Street green spaces can effectively attenuate traffic noise, but the crucial role of coniferous trees and shrubs in the reduction in green space noise has not been systematically explored. Therefore, in this study, the aim was to determine the mechanism of the influence of plant morphological characteristics and planting forms on the noise reduction effect using field measurements of the noise reduction effect of 36 street green spaces planted with coniferous trees and shrubs. It was found that for the same width of street green spaces, the noise reduction effects of planting single and multiple trees were significantly different, and this difference increased with an increase in street green space width. The noise reduction effect of planting low shrubs in street green spaces was significantly different from that of planting common shrubs of the same width, and their difference increased with an increase in the street green space width. The factors that significantly affected the noise reduction effect of the 5 m wide street green space were tree height, crown width, and DBH, and all of them were positively correlated. In addition, the noise reduction effect of the street green space planted with conifers was affected by the road and pavement widths. Finally, in this study, a stepwise regression model was constructed for the noise reduction effect of street green spaces based on plant morphological parameters, planting methods, and physical characteristics of the road to quantify the crucial role of each factor in the noise reduction effect of street green spaces. The results of this study can provide plant noise reduction strategies for urban landscape planning and design to create a healthy urban acoustic environment.
