Last updated on June 12th, 2022 at 02:25 pm
At least that’s what many people say! Is it true? It all depends on the angle from which one approaches the question.
From the physical point of view
No, trees do not protect against noise at all! The trunks are too easily bypassed, and the leaves are not a barrier at all! Worse, in fact, trees tend to add noise to noise, due to the rustling of leaves, the whistling of the wind in the branches and the singing of birds that perch there.
So, let’s take the example of a busy road. If a sonometric measurement is made on the roadside before and after a row of trees is planted, not only will the noise level not have decreased, but it will have increased!
From a psycho-acoustic point of view:
Yes, a row of trees can be effective! First of all, it hides the source of noise from view and makes the landscape pleasant. And for the brain, that counts! The noise is still there, but visually associated with something nice, and is therefore perceived as less invasive (this being said, we are talking about a purely psychological phenomenon whose effects vary greatly from one person to another. It will not work as well for everyone!)
On the other hand, the rustling of leaves is interpreted by the brain as background noise… And as it is also a noise that can be assimilated to white noise (containing all the frequencies of the spectrum), any other noise of a lower or equal sound level will tend to drown in it and will therefore be considered by the brain as also being part of the background noise… And will therefore be easily ignored.
Birdsong, on the other hand, is perceived by most people as a natural, pleasant and non-invasive noise (even if not everyone is tolerant of it). It increases the background noise without causing any disturbance (except in special cases).
Moreover, the fact of increasing the level of background noise is not without effect on what emerges from it. Noise annoyance is, to some extent, caused more by the difference between a particular noise and the surrounding background noise level (this is called acoustic emergence), than by the level of the particular noise itself. Thus, if the background noise increases, the emergence decreases and thus becomes significantly less annoying.
This being said, we can see that the effectiveness of a hedge or a row of trees is above all psychological, and its effect cannot therefore be guaranteed on everyone… On the other hand, it can be associated with a very real physical protection! If we take the example of our busy road, and if we mask it with a large landscape mound (a sufficiently high mound of earth is one of the most effective protections available!) or with a vegetated anti-noise wall, we win on both counts!… As long as the mound or the wall is judiciously placed, correctly sized and well installed.
This being said, we can see that the effectiveness of a hedge or a row of trees is above all psychological, and its effect cannot therefore be guaranteed on everyone… On the other hand, it can be associated with a very real physical protection! If we take the example of our busy road, and if we mask it with a large landscape mound (a sufficiently high mound of earth is one of the most effective protections available!) or with a vegetated anti-noise wall, we win on both counts!… As long as the mound or the wall is judiciously placed, correctly sized and well installed.