The Diversity Distribution Pattern of Ruderal Community under the Rapid Urbanization in Hangzhou, East China

The process of rapid urbanization has affected the composition and diversity of urban vegetation species. The process of urbanization from 2000 was analyzed in the area of "one major city with three vice cities and six groups", according to the urban master planning of Hangzhou from 2001 to 2020. The results show that dramatic changes have occurred for land use types during the ten years from 2000 to 2010 in Hangzhou, of which urban land has become the main type of land use and the area of arable land has presented serious loss. This study found that the Gramineae and Compositae species were the main groups of ruderals in 1665 quadrats, which reflected the characteristics of a few large families. The number of Monotypic and Oligotypic family/genera accounted for 67.3% of the total number of families and 97.5% of the total number of genera. The ruderals were dominated by annual life forms with strong adaptability and high plasticity. The ruderal communities in the study areas were divided into 125 community types based on clustering analysis of the dominance of ruderal species. The proportion of summer annual ruderals in the dominant species of ruderal communities gradually decreased along the group-vice city-major city gradient. The percentage of winter annual ruderals was the highest and the percentage of perennials was the lowest in the groups. The number of ruderal community types showed a nonlinear decreasing trend along the urbanization gradient of the group-vice city-major city. The number of ruderal communities in the vice cities and the groups was similar, which was higher than that in the major city. Only species that are highly tolerant to urban habitats can be distributed under frequent and high-intensity human disturbances in the major city. Therefore, the number of ruderal communities in the major city was minimal and it had low diversity.