Cultural tree preference and its influence on tree biodiversity in urban public spaces in Nanjing city, China

Worldwide, various tree species have been worshiped and praised because they are culturally significant in many nations. To address the questions of whether and how the preference for cultural trees influences the plant diversity in urban ecosystems characterized by human-created vegetation, we surveyed the plant composition in 239 designed landscape units (DLUs). We compared the tree diversity in the DLUs with that in all public green spaces, including both natural remnants and cultivated vegetation, in the built-up area of Nanjing city, China. We found that the species richness proportion of native species decreased from 58.01 % (192/311) in all public spaces to 39.71 % (81/204) in the DLUs, largely due to the low species resource utilization ratio of native noncultural species, which accounted for 75 % of all native tree species. In detail, 77.08 % (37/48 species) of native cultural species and all introduced cultural species (57/57) were recorded in the DLUs; however, only 30.56 % (44/144 species) of native noncultural and 80.49 % (66/82) of introduced noncultural species in all public spaces were recorded in the DLUs. For the native trees that were recorded in the DLUs, the total frequency, total abundance, median abundance and median frequency of native noncultural species were much lower than those of the native cultural tree species, although the species richness of noncultural trees (44 species) was higher than that of cultural trees (37 species). Furthermore, the relative richness and abundance per DLU of native noncultural tree species were significantly lower than those of native cultural tree species (p < 0.05). The results indicated that the preference for cultural trees contributed to the low diversity of native trees in the DLUs. We suggest that the difference between 'national' plants in the cultural sense and 'native' plants in terms of their natural distributions should be discerned, especially in regions with unified cultures. Promoting regional cultural diversity and accepting the value of 'localized tree species' can help us coordinate the cultural value and native biodiversity value of landscaping trees in urban greening.