Optimization of Street Tree Species Based on Green Plot Ratio

Abstract

Street trees make up an important part of the eco-environment and landscape of urban roads. The species of street trees significantly affect the green volume of urban roads. The leaf area index (LAI) is often adopted to measure the ratio of green volume for urban roads, laying a scientific basis for optimizing street trees. This paper measures and analyses the LAI and green plot ratio (GPR) of 14 common street tree species in Xinxiang, a city in Central China’s Henan Province. The results show that, except for evergreens, the LAI values of deciduous trees varied significantly from month to month, forming a single-peaked curve. The LAI values of street trees have a significant positive correlation with the day of year (DOY) (P<0.01). As for the roads with a single row of street trees, the highest mean annual GPR values were achieved by Juglans regia Linn., followed in turn by Ligustrum lucidum Ait., Sophora japonica L., Populus tomentosa Carrière, Fraxinus chinensis Roxb. and Platanus orientalis Linn. Among the 12 common types of double-row road tree combinations, the GPR values all increased first and then decreased; the largest annual mean value belonged to the combination “Sophora japonica L.+ Sophora japonica L.” In the same section, the annual mean GPR value of double-row road trees was 3-7 times higher than that of single-row road trees. Our research demonstrates that the GPR can quantify the differences between different street tree species and combination types, and help to optimize the greening arrangement and plant configuration.