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Chinese Journal of Ecology ›› 2020, Vol. 39 ›› Issue (8): 2678-2690.

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Quantitative characteristics of roadside tree canopy cover under the background of urban expansion: A case study of Beijing.

ZHANG Wen1,2, LI Xiao-ting1, MA Jie1,3, JIA Bao-quan1*#br#   

  1. (1Research Institute of Forestry, Chinese Academy of Forestry, Key Laboratory of Tree Breeding and Cultivation, National Forestry and Grassland Administration, Urban Forest Research Center, National Forestry and Grassland Administration, Beijing 100091, China; 2East China Jiaotong University, Nanchang 330013, China; 3Henan Institute of Science and Technology, Xinxiang 453003, Henan, China).
  • Online:2020-08-10 Published:2021-02-10

Abstract: Roadside tree canopy (RTC) is the most important component of urban tree canopy (UTC). In this study, we constructed an evaluation system of RTC quantitative change from a perspective of the relationship between RTC quantitative change and urban expansion, which can provide basis for urban planning and road green space system management. Based on quantitative relationships between RTC and road, impervious surface, UTC and possible UTC (PUTC), we established five evaluation indices. The spatial distribution analysis and evaluation were carried out for regions between ring roads in the main urban area of Beijing. The results showed that the growth of RTC area was remarkable from 2002 to 2013, with a change index of the RTC area being 2.142, and the coverage rate increasing from 21.62% to 35.00%. The overall RTC growth showed obvious dominant response compared with the urban impervious surface change and the road weighting change. The overall I (impervious surface) response index was 1.879, and the R (road) response index was 1.736. The RTC showed weak dominant response compared with the overall growth of UTC and the decrease of potential UTC area, with overall U (UTC) response index of 1.055 and P (possible UTC) utilization index of 1.06. RTC area change index, I response index, R response index, and P utilization index all showed an increasing trend from inside to outside urban expansion. U response index was basically balanced between ring road areas, while the other indices had obvious differences. The difference of RTC area change index was the biggest between ring road areas. R response index showed the most significant correlation with RTC area change index. The RTC area changed greatly in urban outskirts, and its response advantage to road and urban impervious surface changes all showed a more significant trend from the inside to outside. New roads and impervious surfaces had higher RTC coverage. There was no correlation between U response index and RTC growth rate. The difference of RTC between ring roads in the main urban areas of Beijing was significant, with a promoted demand in the innercity, and especially the lagged demand inside the 2nd ring road which needed to be concerned. RTC position and tendency advantage in the overall urban tree canopy cover need to be strengthened, especially in regions inside the 3rd ring road. Leaving room for RTC growth was compressed. Exploring potentials of impervious surface in built-up areas is an important approach to RTC subsequent growth.

Key words: roadside tree canopy, urbanization, urban tree canopy, Beijing.