Protection of urban trees from trenching damage in compact city environments

Abstract

Trees in greenspaces are an indicator of a city’s livability and sustainability. Roadside trees furnish linear greenery that can permeate neighborhoods and serve landscape and amenity functions. They are subject to high-intensity stresses and often perform poorly. Trenching to reach or install utilities along pavements is a major cause of tree damage and subsequent decline. Erroneously, it has been believed that roots grow mainly downwards and hence trenching near a tree is relatively harmless to roots. Although modern research confirms the shallow but wide distribution of tree roots that can be seriously damaged by trenching, old trenching practice still persists in many cities. Installing cable television and optical-fiber networks, and the need to overhaul dilapidated utility lines in old cities, could bring massive damage to roadside trees and significantly degrade cityscape quality. Recent advances in trenchless technology could merge with the new understanding of root distribution to protect this valuable municipal asset. Utility pipes or cables could be inserted below or around the root envelope in a drilled or bored channel, while extant pipe channels could be used to rehabilitate an old line. The procedures and precautions for the application of trenchless methods on narrow pavements are proposed.