Analysis on changes of street tree structure in Beijing from 2010 to 2020

  Objective  By investigating the changing trend of street tree structure in Beijing from 2010 to 2020, the purpose of the research was to identify the main challenges and give references for street tree establishment and management in the future.

  Method  Typical sampling methods and the same sample plots were used to investigate every street tree within the Sixth Ring Road of Beijing in June to September from 2010 to 2020, respectively. The variations of ten years in street tree species composition, utilization frequency, crown diameter and species important value in Beijing were analyzed from different perspectives.

  Result  Six families, ten genera and eight species had been increased during the last ten years in Beijing, and all of them were occasional species. The proportion of arbor and shrub had also increased. The street trees are mainly native species and deciduous species, with a higher proportion of deciduous species. The total proportion of top ten street tree species ranking by utilization frequency had increased, and proportion of Fraxinus chinensis trees was the highest one, while the decrease in utilization frequency of Rosa xanthina was the highest one in recent decade. The important value of Sophora japonica was still much higher than other street tree species though it was decreased by 8.2%. The average crown diameter of street trees decreased by 0.1 m for massiveness of new planted trees. The proportion of street trees in the 1st and 5th crown diameter class had decreased. The top ten street tree species ranking by average crown diameter range had narrowed, and the Platanus acerifolia had been the most decreased species in the 1st crown diameter class.

  Conclusion  The tree species richness is increasing, but relatively sample tree species composition and higher proportion of single species are the main problems while could affect the stability of urban road vegetation ecosystem in Beijing. Therefore, the range of tree species selection should be broaden, mixed configuration with more broadleaved deciduous tree species, evergreen shrubs and herbs should be constructed. The cultivation and application of native species should be strengthened, while the high-value exotic tree species should be introduced appropriately. At the same time, we should also protect the tree crown structure to enhance the shading effect of street trees in the urban greening.