An infiltration approach to reducing pavement damage by street trees.

Planting of street trees in cities and other high-density urban environments can provide significant social, economic and environmental benefits. However, street trees in pavements can often lead to shallow root growth resulting in damage to pavements, kerbs, roads and buried services. This study investigated whether pavement damage by tree roots could be reduced by planting trees in a permeable pavement system with an underlying layer of 20 mm diameter gravel to direct tree roots deeper into the pavement structure. A six-year duration field experiment was conducted to compare the growth of trees and their root systems in a conventional impermeable pavement with growth in a series of permeable pavements with different depths of underlying gravel basecourse. The results demonstrated that permeable pavements with underlying gravel layers encouraged tree roots to travel deeper into the underlying subgrade soil, thereby reducing costly pavement damage. This effect was more pronounced with deeper rather than shallower basecourse layers. While permeable pavements affected tree root growth, they had no significant influence on tree height after six years' growth.