Plant Diversity And Community Types Of Urban Green Space On Urban-rural Gradient In Harbin

In the past 20 years,China's urbanization is in the rapid development stage.The spatial distribution and attributes of urban green space have changed greatly.The original natural vegetation has gradually disappeared.At the same time,a large number of cultivation vegetation has become the main body of urban green space.Analyzing the response of plant diversity and community composition of urban green space to urbanization and its impact mechanism can provide a scientific basis for the ecological construction of urban green space.Therefore,in this study,the main urban area of Harbin was taken as the research area,and the flora and community of urban green space were investigated on the urban-rural gradient.Firstly,the floristic composition of urban green space was analyzed to clarify the plant diversity of urban green space in Harbin.On this basis,based on the sample survey data,cluster analysis was conducted and community types were divided to construct the classification system of urban green space vegetation in Harbin.Secondly,combined with the proportion of urban construction land area and three-dimensional volume characteristic factors of buildings,the impact of urbanization on green space was analyzed.Finally,by comparing the type and composition differences of plant communities in urban and rural gradient,the effects of urbanization on the differentiation and diversity of plant communities in urban green space were explored.The main conclusions are as follows:(1)Urbanization has profoundly changed the plant diversity of urban green space.A total of 470 species of vascular plants belonging to 301 genera and 92 families were recorded in this study,including 124 woody plants and 346 herbaceous plants.Compared with 611 herbaceous plants recorded in 1955,265 species were reduced.A few large families(such as Compositae,Poaceae,Fabaceae of herbaceous plants and Rosaceae of woody plants)account for 43% of the total species,while single specie genera and few species genera account for 89.1% of the total species,showing a highly differentiated pattern.In terms of geographical composition,temperate genera and species were dominant(> 85%),which is consistent with the climate of Harbin.In terms of plant sources,native species were the main source(> 88%).(2)There are various types of vegetation in urban green space,and cultivation vegetation plays a dominant role.According to the intensity of human disturbance,urban vegetation was divided into two categories: natural secondary vegetation and cultivation vegetation.Based on the classification principle of "phytocoenologyecology" and referring to the definition of classification units in Vegegraphy of China,a six level classification system of "intensity of human disturbance-vegetation formation group-vegetation formation-alliance group-alliance-community" was established.On this basis,387 quadrats were classified quantitatively by cluster analysis;natural secondary vegetation can be divided into 1 vegetation formation group,2 vegetation formations,5 alliance groups and 25 alliances;cultivation vegetation can be divided into 3 vegetation formation groups,6 vegetation formations,21 alliance groups and 37 alliances.(3)Urban expansion in horizontal and vertical space has an impact on plant species richness of green space.The relationship between species richness and patch area,distance from urban center,impervious rate,total building volume and coefficient of variation of building volume was analyzed by using generalized linear model.It was found that total species richness(TR),cultivated plant richness(PR)and spontaneous plant richness(SR)increased with patch area and its spatial distribution;TR and SR decrease with the increase of the impervious rate around the patch;TR,PR and SR increase with the increase of the total building volume around the patch;within the range of 500 m around the patch,the greater the coefficient of variation of building volume,the smaller the SR,and the greater the PR.In addition,TR and PR were positively correlated with the woody layer coverage of green patches.(4)The composition and diversity of plant community in urban green space are significantly different in urban and rural gradient.The proportion of construction land in urban central district(R1)was the highest(94.2%),and the community type was the lowest(23.0%);the proportion of construction land in urban inner district(R2)was the highest(89.0%),and there were urban forest and many urban parks,and the community type was higher(35.1%);the proportion of construction land in urban fringe district(R3)was the lowest(46.7%),and there were many large parks,green space and scenic areas,and the number of community types was the largest,accounting for 48.0%.The species richness,Shannon Wiener index and Simpson index of woody plant community were the highest in R2,and the related diversity index of herbaceous plant community was the highest in R3.To sum up,urbanization has profoundly changed the plant diversity and community types of green space in the main urban area of Harbin.The plant species richness of green space patches in this study is affected by its area size and location,the proportion of construction land in the surrounding areas and the three-dimensional buildings volume characteristics.Though there are abundant types of cultivation communities in areas with high degree of urbanization,there are few types of spontaneous communities and low species diversity.Therefore,in the planning and construction of urban green space,we need to improve its ecological service function from the perspective of local biodiversity conservation.