Similarity of ornamental plant composition in new residential areas in Yangtze River delta

Natural vegetation is homogenized to some extent under the effects of urbanization. Whether the planted vegetation also has the same problem is an issue to be concerned with. By using Jaccard Index (JI), the similarity of ornamental plant composition in 45 new residential areas of 10 cities in Yangtze River delta was investigated at the scales of residential area, city, and province. It was found that this similarity increased significantly along the gradient of residential area - city - province, with the JI being 0. 45 and 0. 50 at the scales of city and province, respectively, but decreased with increasing distance among cities. Owing to the small amounts, native plant species didn' t decrease the similarity among cities, but increased the similarity among provinces. These findings suggested that the ornamental plants in residential areas in Yangtze River delta were poor in species richness, especially of native plants, and presented homogenization trend.