It is a common practice to plant trees and shrubs near the boundary

It is a common practice to plant trees and shrubs near the boundary walls of buildings. What purpose do they serve?

The practice of growing and maintaining trees and shrubs near the boundary wall of residential or official building is a common practice.
This is because it acts as a barrier for sound and check noise pollution. This green belt of trees and shrubs also acts as an effective measure to check primary air pollutants like dust, flyash, etc.