Vegetation reduces noise pollution through a phenomenon called sound attenuation, which is the reduction of sound intensity. Normal attenuation of sound occurs as the energy of sound dissipates over long distances until not enough energy is left to vibrate air molecules. Vegetation hastens the normal attenuation mechanisms of absorption, deflection, refraction, and masking.
Leaves, twigs, and branches on trees, shrubs, and herbaceous growth absorb and deflect sound energy. Refraction of sound waves occurs when sound passes through vegetative barriers and bends around plant structures. Vegetation generates masking sounds, as leaves rustle, branches sway, and stems creak. Sounds of wildlife attracted to urban vegetation, such as birds and insects, also mask noise pollution.