Study on the selection of key tree species for urban greening in China based on ancient tree distribution density: A case study of five major cities（Beijing, Shanghai, Guangzhou, Shenzhen and Hangzhou）

Ancient trees serve as important carriers of urban ecological and cultural heritage, and their distribution characteristics provide a scientific basis for the selection of greening tree species. This study takes five major cities （Beijing, Shanghai, Guangzhou, Shenzhen, and Hangzhou） as examples, analyzing the distribution density of ancient trees to explore strategies for selecting key urban greening species. By integrating data on the species, quantity, and density of ancient trees in each city, along with the current application status and growth characteristics of these species, a tree selection framework centered on ancient tree density was proposed. The findings indicate that high- and medium-density ancient tree species （e.g., P. orientalis in Beijing and F. microcarpa in Guangzhou） exhibit strong local adaptability and longevity, making them ideal candidates as framework or backbone species. Non-long-lived species among low-density ancient trees can be reasonably utilized within their natural lifecycles, while long-lived but sparsely distributed species require cautious application. The study also highlights issues in current urban greening practices, such as over-reliance on fast-growing species and neglect of ecological functions, and proposes optimization measures including the "three-thirds ratio" principle （no single species, exotic species, or fast-growing species exceeding 30%）, emphasis on regional characteristics, and the establishment of dynamic monitoring mechanisms. This research provides data-driven guidance for the scientific selection of urban greening tree species and lays the foundation for cultivating future ancient tree resources.