Species diversity of three major urban forest types in Guangzhou City, China

Abstract

Guangzhou city in South China was assessed to understand the associations between tree species diversity and urban development. The study area covers five urban districts which form the bulk of the built-up areas. Reconnaissance field trips and aerial photograph survey identified main green covers in three urban-forest types, namely roadside niches, urban parks, and institutional grounds. Trees at roadsides and 21 parks were censused, whereas 14 large institutional sites were sampled. A total of 115,140 trees were evaluated for species identification, dimensions and site-environs conditions, with 40.8% at roadsides, 38.2% in parks, and 21.0% in institutional grounds. The urban forests composed of 254 species in 62 botanical families led by Moraceae, Caesalpiniaceae and Myrtaceae. Institutional forest has the highest diversity, followed by park and roadside trees. Most trees are derived from a small group of dominant species. Broadleaf species are prominent, especially the evergreen, whereas conifers and palms are sparingly adopted, except palms in institutional areas. Exotic species, mainly originating from tropical Asia and Australia, are common but not as dominating as in other tropical cities. Native species include spontaneous invasion into ruderal habitats, especially in parks. Species composition was interpreted vis-à-vis the interplay of natural and cultural factors then and now. Changing site conditions (geometric vs. physiological attributes), decision-making and management regimes (official-public vs. individual-lot stewardship), funding constraint (straitjacketed vs. adequate), intended amenity functions, and evolving landscape fashion (traditional vs. innovative), have helped to mould respective species assemblages to define their identity. Implications for long-term tree planning and management in Guangzhou and other fast developing cities are explored.