Species diversity of Rhododendron shrub communities and utilization of Rhododendron resources in urban green spaces of Nanjing

As a traditional ornamental flower, rhododendrons are increasingly used in landscaping and urban greening. In this study, we surveyed 49 urban green areas and 134 sample sites in Nanjing, China, according to the functional type and administrative area of each green area using typical sampling and quadrat methods. We calculated the Rhododendron shrub community quantitative characteristics index and community diversity index to evaluate the species diversity of each Rhododendron shrub community. Additionally, the indicators of rhododendron planting in each sample site were counted to understand the characteristics of the application of rhododendrons in Nanjing’s urban green space and to identify the problems. According to the Simpson index and Shannon–Wiener index of the Rhododendron shrub community, road green space and Xuanwu District have relatively higher species diversity, while the Pielou index indicates that road green space and Jianye District have relatively higher species evenness. A total of 11 Rhododendron cultivars were found in this survey, among which R. simsii ‘ZiHuDie’ was the most widely used cultivar in Nanjing urban greenery; however, this result shows that the applied Rhododendron cultivars are too homogeneous. This study highlights problems affecting Nanjing urban greening and can be used as a reference for future Rhododendron breeding research.