Response Of Natural Habitat And Plant Community Characteristics Of Urban Mountains To Urban Matrix

With the rapid development of urbanization,a large number of Karst cone-shaped or tower-shaped isolated peaks and hoodoos are surrounded by human-dominated urban matrix in the process of urban expansion in Karst areas,forming urban remnant mountain habitats,which are important resources of urban native plant diversity in this area.Although the study on urban plant diversity has been extensive,the study on the plant diversity of the residual habitats,especially those based on the remnant mountains,is very weak.What is the influence of urban matrix characteristics on plant diversity of urban mountain remains? The overall level and which level(tree layer,shrub layer,herb layer)of plant diversity are sensitive to the influence of urban matrix? Are these effects scale dependent? Do the different sizes of the urban remnant mountains behave differently? Remains unclear.Therefore,a total of 25 large,medium and small mountain sites in the study area were selected to calculate the alpha-diversity of plants at four levels: tree,shrub,grass and whole.Urban matrix indexes such as total impervious surface area,land use,vegetation coverage and fragmentation index were selected for measurement.Pearson correlation analysis and linear regression model were used to study the correlation and influence degree between plant diversity index and urban matrix index of urban mountain on 2000 m spatial scale.The results showed that:(1)The dynamic evolution of urban spatial pattern in Guiyang is complex.The spatial and temporal pattern evolution of the quantity structure and morphological characteristics of mountain patches in Guiyang is closely related to the process and stage of urbanization development.From 1988 to 2018,the increased number and area of mountain remains and the disappeared number and area of mountain remains increased with the expansion of built-up areas,but the peak periods were different with different stages of urban development.On the whole,the distribution of mountain remains of different cities in Guiyang is extremely uneven,the mountain remains of medium and small cities are mostly located in the middle of each city,and the mountain remains of large cities are mostly located in the boundary of each city.In addition,in the six periods from 1988 to 2018,the mountain remains of medium and small cities with simple plane shape,relative height of less than 50 m and average slope of less than 14° were dominant in quantity.With the large-scale transformation of urban landscape pattern and land use type in Guiyang built-up area,The shape of mountain patches in large cities became more complex,and the relative height and average slope gradually decreased.The shape of mountain patches in medium and small cities tended to be simple and regular,and the area gradually decreased,and the integrity of mountain patches in cities decreased.(2)A total of 724 species belonging to 548 genera and 168 families were recorded in this study.There were 434 native species and 290 alien species,respectively.The number,distribution range and growth space occupied by a small number of exotic species were significantly higher than that of native plants in the remaining mountains of the three cities.The species richness of all levels of the mountain remains of the three scale cities showed a trend of herb > shrub>trees> liana there were significant differences in the species richness of the tree and shrub layers of the mountain remains of the three scale cities,while there was no significant difference in herb and vine.The structural integrity of the mountain plant communities in small cities was higher than that in large and medium-sized cities,and the vertical structure of the mountain plant communities in three large cities was dominated by a four-layer composite structure of tree-shrub-herb-liana,and the diameter class structure of the trees showed an L distribution pattern.The overall plant diversity and plant diversity at different levels of the mountain remains in large cities were significantly lower than those in medium and small cities.The distribution characteristics of plant community species diversity on different slope directions were obviously different between different urban mountain remains of different scale and the same urban mountain remains of the same scale.There was no significant correlation between patch shape characteristics and plant community species diversity in urban mountain remains.(3)There were significant differences in the spatial scale range and correlation between the overall plant diversity and the plant diversity at different levels in response to the substrate characteristics,and there was no consistent rule.On the whole,the mountain remains and plant diversity at different levels in cities of different sizes were more affected by the structure,composition and urbanization process of the surrounding cities,and had no significant correlation with the indirect factors such as location and disturbance time.According to the linear loop simulation results,there is no single city matrix characteristic index and spatial scale that can well explain the overall pattern of mountain remains and plant species diversity at different levels in cities of different sizes.There was no significant correlation between the overall plant diversity and impervious surface area at the spatial scale of 2000 m,but they were all affected by the synergistic effects of land use,fragmentation degree and vegetation coverage.There was a significant linear relationship between plant diversity and urban matrix at different levels of mountain remains in cities of different sizes.The residual mountain tree layer in large cities and the residual mountain shrub layer in medium and small cities were affected by dual factors and had a significant linear relationship.The remaining mountain shrub layer in large cities was only affected by a single factor.The diversity of trees,shrubs and herbaceous layers in small cities,herbaceous layers in large cities and herbaceous layers in medium-sized cities was more sensitive to the urban matrix,all of them were influenced by the superposition and synergistic effect of multiple urban matrix factors.It is because of the high heterogeneity and connectivity of the urban matrix environment that the increase of intense human activities leads to the increase of alien species,which leads to the positive influence of some urban matrix factors on the plant diversity of urban mountain remains.