Objective The noise reduction effect of street green spaces is influenced temporally by changes in optical poropsity during leaf-shedding and spatially by the plant configuration structures. This study aims to reveal the spectral characteristics and spatiotemporal heterogeneity of noise reduction in street green spaces with different plant configurations under continuously varying optical porosity conditions.

Method Taking street greenery vegetation as the research subject, measurement points were established along the roadside and behind the green belt to collect sound pressure level data at different stages of leaf-fall (representing varying porosity) and to calculate the noise reduction effect. Through correlation analysis, factors influencing noise reduction during the dynamic leaf-shedding process were identified. Subsequently, a linear model was developed to relate noise reduction to the DBH and height of trees and shrubs.

Result (1) As traffic noise frequency increased, the noise reduction effect of street green spaces exhibited a trend of “fluctuation (< 200 Hz) - stabilization (200−2 000 Hz) - increase (> 2 000 Hz)”. Optical porosity has a more pronounced impact on the attenuation of high-frequency (> 2 000 Hz) traffic noise in our measurements. (2) The influence of porosity variation on noise reduction differed among plant configurations, with a general trend of decreasing noise reduction effectiveness as porosity increased. (3) The complexity of the vertical structure was relatively important for enhancing the noise reduction effect of street green spaces. Under low to medium porosity conditions, green spaces attenuated high-frequency noise more effectively than mid-to-low frequency noise. In contrast, under high porosity conditions, they provided better attenuation of low-frequency noise. (4) At low porosity, the noise reduction effect of green spaces was primarily influenced by hedge width, and the DBH and height of trees and shrubs. During the dynamic process of leaf shedding, the key factors affecting noise reduction were the DBH and height of trees and shrubs.

Conclusion Noise reduction by street green space plants showed significant spatiotemporal heterogeneity, and the influence of optical porosity on noise reduction effect varied significantly among different types of green spaces. This study enriches the theoretical foundation of noise reduction by street greening and provides a scientific basis for control-oriented urban landscape design.