[kach22i]

Trees, any trees, any amount of trees and type of trees will do nothing for sound decay.

What will affect sound levels (measured)?

1. Square of the distance the sounds fades away.

2. Sight lines (concrete wall close to source or even a tall earth berm).



What will affect perception of sound levels (subjective):

1. Tall trees which block the view and sent/clean or filter the air.

2. Tall fence which gives privacy (that loud sound is on the otherside of the fence, what do I care).


All that said, in my own mind I like to think trees can diffract some sound. All that really means in real life is that the direction of the sound source will play tricks on you, and not much else.