Terrestrial Vascular Plant Diversity And Vegetation Characteristics On Chongming Islands,Shanghai

With the rapid urban development in recent decades,urbanization has greatly changed the original urban ecological landscape pattern and affected the composition and distribution of plant diversity.Chongming Island is the largest alluvial island in the world and the only area in Shanghai that is undergoing urbanization.Shanghai have put forward the goal of"Building Chongming world-class ecological island with the strength of the whole city"since 2017.Therefore,it is of great significance for plant diversity protection and ecological construction to clarify the composition and spatial distribution pattern of plant diversity and the degree of impact by land use in Chongming District.In this study,we investigated vascular plant flora and community at 351sampling grids in terrestrial Chongming District,Shanghai.Based on the survey results,the flora of vascular plants in terrestrial Chongming District was analyzed firstly.Secondly,the community types were divided by cluster analysis according to the community quadrat data,and a classification system of terrestrial vegetation in Chongming District was constructed,and the differences of species diversity among different Vegetation Formations were compared.Finally,through the interpretation of land use in the survey sample sites,the linear relationship between environmental heterogeneity(i.e.,land-uses quantity),and spontaneous plant(i.e.,weeds and seedlings of woody plants)species richness was discussed at different spatial grains.At the same time,the relative importance of urbanization degree(i.e.,impervious surface coverage)and environmental heterogeneity in explaining species richness were assessed by random forest model(RF).The main conclusions are as follows:(1)The flora of vascular plants in terrestrial Chongming District is diverse and strongly disturbed by human activities.In total,826 species from 514 genera and 146 families were recorded in this study,including 534 spontaneous plant species and 501 cultivated plant species,and 209 species are both spontaneous and cultivated plants.Among 79 exotic invasive plants,13cultivated plants introduced artificially were at risk of escape.In terms of family and genus composition,compared with the previous studies on the flora of Chongming District,the proportion of few-family increased significantly,dominated by few-family,single-family and single-genes,and the phenomenon of"legacy"was obvious.In terms of geographical composition,tropical families and temperate genera were dominant,with both temperate and tropical origins.(2)There are abundant types of terrestrial vegetation in Chongming District,and Cultivation Vegetation plays a dominant role.According to the origin of vegetation,the terrestrial vegetation in Chongming District can be divided into Natural Vegetation and Cultivation Vegetation.Based on the results of cluster analysis of 361 community quadrates,the classification principle of"community physiognomy-species composition-community structure"was applied,and referring to the classification system of"Vegetation of China"and"Vegegraphy of China",the Natural Vegetation was divided into 2 Vegetation Formation Classes,2 Vegetation Formation Subclasses,2 Vegetation Formation Groups,2 Vegetation Formations and 31 Dominance types(Alliance);the Cultivation Vegetation was divided into 3 Vegetation Formation Classes,7 Vegetation Formation Subclasses,12 Vegetation Formation Groups,15 Vegetation Formations and 107Dominance types(Alliance).The Dominance type of Cultivation Vegetation accounts for 77.5%of the whole classification system.(3)The species diversity of Vegetation Formations were significantly different in Chongming District,which the species diversity of Natural Vegetation was higher.In forest vegetation,the species richness(S)of Deciduous Needleleaf Ecological Landscape Forest was significantly higher than that of Deciduous Broadleaf Orchard(p<0.05),but there were no significant differences in Shannon-Wiener Index(H),Simpson's Diversity Index(D)and Pielou's Evenness Index(J)among the seven forest vegetation types.In shrub vegetation,the four indexes of Deciduous Broadleaf Ecological Landscape Shrubland were significantly higher than those of Evergreen Broadleaf Ecological Landscape Shrubland(p<0.05).In herbaceous vegetation,the H,D and J indexes of Subtropical Secondary Grassland were significantly higher than those of Cash Crop,while the S index was significantly higher than that of Lawn(p<0.05).(4)There was a significant positive linear correlation between land-uses quantity and spontaneous plant species richness.Especially in small grain size(50×50 m),its explanatory power is the highest(p<0.001,R~2=0.31).The random forest model(RF)showed that the land-uses quantity contributed more to species richness than the impervious surface coverage,and the model also performed best at small grain size,explaining 52.3%of the variation in species richness.The above results all play an important role in small grain size,and with the increase of grain size,this influence began to decline gradually.In conclusion,the vascular plants in terrestrial Chongming District cover 27.7%of the total species in Shanghai,and the terrestrial vegetation includes the common vegetation types in Shanghai except the remnant vegetation.The urbanization degree and environmental heterogeneity jointly determine the species diversity of urban indicator organisms,i.e.spontaneous plants.Therefore,in the construction of Chongming Ecological Island,we should not only consider creating sufficient artificial green space,but also give full play to the role of Natural Vegetation and various land use types in providing habitat,so as to effectively protect the species diversity of wild plants in the terrestrial area.