Species Composition And Distribution Pattern Of The Weed Communities In Chongqing Metropolis

Weeds,as a special group in urban vegetation,have strong adaptability and high plasticity,and can respond to high-intensity human disturbances and heterogeneous habitats by changing their own forms and life history strategies.In the context of the continued degradation of urban biodiversity,weeds are important for the maintenance and conservation of urban biodiversity.We set up 86 1 km × 1 km vegetation surveying plots in Chongqing metropolis using the grid method,and investigated the species composition and distribution pattern of the weed communities in the context of rapid urbanization.In addition,the weed data of 32 cities in five climatic zones were collected through literature review.We analyzed the species composition,diversity pattern and community composition similarity,and evaluated the degree of homogenization of weed species.The results of this study are as follows:(1)301 weed species belonging to 223 genera and 69 families were recorded in Chongqing metropolis.Among the recorded species,species of the Compositae and Gramineae were the most abundant;annual weeds and dwarf weeds were the dominant types of weed species;the weed communities in Chongqing metropolis were mostly composed of native species,and there were 31 species and 11 species of exotic weeds and invasive weeds recorded in this study,respectively.(2)Along the urbanization gradient in Chongqing metropolis,the similarities in weed species composition in high-,medium-and low-urbanization areas were low.Additionally,the dominant species compositions of the weed communities in the different areas were different;urbanization impacted the weed biodiversity,evidencing by the lower number of weed species and Shannon-Wiener diversity index in the high urbanization areas than in the medium and low urbanization areas;the number of weed species in the 86 sample plots showed a polycentric pattern with the increasing of distance between the survey plot and city center.(3)Among the weed habitats in Chongqing metropolis,the soil abandoned land contains the largest number of weed species,while the forest gap and tree pool contain the least number of weed species;in the habitats of shrub space and tree pool,the number of weeds species decreased gradually from high urbanization area to low urbanization area,while the number of weed species in cultivated land and soil abandoned land increased gradually;in spring and autumn,there were large differences in species composition,similarity index,dominant species,sample species and Shannon-Wiener diversity index among different habitats in different urbanization areas.(4)1367 weeds belonging to 677 genera and 125 families were collected in 32 cities in this study.Among the recorded species,annual weeds and dwarf weeds were the dominant types of weed species,and the number of weed species in each city ranged from 80 to 301 species.Weed diversity was significantly negatively correlated with urban altitude and positively correlated with urban precipitation and population density(GAM-generalized additive models,p < 0.01).The Jaccard similarity index of urban weed species had a climatic band scale effect,the mid-subtropical similarity index was the highest,and the mid-temperate zone was the lowest.The composition of urban weed species was mainly affected by the geographical distance among cities and urban altitude and climatic factors,but was weakly affected by socioeconomic factors(population density and per capita GDP).