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Trees and noise control

Noise is a common problem in both urban and rural areas, traffic noise in particular. Where space permits, trees and shrubs can make effective noise barriers and at the same time be visually attractive.

The results of research on the effectiveness of tree and shrub barriers vary enormously but in some cases, noise can be reduced by six decibels (dB) over a distance of 30 metres where planting is particularly dense. A belt of trees and shrubs between 15 and 30 metres wide can reduce the sound level by as much as 10dB.

There are several factors to be considered before deciding to create a tree or shrub barrier against noise. Where possible, use trees that will develop dense foliage and relatively uniform vertical foliage distribution or combinations of shrubs and taller trees to give this effect. Where the opportunity to use trees is restricted, use combinations of shrubs and tall grass or similar soft ground cover, in preference to paved, tarmac or gravel surfaces, to absorb noise rather than reflect it.

Some other points to bear in mind are:

  • noise is more effectively reduced by completely screening the source from view - gaps in a barrier still allow noise to penetrate
  • a noise barrier should be planted as close to the noise source as possible
  • widely spaced trees do not reduce noise effectively - wide belts and high densities are needed for significant noise reduction
  • effectiveness is closely related to the density of stems, branches and leaves - use trees with dense foliage and branches that reach close to the ground, plant an under-storey of dense shrubs or a surrounding hedge
  • for year-round noise screening, use broad-leaved evergreens or a combination of conifers and broad-leaved evergreens
  • soft ground is an efficient noise absorber. Avoid hard surfaces – asphalt and concrete reflect virtually all sound falling on them at any angle. Cultivating ground before planting and the addition of well-rotted organic matter to the soil surface, may also help to reduce noise while vegetation becomes established.