Managing Hazards and Risk

Managing Risks

Trees provide numerous benefits to those living and working in the urban environment, which increase with tree size and age. However, older and larger trees are also more likely to drop branches or cause root conflicts on the sites they inhabit. In managing these trees, tree owners must recognise both tree benefits and risks.

Hazards from trees may occur due to strong winds or storm events. Otherwise, construction or development may negatively affect trees. Tree owners should recognise tree risk and management strategies to help ensure trees are able to provide their full complement of benefits.

Recognising Tree Risk

Trees provide significant benefits to our homes and cities, but when trees fall and injure people or damage property they are liabilities. Understanding and addressing the risks associated with trees makes your property safer and prolongs the life of the tree.

An arborist can help you manage the trees on your property and can provide treatments that may help reduce the risk associated with certain trees. An arborist familiar with tree risk assessment may suggest one or more of the following:

Remove the target. While a home or a nearby powerline cannot usually be moved it is possible to relocate picnic tables, landscape features, vehicles or other targets to prevent them from being hit by a falling tree.
Prune the tree. Remove the defective branches or parts of the tree. Because inappropriate pruning may weaken a tree pruning work is best done by a competent qualified arborist.
Cable and brace the tree. Provide physical support for weak branches and stems to increase their strength and stability. Such supports are not guarantees against failure.
Provide routine care. Depending on seasonal changes and their natural shape mature trees need routine care in the form of water, nutrients (in some cases), mulching and pruning.
Remove the tree. Some trees with unacceptable levels of risk are best removed. If possible, plant a new tree in an appropriate place as a replacement.

Safe Response to Tree-Related Storm Damage

Severe weather can have a lasting impact on your home and the trees in the surrounding landscape. Tearing winds and penetrating rains work together, softening soils and overturning trees. Lightning strikes generate intense heat that vaporises water within the tree, causing wood to split and bark to explode. During a storm the failure of part or all of one mature tree may cause significant damage to personal property or powerlines.

Tree owners can follow these steps to help ensure a safe and effective response to tree-related storm damage:

Assess the damage.
Take safety precautions.
Resist the urge to do it yourself - call a professional arborist.
Employ a competent qualified and insured arborist.

Avoiding Tree Damage During Construction

Homes are often constructed near existing trees to take advantage of their aesthetic and environmental value. Unfortunately, the processes involved with construction can be harmful to nearby trees. Proper planning and care are needed to preserve trees on building sites. An arborist can help you decide which trees can be saved. The arborist can also work with the builder to protect the trees throughout each phase of construction.

Planning

Your arborist and builder should work together early in the planning phase of construction. Sometimes small changes in the placement or design of your house or driveway can make a great difference as to whether an important and valuable tree will survive. If open trenching for the installation of underground utilities cannot be routed away from trees then consider less damaging thrusting or under-boring techniques.

Erect Barriers to Limit Access

The most effective way to prevent damage to trees during construction is erecting barriers to prevent physical damage to the tree and its roots. Set up sturdy fencing around each tree to be retained, as far outwards from the trunk as possible - or, as a minimum, approximately 0.3m distance for each 2.5cm of trunk diameter.

If possible, limit access to the construction site to only one entrance/exit. Additionally, instruct all contractors where they are permitted to drive and park their vehicles on-site, to help avoid or reduce soil compaction and root damage. Limit areas permitted for the storage of construction materials, equipment wash-downs and other construction activities.

Maintain Good Communication

Communicate your objectives clearly to your arborist, builder and all subcontractors. Visit the site at least once a day, if possible. Your vigilance will pay off as workers learn to take your wishes seriously. Take photos at every stage of construction.

Treatment of Trees Damaged by Construction

The processes involved in construction can be devastating to surrounding trees if no measures have been taken to protect them. Remedial treatments may save some construction-damaged trees, but immediate implementation is critical. If you have trees that have been affected by recent construction a professional arborist can assess tree viability and risk potential and recommend treatment options.

Learn more about the treatment of trees damaged during construction

Inspection and Assessment

Because construction damage can affect the structure and stability of a tree your arborist should check for potential risks. A risk inspection may involve a simple visual inspection or instruments may be used to check for the presence of decay. Identified risks can sometimes be reduced or eliminated by removing an unsafe limb, pruning to reduce weight or installing cables or braces to provide structural support.

Common damage caused during construction includes:

Physical injury to the trunk and crown.
Soil compaction in the rootzone.
Severed roots.
Smothered roots from addition of fill soil.
Increased wind and sunlight exposure.
Stress due to ground-level and drainage changes.

Treating Trunk and Crown Injuries

Pruning. Split, torn or broken branches should be removed. Remove dead or diseased limbs from the crown of the tree. Postpone other maintenance pruning, such as crown raising, for a few years. Do not thin or reduce tree canopies to compensate for root loss.
Cabling and Bracing. If branches or tree trunks need additional support a professional arborist may be able to install a flexible dynamic cable supporting system and/or bracing rods. If cables or braces are installed they must be inspected regularly. Not all weak branches or trunks are candidates for these measures.
Treating Damaged Bark and Trunk Wounds. Bark may be damaged along the trunk or on major limbs. If this happens remove the loose bark. Jagged edges can be cut away with a sharp knife. Take care not to cut into living tissues. Do not apply paints or sealants.
Irrigation and Drainage. One of the most important tree maintenance procedures following construction damage is to maintain an adequate, but not excessive, supply of water to the rootzone. Water trees as needed, especially during the dry summer months. A long, slow soak across the entire rootzone is the preferred method of watering. Avoid frequent, shallow watering or over-watering. Poor drainage must be corrected or trees will decline rapidly.
Mulching. Apply a 50-100mm thick layer of organic mulch (such as wood chips or shredded bark) over a tree’s root system, extending out to the canopy dripline if possible, for a simple and effective means of enhancing root growth. The mulch helps maintain moisture, reduce competition from weeds and grasses and moderate soil temperatures. Extend mulch as far out from the tree's trunk as practical for the landscape site.

Monitoring for Decline and Risk

Despite your best efforts you may lose some trees from construction damage. Symptoms of decline include distorted, discoloured, smaller and fewer leaves, dieback in the crown of the tree and premature autumn colour. Stressed trees are more prone to attack by diseases and pests, reducing their health and potential lifespan. Severe damage and decline may also lead to defects and decay. Consult an arborist for a professional assessment if you are concerned with your tree’s health or structural integrity.