Study On Habitat Fragmentation And Its Impacts On Biodiversity At Urban Areas

Habitat fragmentation is the major cause of the low biodiversity level in city area.Based on ecological theory and method as well as remote sensing and GIS software,this paper made research on the present situation of biodiversity and habitat fragmentation of Suzhou as well as the structure of eco-system and the landscape pattern in this area,the evolution of landscape pattern in the last two decades and its driving force are also discussed and a biodiversity protection plan is made in this paper.The research result is helpful on revealing the reason of landscape pattern evolution and biodiversity change in city area caused by urbanization,and can also provide a new theoretical base in the biodiversity protection and plan.The major result of this research is listed below:1.Species list of plants,avian,fish and amphibiansThrough a two-year investigation,the species list of plants,avian,fish and amphibians is completed.Plants which belong to 134 families,400 genera and 623 species are found in the built-up area of Suzhou(674.6km~2),in which 466 species are local species.And plants which belong to 145 families,466 genera and 778 species are found in the city.area of Suzhou(1650km~2), inwhich 616 species are local species.The indexes of local plant are 0.75 and 0.79.The 151 tropical elements contribute to 39.02%and The 236 temperate elements contribute to 60.98%at genera level of the flora.The temperate element is the majority so this area is in the south edge of the north subtropical zone.The major invasion plants are Solidago Canadensis,Ambrosia artemisitifolia,Alternanthera philoxeroides and Eichhornia crassipes.The most common road greening tree species such as Cinnamomum camphora,Platanus acerifolia,Loropetalum chinense, Buxus microphylla,Sabina chinensis cv.Kaizuka and Rhododendron pulchrum are used over the frequency of 20%in the build-up area,Cinnamomum camphora is even used in the frequency of over 70%,so the richness of biodiversity in road greening system is low in the tree layer.And the trees found in nature communities such as Castanopsis sclerophylla,Cyclobalanopsis glauca, Phoebe sheareri,Schima superba,Ilex chinensis,Celtis sinensis,Acer buergerianum,Melia azedarach,Tilia queliana,Albizzia kalkora and Quercus spp are the potential choices of the road greening system.The common community types are listed below:①Evergreen broad-leaved forest:Castanopsis sclerophylla community,Phoebe sheareri community and Schima superba community.②Deciduous broadleaved forest:Quercus variabilis community,Liquidambar formosana community,Platycarya strobilacea community③Coniferous and broadleaved mixed forest:Pinus massoniana+Liquidambar formosana community④Coniferous forest:Pinus massoniana community,Pinus elliottii community,Cunninghamia lanceolata community⑤Secondary Shrub:Coriaria nepalensis+Vaccinium bracteatum community,Coriaria nepalensis +Phyllostachys nidularia community⑥Aquatic vegetation:Phragmites communis community,Hemarthria sibirica community⑦field community.203 species of birds belong to 12 orders and 44 families are recorded in the investigation,in which 125 species of birds are found in the build-up area.There are 3 types of the first class national protect birds,which are Ciconia nigr,Ciconia ciconia and Mergus squamatus,30 types of the second class national protect birds.There are 19 species of birds are found in Suzhou for the first time based on the record.The bird biodiversity of Suzhou city and the build-up area are 3.45 and 3.12.48 species of fish belong to 7 orders,15 families and 38 genera are recorded.According to reference,107 species existed in the Taihu Lake.Because of the use of sluice,reclaimiation, excess fishing and environmental pollution,many species especially migration fishes have been extinct for several years such as Acipenser sinenis,Trachidermus fasciatus,Takifugu obscurus, Myxocyprinus asiaticus and Leiocassis longirostris.This is the first Comprehensive investigation of species in Suzhou.2.Caculate the habitat fragmentation index and its temporal variationBase on ERDAS IMAGE and ARC/INFO software,this paper analyzed the landsat image of year 1987,1995,2001 and 2005.The habitat fragmentation indexes of Suzhou in these 4 years are 0.2854,0.2901,0.3012 and 0.3404.3.Analyse the effect of habitat fragmentation on biodiversityEffect on plant community:Based on the analysis of the richness of species of 9 types of communities,the richness of species decreased as the naturalness of the community increased from herbaceous plant community to plantation community to natural-forest community.And in natural-forest community,the richness index rises through Secondary Shrub to Deciduous forest to evergreen forest.Because of the effect of relaxation in plantation community,the richness of species is higher than that in the natural-forest community.Effect on amphibian community:The habitat fragmentation index in 1980s-1990s are 0.285, but now 0.340,while the Shannon-winner index of amphibian decreased from 2.25 to 2.10.Effect on birds community:Through the analysis of the correlation between the birds amount and frequency in the 9 parks and the 12 structure indexes of the parks,we reach the conclusion that Passer rutilans and Turdus merula are mostly effected by the area of the habitat, while Carduelis spinus,Parus venustulus,Aegithalos concinnus,Anthus hodgson,Paradoxornis webbianus and Trachybaptus ruficollis are mostly effected by humanlnterference.The amount of Pycnonotus sinensis and Streptopelia chinensis has Significant Negative Correlation with the shape index of the habitat.The evolution of landscape pattern caused by habitat fragmentation:The habitat fragmentation index increased 16.2%from 1987 to 2005,the patch density increased 52.3%and the mean patch area decreased 86.1%.The fragmentation of Cultivated Land,green space and rural construction area increased Significantly while the index of urban construction area and wetland decreased.The shape index of the landscape level increased 23.1%during the 2 decades.Analyzed on the landscape class level during the 2 decades,the area of Cultivated Land decreased while the habitat fragmentation index increased the area of green space first decrease then increased,the habitat fragmentation index increased.The area and habitat fragmentation index of wetland both decreased.The area of urban construction area increased and the habitat fragmentation index first decreased then increased.4.Analyze the evolution of landscape pattern and the driving forceBased on the statistics of the social-economical data of Suzhou during 1987-2005,this paper choose 13 indexes in 4 major class for the Principal Component Analysis of the driving force of the evolution of landscape pattern.The result shows that the index of proportion of Non-agricultural population,GDP,Social Fixed Assets Investment and average net rural per capita income indexes have the major contribution to the evolution of landscape pattern.And Social Fixed Assets Investment index have the largest contribution.5.The guideline of biodiversity protection plan On aim of forming a complete and better working system for biodiversity protection,and building an ecological garden city with rich biodiversity,reasonable structure and sustainable development,this paper suggest a guideline of biodiversity protection plan.Based on the requirement of biodiversity protection,the city is classified into 5 major function areas:the forest bio-protection area,the wetland bio-protection area,parks,biological corridors and artificial ecosystem.Different protection methods are used in different function areas.