No. 204: The acoustic properties of trees and bushes The sound-absorbing effect of trees and shrubs is scientifically proven and easy to explain in physical terms: With their branches and leaves, plants present a physical obstacle to sound waves. Although the sound can penetrate them, it loses strength and is also partially reflected back. However, the noise reduction of individual plants and narrow, single or double rows of trees is very low due to their low mass. To achieve an effect comparable to that of a two metre high noise barrier, a 25 to 30 metre wide strip of woodland with dense vegetation is required. In densely built-up city centres, trees are therefore only suitable to a limited extent for noticeably reducing noise levels. The situation is different on the outskirts of cities: Here, green tree strips are a very effective measure for creating an acoustic barrier between housing estates and noisy roads, railway tracks and industrial and commercial areas. Source: Two hundred and fifty things architects should know, Michael Sorkin