Does Vegetation Reduce Noise? The Truth About Trees and Noise Barriers

The simple answer

The simple answer is: not very much, unless you have a very large amount of it.

Trees, shrubs and landscaping can make an area feel quieter and more pleasant, but they generally provide very little measurable reduction in environmental noise levels.

A typical row of trees or a landscaped strip around a development may only reduce noise levels by around 1 to 3 dB, which is barely noticeable to most people.

For comparison:

• A 3 dB reduction is only just perceptible under ideal conditions.
• A 5 dB reduction is generally considered noticeable.
• A 10 dB reduction is perceived as approximately halving the loudness of a sound.

Most noise barriers used for road traffic or industrial noise are designed to achieve reductions of 5 to 15 dB or more.

Why don’t trees work very well?

Sound behaves differently to light.

You can often see through vegetation, and if you can see through it, sound can generally travel through it as well.

To significantly reduce noise, vegetation needs to be:

• Extremely dense
• Continuous without gaps
• Close to either the noise source or the receiver
• Very wide

In practice, meaningful reductions typically require vegetation belts that are 30 to 100 metres wide, and sometimes much wider depending on the frequencies involved.

For most developments in urban environments, this simply isn’t practical.

So why do trees seem to make places quieter?

Vegetation provides several important benefits:

• It blocks views of the noise source
• It changes people’s perception of the environment
• It introduces pleasant natural sounds such as wind and birds
• It reduces reflections from hard surfaces
• It improves visual amenity

In many cases, this improvement in amenity is just as important as the actual acoustic benefit.

When does vegetation help?

Vegetation can be useful where:

• It supplements a solid noise barrier
• Large buffer distances are available
• Visual screening is important
• Community acceptance is a project objective

The best results are usually achieved when vegetation is used alongside:

• Acoustic barriers
• Earth bunds
• Building design measures
• Equipment selection
• Operational controls

The EcoAcoustics Approach

At EcoAcoustics, we view vegetation as an important part of integrated acoustic design, but rarely as the primary noise control measure.

The most successful projects combine:

• Source control
• Distance
• Screening
• Building design
• Landscaping