarpus macrophyllus which is evergreen coniferous species was detected,24 evergreen broad-leaved seedlings belongs to 17 families were detected,and 34 deciduous broadleaf seedlings belongs to 23 families were detected. The number of seedlings in the regeneration layer of tree-shrub-herb structure was the most,and the number of seedlings in the regeneration layer of herb structure was the least;3) The occurrence frequency of seedlings in the regeneration layer of 4 community structures from high to low were tre-shrub-herb,tree-herb,shrub-herb, and herb community;4)The main seed dispersal pattern of seedlings in the regeneration layer were by birds and wind,and a few were anthropochory;5) Using PC-ORD software,CCA correlation analysis between species distribution under 4 community structures and the habitat factors which were investigated in spring and autumn,at the same time,using SPSS software to do significance analysis.The results indicated that the light intensity and the coverage of regeneration layer were the key limitation of natural restoration under artificial vegetation.The seedlings of the regeneration layer are classified into native plants and cultivars.Four types of native plants based on their position and function during the process of natural restoration,including pioneer species,serai species,climax species, associated species;cultivars can be divided into naturalize plants,garden variety,and Hypericum chinense.Based on the classification above,the artificial vegetation can recover to Topographic climax,and cannot recover to the zonal vegetation type in Shanghai.