Effects Of Urbanization On Plant Diversity

With the rapid process of urbanization in China,the contradiction between urban development and ecological environment has become more conspicuous.Numerous studies on urban biodiversity have shown that urbanization is one of the main reasons for biodiversity change.Currently,most research on urban biodiversity have noticed the effects of the external environment on biodiversity.However,for the demand of research purposes,research methods remained distinct in various cities.In addition,previous studies have primarily focused on assessing species diversity and less emphasis on the role of functional diversity and phylogenetic diversity.In this thesis,based on field investigations of communities in urban areas of Haikou in Hainan province,we quantified the impact of different ways to delimit study areas on the assessment of biodiversity of urban areas.Secondly,driving effects on biodiversity(including species diversity,functional diversity,phylogenetic diversity)by level of urban development,land use types and management modes were assessed.Thirdly,the correlations among different facets of biodiversity and applicability of biodiversity indices in urban environment were probed.The main results are as follows:1.Investigation on the species diversity were conducted in the urban area of Haikou twice using the same sampling protocol but two commonly used delimitations of the urban area(built-up area and master plan of the city).The two surveys produced significantly different estimates of plant diversity of the urban area,as the result illustrates.We concluded that the assessment of biodiversity can be affected significantly by how the boundary of an urban area is defined.Caution should be taken when comparing plant diversity in urban area reported in different studies,including species diversity,functional diversity,phylogenetic diversity.2.A total of 770 species belonging to 502 genera and 143 families were recorded in the built-up area of Haikou,including 229 tree species,238 shrub species and 303 herbaceous species.Among them,there are 398 native species and 372 exotic species,respectively.The principal families are Euphorbiaceae,Arecaceae,Gramineae,Myrtaceae,Leguminosae,and so on.The dominant species are Cocos nucifera L.,Pterocarpus indicus Willd.,Roystonea regia(Kunth)O.F.Cook,Ficus benjamina L.,Ficus microcarpa L.f.,Khaya senegalensis(Desv.)A.Juss.,Ficus microcarpa'GoldenLeaves',Ixora chinensis Lam.,Dypsis lutescens(H.Wendl.)Beentje&J.Dransf.,Hibiscus rosa-sinensis L.,and so on.Spatial distribution of urban forest is relatively single in Haikou city.And tree stratum level is low.The construction of urban forest is still in the early stage.Species survival rate is the important guarantee of sustainable urban plant community structure.3.There are significant correlation between the diversity index on a single angle in urban environment.There is also a significant correlation between species diversity and functional diversity.Significant correlation between phylogenetic diversity index and the other diversity indices of two angles is less.Decoupling phenomenon between functional diversity and phylogenetic diversity are related to the function indicators.Whether two indices are relevant are determined by the levels of consistency of species richness,which is illustrated in the index formula.Therefore,selecting the appropriate index system is an important prerequisite for proper understanding of urban plant diversity.4.In the same definition standards of urban area and sampling methods,there is little difference between urban species richness of city with similar cultural backgrounds and geographical proximity.However,plant species composition is strongly influenced by different urban development level.The city with higher level of development has higher proportion of exotic species.Urban development level have little effect on the plant diversity of tree layer,but make significant difference of plant diversity in shrub layer and herb layer.Therefore,the most obvious change is the plant species composition in a city development process.But the species diversity,function and phylogenetic diversity are in a relatively stable state in shorter urban development process.5.Plant diversity presents significant differences in different interference intensity and ways.Land use types of stronger disturbance always lead to higher species diversity and functional diversity,but the phylogenetic diversity do not have the corresponding change.In addition,land use have different degrees effect on plant diversity of different life types.For instance,transportation land has low species and functional diversity,and vacant has high species and functions diversity in herb layer.6.Different business model can still cause difference of plant diversity,which because of the consideration of the economic benefits and the demand for services.The functional richness of shrub layer in golf courts is lower than that in comprehensive parks,however its species richness is normally higher than comprehensive parks.Differences of Species morphological is the main cause of the contrast.And the usage of demand of shurb layer in golf courts is normally so simple that tree species were mainly used to make up from the landscape's point of view.The ratio of exotic species number and abundance are higher in the comprehensive parks than in the golf courses.Improving species and abundance of native species in comprehensive park is a important measures to reflect the local park features and reduce the maintenance cost for plant community.This study not only enrich the theoretical basis of the pattern of urban plant diversity,but also to improve the research framework of urban plant diversity.It also provides scientific and technological support for plant diversity protection and development.