The Effect of Pure and Mixed Plantations of Robinia Pseudoacasia and Pinus Eldarica on Traffic Noise Decrease

This research was conducted to determine the effect of three different plantation types including pure and mixed plantations of Robiniapseudoacasia and Pinuseldarica on noise pollution reduction in Chitgar forest park of Tehran. A point source of noise was positioned in front of each plantation type and the noise level at different distances was measured with a noise meter. Noise values were taken at four measurement points; open area as control treatment (without trees), the urban forests of pure stands of Pinus eldarica and Robiniapseudoacasia and mixed stand and at 7 various distances (10, 20, 30, 40, 50, 75,100m from the noise source, behind tree stands) and 5 repetitions. Among the measured points, mixed stands had the best effect on noise pollution reduction which was about 16.91 dB (A) (decibel) in the distance of 100 meters and up to the permitted level. Noise level reduction was 15.77 dB (A) 50 meter away from noise source within the same stand. Regarding to the negligible difference between the noise reduction effectiveness of these two distances and some limitations to develop urban forests, the tree belts with 50 meters width is recommended to reduce the noise pollution to its standard size.