Take Care when digging near Blue Gum trees

This paper relates to the earlier post about recent telecoms work in Cardinal Avenue.

AS4970 The Protection of Trees on Development Sites defines the relevant rules, and applies to all interested in integration between trees and construction This Standard was prepared by the Standards Australia Committee EV-018, Arboriculture.  This Standard provides guidance for arborists, architects, builders, engineers, land managcrs, landscapc architects and contractors, planners, building surveyors, those concerned with the care and protection of trees, and all others interested in integration between trees and construction. The installation of in ground cabling is considered a form of construction.

Blue gum trees belong to a Critical Endangered Ecological Community, and are protected by a Threatened Conservation Species Act. Legal controls and Liabilities under common law need to be considered before disturbing the ground around these species.

Sydney Blue gums have a broad shallow root system with the majority of their feeding and anchoring roots confined to a depth of 30 - 60 cm below the surrounding soil.

The trenching that took place, most likely to a depth of 45 - 60cm as this is the required depth to place communication services in the ground, would have severed about 40% of the trees roots.

The cutting of roots close to the trunk within the structural root zone affects the tree’s stability and cutting roots further to the drip line of the foliage, known as the tree protection zone, severs the important feeding and anchoring roots.

The Structural Root Zone (SRZ) is an area around the base of a tree required for the tree’s stability in the ground that is necessary to hold the tree upright. The SRZ is nominally circular with the trunk at its centre.

The Tree Protection Zone (generally close to the edge of the outer foliage drip line) refers to an area around a tree to provide a specified area above and below the ground for the protection of a tree’s roots and crown to provide for the viability and stability of a tree to be retained where it is potentially subject to damage by trenching and excavation.

The main functions of roots include the uptake of water and nutrients, anchorage, storage of sugar reserves and the production of some plant hormones required by the shoots. In order for roots to function, they must be supplied with oxygen from the soil. The root system of trees consists of several 'types' of roots found in different parts of the soil and is generally much more extensive than commonly thought. The importance of roots is easily overlooked because they are not visible, that is 'out of sight, out of mind'.

 Damage to the root system is a common cause of tree decline and death and is the most common form of damage associated with trenching and excavation. In addition to lateral root spread being underestimated, root depth in trees has also been grossly exaggerated. Deep root systems or taproots are the exception rather than the rule. Most roots of most trees are found in the very top of the soil. The vast majority of these roots are small non-woody absorbing roots which grow upward into the very surface layers of the soil and leaf litter. This delicate, non-woody system, because of its proximity to the surface, is very vulnerable to injury.