Trees that are to be retained within areas where construction is taking place need to fenced in for protection purposes. These fenced in areas are Tree Protection Zones. (TPZs)
The TPZ should always be as large as possible, however with densification being the order of the day these areas are becoming smaller and smaller.
At times the available space is so small that it is better to recommend the removal of the tree and its replacement.
The size of tree needs to be considered in relation to the density of living spaces being built. There is no point in retaining trees that will later be felled by the residents because they are too imposing on the space.
Arborists should always bear in mind that architects are not taught about trees or their root systems, and are often completely unaware of how damaging construction impacts are. It is important to try and get involved on a site as early as possible, preferably during the design phase. Many designs have been extensively compromised in order to retain trees that are later felled because they have been so badly compromised by the insufficient preservation measures or over optimistic but insensitive design.
Engineers have often very creative methods to minimise damage to trees, but these measures are best planned at the earliest stages of development.
It is better to preserve and retain fewer trees properly than to try and retain too many by employing wishful thinking. Arborists have experience of the high mortality rate of trees on sites. We are often still engaged with developments long after completion, felling the trees that were diminished in health and stature in small increments throughout the process. It takes up to 10 years for a tree to completely respond to construction damage.
Once the TPZ is established it must be considered a no go zone for any construction activity, this includes earth level changes, trenching for services, and storage of materials.
The shape of the TPZ should be the greatest and most generous space that can be excluded from the site.
The TPZ should preferably be erected before any civils or plant hire contractors get to site.
At an early stage of the project, the arborist may need to trim the trees of dead, dangerous and
diseased wood, and possibly thin crowns to reduce uptake and transpiration of water.
At this stage it is also probably necessary to trim crowns where they may intersect with the proposed structures, clear them from roofs and lift them from roadways. The chip arising from this should be used as mulch within the TPZ.
The trees within the TPZ will frequently be extensively damaged by root disturbance outside the zone, this comprises severing by trenching, crushing and compaction by raising the grade, or by earth moving machinery, and also the complete completely removal of a potion of the system by earth level changes that involve cutting away of the original ground levels.
In addition to the erecting of the TPZ, watering may be required to compensate for root damage. This would be deep watering, weekly. Specific quantities can be determined based on species and extent of disturbance.
Sites should be inspected by the arborist every two months throughout the construction process. Trees that have been stressed by impacts can be susceptible to a variety of diseases that can be addressed and their impacts on tree health can be minimised through timely interventions.
During the landscaping phase the TPZ will need to be removed to allow the horticultural development of the area to take place. The arborist should be consulted at this stage and given access to the landscape plan to determine the extent of potentially harmful impacts like fertilizer, irrigation trenches, hard landscaping and other interventions.