Noise pollution is the second biggest threat to human health and life after smog. We are increasingly recognizing this problem, although it is still downplayed. Occupational hazards aside, almost all people living in cities or near busy roads are exposed to noise.

Although we may not be fully aware of it, daily contact with noise is a significant stress on the body, which can lead to an increase in blood pressure and consequent cardiovascular disease. Nocturnal noise, in turn, can disrupt sleep, thereby reducing the quality of sleep and contributing to, among other things, difficulty concentrating and irritability, and ultimately causing hormonal and metabolic disorders in the long run.

In addition, while there is limited research on the effects of noise pollution on plants, there is sufficient evidence that noise has a cascading effect on entire plant and animal communities, which can have long-term or permanent consequences.

Do trees reduce noise?

Scientific studies show that trees can significantly reduce sound by absorbing, reflecting and refracting sound waves and “masking” noise with natural sounds.

Absorption

The study, published in Applied Acoustics, found that among 13 coniferous and deciduous tree species, larch bark absorbed sound waves best due to its rough texture. In addition, we found that coniferous trees absorbed more sound than deciduous trees.

Sound absorption efficiency was determined based on the structure of the tree, i.e. the height, shape and density of the leaves, branching structure, wood density and bark texture were important. Surprisingly, most of the sound was absorbed by the ground between the trees. Tree roots keep the soil loose, dead organic matter forms a spongy layer, while a canopy of leaves helps keep the soil moist, all of which makes the ground absorb sound much better.

Reflecting noise

Sound waves bounce best off hard surfaces, so hard, stiff tree trunks, especially those with dense bark like oak, for example, reflect sound best.

Breaking down

Sound waves are refracted as they pass through various mediums, such a medium could be tree crowns, for example, and the more texture in the leaves, branches, vines and bark, the better the effect.

Masking

The presence of trees can attract, for example, songbirds or crickets, which, producing sounds that are pleasant to the human ear, will mask the noise. You can also choose trees based on the sound they make, for example, species with thick leaves, such as quaking aspen or oaks that rustle even in a slight breeze. The rustling of leaves is a sound that has a relaxing effect.

How to design a sound barrier so that trees reduce noise?

When choosing plants as a sound barrier, it is important to suggest local conditions and ensure the best durability and effectiveness.

The width of the vegetation barrier and its distance from the noise source plays a key role in its noise-blocking effectiveness. The buffer placed closer to the noise source will block noise better, the differences in efficiency can be very significant. It is worth mentioning that 10 dB is perceived by humans as a reduction in noise by half, and proper space planning using greenery, can provide a reduction of 5 to 8 dB. (Acoustic screens in Poland reduce noise by a maximum of 10 to 12 dB, only if they meet all the conditions, usually these values are lower).

The best noise barriers have a diverse structure, so green screens should also include shrubs, herbaceous plants and climbers in addition to trees.

Do trees reduce noise better than artificial screens?

Can green barriers be better than concrete screens, concrete-steel screens, or transparent screens such as tempered glass, acrylic or polycarbonate panels?

Factors such as the aesthetics of the surroundings, environmental concerns (e.g., birds that die colliding with glass screens), costs, pollution absorption and health benefits for nearby residents would also need to be considered when making a final assessment.