Noise attenuation provided by hedges

During the past few decades, urban areas have experienced increasing environmental stress. Noise is considered as one of the most important sources of urban pollution with adverse effects on human health. Urban vegetation provides many ecosystem services including the reduction of noise pollution. Hedges are widespread in cities and have the peculiarity of being often grown close to the source of noise. The study investigated the noise reduction due to hedges of Prunus laurocerasus and Laurus nobilis and the effect of the vegetation on sound spectra. Four different trials were carried out, including the use of two different noise sources and the measurement of noise at different distances both from the green barrier and from the noise source. During one trial, the influence of the type of ground surfaces between the noise source and the receiver was also evaluated. In the three trials where a significant attenuation of the noise occurred, the porosity of hedges measured less than 4.6% and an average noise reduction of about 2.7 dB(A) (max 7.0 dB(A)) was observed. This effect was particularly relevant in the range of higher frequencies (between 2 and 20 kHz). This study can contribute to plan and design hedges in the urban context.