A Study On Urban Tree Species Diversity Assessment And Species Planning In China

Urban forests are an important part of the urban ecosystem.They can generate ecosystem services that are critical to the health and well-being of urban residents.Tree species diversity is one of the key factors that affect the sustainable supply of ecosystem services by a urban forest and its sustainability.Increasing the number of species used in urban greening programs can increase the tree species diversity in a city.However,improper tree species selection cannot only lead to low ecological benefits but also economic losses and waste of resources.Therefore,it is of great scientific and practical significance to fully understand the diversity pattern and shaping forces of urban tree specie diversity in China.Furthermore,to use the information to guide species planning that can improve the species diversity in a reasonable way.Based on data synthesized from literature and field surveys,the diversity pattern of urban tree species in 257 cities in China was analyzed in this study.Guided by principles proposed for urban tree species planning,tree species that are potentially usable in the built-up areas of 338 cities at the perfecure level and above in China were planned by using tree species already planted in the city as the species pool.Beijing was then used as an example to demonstrate how to apply the planning result at a single city scale.Main findings of this study include:1.In the 257 cities,the average species richness of trees(including shrubs and liana)was 128±118.The total number of tree species was 2,640,of which nearly one-fifth were exotic species.The most common species were Sulix bahylonica L.,Juniperus chincnsis L.,Prunus cerasifera Ehrh.,and etc.The compositional similarity of urban trees among cities showed a latitudinal gradient.The dissimilarity of species composition between urban areas at the same latitude was low.In addition,biotic homogenization was observable as some tree species distriuted widely in different cities.Within cities,park was the land use type which had the highest species richness while open land had the lowest value.2.Guided by principles proposed for urban tree species planning—matching the climate,adapting to urban environments,and diversity of tree species—tree species planning was conducted for built-up areas in 338 cities at the prefecture level and above in China.The result showed that the average number of tree species that can be potentially used in greening in those cities was 705±323.Cities in the middle humid subtropic region had the greatest potential to increase their tree diversity,with 930±245 species that could be potentially used on average.Cities in the middle temperate arid region had the least potential to improve their tree diversity as only 187±105 tree species could be potentially used on average.3.According to the result of tree species planning,565 tree species could be potentially used in Beijing Among them,278 tree species have been found in an survey of the urban forest in Beijing.The rest 287 species were further planned by following the principle of matching traits of tree species with land use.After excluding 48 tree species with allergenic pollens or cotton seeds and 197 tree species whose allergenicity of pollens was unknown,39 tree species without allergenic pollens or cotton seeds and three species whose female trees could be used following the strictest planning principle.Among them,42 species could be used in parks and open lands and 14 species,13 species,3 species and 1 species could be used in commercial areas,residential areas,institutional areas and and street sides,respectively.4.Overall,tree species diversity in Chinese cities was comparable to that of their international counterparts.Nevertheless,there is a plenty of room to improve the species diversity of urban trees if considering the diversity of tree species naturally distributed in China.Based on the result of species planning from this study,every city had certain number of tree species that can be potentially used in future urban greening programs after trials.