Study On The Spatial Pattern Of Urban Plant Diversity And Its Drivers In Zhanjiang,a Tropical Coastal City

Plant diversity is a fundamental feature of urban green space and it plays an important role in supplying ecosystem services and improving city people’s well-being.If we can regulate and predict the urban plant diversity in future,that will be helpful for the sustainable development of urban ecosystem.However,the regulation and prediction of urban plant diversity were based on understanding it and its drivers.Zhanjiang is located in the southernmost of Chinese mainland,which is the north edge of tropical area.It is the central city of western Guangdong Province and is undergoing rapid urbanization.In this paper,we studied the urban green space in Zhanjiang.We adopted stratified random sampling to set up our filed plots.We set up a total of 260 plots based on the urban functional units(UFUs).During our field study,we surveyed 521 tree plots,1926 shrub plots,and 3115 herb plots;in addition,we collected the information about the construction age,UFU type,population density,land value and green space maintenance frequency at each UFU;and collected soil sample at each tree plot to measure soil physio-chemical properties.The area,perimeter,land cover and green space landscape indices of each UFU were obtained by satellite image interpretation.Regression analysis was used to explore the relationship between the plant diversity and the characteristics of each UFU.ANOVA was used to compare the differences of plant diversity in different UFUs.The main conclusions were as follows:(1)The diversity pattern of spontaneous plants and its drivers: At Zhanjiang spontaneous plants were mainly herbs.The diversity of spontaneous plants were highest at urban village and wasteland,lowest at transportation area;the phylogenetic structure of spontaneous plants was clustered than cultivated plants.The species richness of spontaneous plants were influenced by both human management activities and habitat conditions.The urban village and wasteland with lowest green space maintenance frequency has highest spontaneous species richness.The transportation area with harsh habitat only has few spontaneous species.Soil organic matter and water content had weakly negative effects on species richness and phylogenetic diversity of spontaneous plants,respectively.The clustering phylogenetic structure showed that spontaneous plants were closely related and many of them were from Poaceae,Asteraceae and Fabaceae.(2)The diversity pattern of cultivated plants and its drivers: Species richness of cultivated plants was highest in commercial residential and parks,and lowest in wastelands.The species richness of cultivated plants was associated with the function of UFUs.As the main function of commercial residential areas and parks are improving the living environment of urban residents,so they always have higher plant diversity.Soil physical and chemical properties had no significant effect on the diversity of cultivated plants.The phylogenetic structure of cultivated plants was clustered.Compared to spontaneous plants,the phylogenetic diversity of cultivated plants is higher and the phylogenetic structure is more diverse.This suggests human preference played a dominant role in the diversity of urban plants.However,the taxonomic diversity was decoupled with phylogenetic diversity in urban area.(3)The tree structure and diversity: The tree diversity was high at Zhanjiang,including51 families 137 genera 185 species.Tree species richness was significantly positively correlated with Shannon Wiener index(He),but weakly correlated with evenness index(Je).The species richness and He of tree was higher at commercial residential areas,parks and institutions.Je was higher in all UFUs except forest lands.The most abundant tree families in Zhanjiang were Fabaceae,Arecaceae,Moraceae and Myrtaceae which also has the largest number of individuals.The species richness of exotic trees was slightly lower than that of native trees,but the individual number was far more than that of native trees.This showed the dominance of exotic trees in Zhanjiang urban green space.The tree with the highest importance value was Ficus microphylla L.f.The trees with large importance value were always had good appearance and environmental adaptability,which reflected the human preference for cultivated plants.(4)The DBH(Diameter Breast Height)structure of trees and its drivers: In this study,a total of 12,434 trees were investigated.Most of trees with DBH between 5 to 15 cm,which showed that the trees in Zhanjiang City was young.Among the top 33 trees with the largest DBH,20 were Ficus plants,indicating that Ficus is a traditional greening species in this city.The average DBH of the trees was the largest in commercial areas and urban villages.The tree DBH in Zhanjiang was positively associated with the construction age and impervious surface rate of UFUs,but negatively associated with greening surface rate.(5)Green space landscape pattern and its drivers,and the effect of green space landscape pattern on plant diversity: The species richness of spontaneous and cultivated plants in Zhanjiang was positively affected by patch numbers,which indicated that the more fragmented the landscape,the higher the species richness was.The landscape pattern of green space nearly had no effect on phylogenetic diversity of both plants.The types of UFUs,construction age and population density had significant effects on green space landscape indices.The green space was more fragmented at old UFUs,but larger and more connected at new UFUs.Based on UFUs,this study revealed the diversity pattern and its drivers in Zhanjiang,a tropical coastal city.It was a new important case for the study of urban plant diversity.And it was a good guideline for the urban green space planning and management at Zhanjiang.