The Spatial Pattern Of Urban Plant Diversity And Its Influencing Factors In Shanghai,China

Urban plant diversity is imperative for maintaining ecosystem services and ecosystem functions thus for human well-being.Cities are regarded as biodiversity hotspots,which play important roles in the conservation of global biodiversity.However,rapid urbanization has become a serious threat to plant diversity,it greatly challenges the maintenance and protection of urban plant diversity.Urban ecosystems is a compound system composed by natural,social,and economic,it characterized by high landscape heterogeneity and multiple disturbance factors.Whether and how urban plant diversity is affected by urbanization process and attached ecological environmental factors remain unclear.This thesis aims at answering the following questions: How the plant diversity changes along the urban to rural gradient? And whether and how the urbanization degree,urban land use types and urban landscape pattern affect urban plant diversity? Plant diversity data of 260 sample sites sampled by double-density stratified random sampling method cover the entire continent of Shanghai were investigated.Landscape pattern data were calculated from land use/land cover data within 1 km around the sample sites,which were interpreted and digitalized from the high-resolution aerial image.This study quantitatively analyzed the distribution patterns of ? and ? diversity of different plant taxa along the urban-rural gradient using gradient analysis method.Statistical methods such as regression analysis,analysis of variance(ANOVA),non-metric multidimensional scaling analysis(NMDS),correlation analysis(Spearman),and robust regression tree analysis(BRT)were used to explore the underlying mechanisms of effect of urbanization(urbanization degree,urban land use and landscape pattern)on diversity of different plant taxa.Main results and conclusions are as follows:(1)653 vascular plants belong to 424 genera and 125 families were recorded in260 sample sites.The number of native plants is 261,of which the proportion of native spontaneous plant is 78.08%.The number of exotic plants is 392,of which the proportion of cultivated plant is 79.39% indicating that cultivated plants are an important part of urban flora.The distribution patterns of species richness of different plant taxa showed several models(e.g.peak,bimodal,monotonous increase or decrease,and random distribution)which indicate the anisotropic characteristic.Relative to suburban area,urban and rural areas found homogenization trend results from the peak trend of ? diversity along the urban-rural gradient.Exotic plants play a vital role in mitigating biotic homogenization by comparing the ? diversity of native plant and exotic plant along the urban-rural gradient.Exotic cultivated contributed most because of the diversity is higher than exotic spontaneous and exotic spontaneous plants promote biotic homogenization.The species turnover component contributed more to ? diversity than the nestedness resultant component.(2)The index that characterizes the urbanization degree shows linear and non-linear pattern along the urban to rural gradient,reflecting the spatial differentiation of urban development.In addition to native plants,the urbanization degree can significantly affect the species richness of other plant taxa including all plant,woody plant,annual herb,perennial herb and exotic plant species richness that exists some small difference because of scales and the relationship can be depicted by linear model and quadratic polynomial model.Only the ? diversity of woody plant between the samples was significantly affected by urbanization degree and the relationship can be depicted by linear model,while the ? diversity of other taxa were not.(3)Total number of plant species under different land use was: residential land(434)> agricultural land(425)> green land(401)> traffic land(343)> wasteland(281)> public facilities land(241).Except for woody and perennial herb,the species richness of total plant,annual herb,cultivated plant,spontaneous plant,native and exotic plant are all significantly affected by land use.Further,except for native plant,there is a significant difference between two or among several land use types.Non-metric multidimensional scaling results showed that species clustering were significant according to PERMANOVA test.However,there also exist an obvious overlap among land use types.The similarity of all plant and different taxa under different land use types were compared.The mean similarity of all plant between sample sites is0.20-0.26.The similarity of exotic plant(0.24-0.32)is lower than that native plant(0.17-0.25),the similarity of exotic cultivated is highest(0.32-0.41)and the exotic spontaneous plant is lowest(0.12-0.17).These results showed that Exotic plants play a vital role in mitigating biotic homogenization,of which exotic cultivated contributed most,while exotic spontaneous plants promote biotic homogenization.(4)The relationship between landscape pattern indices and native,exotic spontaneous plant is various by different landscape pattern indices and different species of origin.There is a significant positive correlation between the landscape diversity index and native,exotic spontaneous plant species richness,also showed a negative relationship with ? diversity between sample sites of native and exotic spontaneous plant.There is a significant positive correlation between landscape shape index and native,exotic spontaneous plant species richness,also and ? diversity between sample sites of native and exotic spontaneous plant.While the correlation between the percentage of green land,percentage of agricultural land and percentage of waste land and species richness of native and exotic spontaneous plant or ?diversity between sample sites of native and exotic spontaneous plant is different because of different scales.The joint effect of the landscape pattern indices on species richness and ? diversity is different at two scales.The relative contribution of urban landscape pattern index to the species richness of native spontaneous plant is:landscape diversity index> landscape shape index> land use.The relative contribution of urban landscape pattern index to the species richness of exotic spontaneous plant is:landscape diversity index > Land use > Landscape shape index > Percentage of waste land.For the ? diversity of native and exotic wild plants between samples,the relative contribution of landscape pattern index at the 0.5 km scale is Percentage of agricultural land > Percentage of green land > Percentage of waste land > landscape diversity index > landscape shape index,1 km scale is: percentage of agricultural land > percentage of waste land > landscape diversity index > landscape shape index.We found there exist a stronger effect of the past landscape pattern index on present species richness of all spontaneous herb including annual and perennial herb than current landscape pattern.This give an evidence of exist of time lag of the effect of landscape pattern on urban plant diversity.The aboved results can enrich theoretical basis for the distribution pattern of different taxa and driving force in urbanization process,which help well understand the mechanisms of urbanization on plant diversity.Further,it provides insight into the conservation and management of plant diversity to decision-makers in the future.