Study On The Homogenization Of Urban Greening In The Yangtze River Basin

Urban area has now undergone severe biotic homogenization due to anthropogenic activities. The rapid urbanization around the world has led to the increase of non-native species and the decrease of local species, which finally causes the homogenization of species composition in global urban areas. The homogenization of species right now presents a significant challenge of biodiversity conservation. This study investigated the current status of biotic homogenization in 11 major Chinese cities along the Yangtze River based on both field study and literature review. Key findings of this study are summarized as follow:① A total of 679 landscape tree species, belonging to 289 genera and 88 families, was recorded. Within the 679 species, 198 were evergreen broad-leaved trees, with 210 being deciduous broad-leaved tree species, 128 being evergreen broad-leaved shrub species, and 143 being deciduous broad-leaved shrub species. Over 30 species were found in the Rosaceae, Magnoliaceae, Leguminosae, Cupressaceae, Lauraceae, and Ulmaceae family. Jaccard’s coefficient decreased with distance for the among-city comparisons of parks, roads and residential areas. But, similarity in landscape species composition did not correlate with distance for the among-city comparisons of campus greening.② Similarity in landscape tree species was significantly higher in northern subtropical(mean Jaccard’s coefficient: 0.532) cities than in middle subtropical(mean Jaccard’s coefficient: 0.382) cities(p<0.001).③ Among-city similarity in landscape tree species composition(mean Jaccard’s coefficient: 0.423) was higher than among-city similarity in natural vegetation(mean Jaccard’s coefficient: 0.133). As geographical distance increased, the similarity in natural vegetation decreased, with the similarity in landscape tree species composition decreased faster at the beginning but then remained unchanged.④ The among-city similarity in landscape tree species composition was all time higher than the similarity between landscape and natural vegetation.⑤ Following the downtown-suburb-countryside gradient, the similarity coefficients decreased from downtown to suburb and to countryside(mean Jaccard’s coefficient: 0.517,0.299,0.239).