Study On Characters Of Beach Vegetation And Its Succession In Dongting Lake Area

The main object of this research was the beach vegetation in Dongting lake area and the succession rule of the wetland vegetation in Dongting lake area was analyzed.The changes of integration polder Cultivated land between 1993 and 2004 were analyzed by taking a typical Cultivated land of East Dongting lake area as a research object.The landscape pattern and land use Cultivated land could be known after returning farmland to lake.The beach vegetation styles in Dongting lake area was investigated by the quadrat method and transect method.The investigated places were in four protected areas,East Dongting lake area,West Dongting lake area,South Dongting lake area and Hengling Lake area,a total of 20 spots constituted by 128 transects in number of 636 quadrats.All the transects are perpendicular to the land and water boundary,each transect included 4 to 6 quadrats with 1 to 2 meters' interval.The herd quadrat area is 1 by 1 meter.The plant species names,the number of trees,the average height of plants,the plant coverage,the biomass,etc.were recorded and the plant community composition,the relationship of plant community and its soil element and elevation were analyzed.The main research results were as follows:(1) There are 206 kinds of wild vascular plants in Dongting Lake area beach vegetation (including varieties) belonging to 53 families,128 genera.The main plants in the investigated community included Phragmites australis,Triarrhena lutarioriparia,Salix triandroides,Oenanthe javanica,Medicago polymorpha,Artemisia selengensis,Clematis terniflora var.mandshurica,Phalaris arundinacea,Carex brevicuspis and Juncus bufonius.(2) The plant communities substitution happened to be the elevation of river beach,and the plant had a significantly zonal distribution paralleled to the embankment.With the uplift of groundwater buried depth,the soil development deepened,and the surface and subsoil thickness increased.Soil types from low spot to high spot were bogginess meadow soil,meadow soil and alluvial soil,and the averaged specific gravity was higher up to 2.78 g/cm~3.The range of specific gravity was between 0.71g/cm~3 and 1.4g/cm~3 and the specific gravity increased according to the uplift of elevation,the distribution of total nitrogen content in the vertical direction was similar to the distribution of soil organic carbon.All the results show that the soil layer of total nitrogen content soil and organic carbon between 0 and 20cm is higher than the soil layer between 20 and 40cm.(3) The succession rule of Dongting lake area wetland affected by tectonic subsidence, sediment deposition,human activities was discussed,and the relationship between natural succession trajectory and formation causes of wetland of beach were analyze.According to all the research referred above,the result showed there were there formation causes of wetland of beach,namely of river deposition,lake deposition,and fluvio-lacustrine deposition,the succession rule of Dongting lake area wetland vegetation showed three succession rules.(4) After the farmland conversion to lake wetland,its background was changed from crops to poplars and the area of reed increased.The spatial structure of reed and dryland landscape became complicated because of the implementation of government policy about returning farmland to lake,while the spatial structure of forest establishment,young plantation,architecture landscape became much easier.After the returning farmland to lake, the integration polder changed from the small block,much landscape elements type to huge block,single type.According to the present research,the operation target and soil distribution section of all kinds of artificial vegetation can be designed according to the soil elevation distribution to form the best ecological-safety pattern which have the function of flood storage and also have a good economical and ecological benefit at the same time.The main problems of Dongting lake area wetland was analyzed according to the actual situation and suggestions of wetland restoration and protection aiming at these problems were given.