Noise pollution is so deeply ingrained and omnipresent in our cities that we seem to barely notice it anymore. Yet it has a considerable impact on both our health — the WHO believes that prolonged exposure to high noise levels can raise blood pressure and cause heart attacks — and on wildlife.

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Plants are precious and natural allies in combating this phenomenon, which is linked above all to road traffic and industrial activity. Vegetation reduces noise pollution by attenuating sound and lowering its intensity. Leaves, branches, trunks and shrubs absorb and deflect sound energy, offering a little relief to our ears and nervous system. Not all trees, however, are equally effective at this task.

Nothing reduces noise like the larch

The best tree in this respect has turned out to be the larch, a tree native to central Europe and belonging to the conifer genus Larix. This is the finding of a study conducted by a group of researchers at University College London (UCL), published in the journal Applied Acoustics.

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The researchers subjected thirteen tree species with differing bark characteristics to laboratory sound absorption tests, and the larch proved to be the most effective tree when it comes to absorbing noise.

The secret of conifers

The British scientists analysed trunk samples from several tree species commonly found in cities, such as cherry trees, pines, beeches, willows, poplars and alders, selected on the basis of specific criteria, including bark thickness, tree age and trunk diameter.

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The researchers found that conifers, and in particular the larch, are able to absorb sound better than broadleaf trees. "The factors influencing noise reduction by tree bark are bark thickness, tree age and bark roughness," Jian Kang, co-author of the study, explained to the BBC.

Designing cities with awareness

Trees in cities, in addition to contributing to the indispensable reduction of pollutants, cooling us down and brightening our days with their beauty, are therefore necessary for combating the wearing effects of noise pollution. We know that some species are more efficient than others, and the research findings could therefore help urban planners to use trees with greater awareness during the urban design process.

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"Selecting species with slightly more sound-absorbing bark can effectively reduce noise pollution and mitigate the negative effects of traffic and noise generated by industrial activity," said Kang. "Given that conifer bark absorbs sound slightly better than that of broadleaf trees, conifers could be used more widely in the creation of urban green spaces."