Northern Beaches Arborist Case Studies

The situation

We were asked to assess a large Norfolk Island Pine (Araucaria heterophylla) in the front yard of a residential property in Narrabeen. It was in fair condition for its species and age, and the ground-level assessment found no significant structural defects. That mattered: removal was not being justified by simply calling the tree dangerous.

Putting a number on the risk

A Quantified Tree Risk Assessment (QTRA) estimates the chance of harm from a tree each year, based on how likely failure is and what could be struck, so risk can be compared with accepted thresholds rather than described as “looks dangerous”. Here it considered three credible failure scenarios and the people and property within the failure area: pedestrians, vehicles, the dwelling and the adjoining property. The highest individual risk came from minor branches or deadwood, within the Tolerable range (as low as reasonably practicable). Major-limb and whole-tree failure were both in the Broadly Acceptable range.

The real problem: the root zone

The front boundary fence was damaged and needed repair or replacement. The report assessed that carrying out those works while keeping the tree would involve substantial encroachment into the tree's protection zone, extending into its structural root zone, which could affect structural roots, stability and long-term viability.

What we recommended

Removal was recommended because of the combination of the tree's position in a restricted front yard, the limits it placed on using the property, the damaged fence, the substantial encroachment needed to repair it and the disturbance reaching the structural root zone. Replacement planting of a suitable species in an appropriate location was also recommended.

Why this case matters

The risk assessment did not find an unacceptable risk of failure. The removal recommendation arose from the combined site constraints and the assessed impact that the required boundary works would have on the tree's protection and structural root zones. Any removal remained subject to the applicable Northern Beaches Council pathway. This is not a case of a tree being removed because it was in the way, and Council states it will not approve removal for fences.

The tree

We were asked to assess a mature Grey Gum (Eucalyptus punctata) at a residential property in Church Point.

What the inspection found

Canopy vitality was generally acceptable, with some dieback and deadwood. The more significant concern was at the base: a substantial basal wound with associated decay, considered unlikely to occlude or compartmentalise in the foreseeable future, leaving an ongoing entry point for decay organisms. Because the defect sat in the lower trunk and root crown, an area under substantial mechanical loading, the report raised concerns about residual structural integrity and progressive deterioration.

What we recommended

The report concluded that the basal defect, the decay and the potential for further deterioration created an unacceptable level of structural risk, and recommended removal to eliminate the risk to people and property within the potential failure area. Any removal still has to follow the right Council pathway.

Why this case matters

A tree can look healthy and still contain an important structural defect. Tree health and structural integrity are not the same thing, which is why a professional assessment looks at more than whether a canopy is green.

The development

An Arboricultural Impact Assessment was prepared for a proposed residential development in Frenchs Forest. Nine trees were assessed for condition and retention value, protection zones and development impacts, and to establish which could be retained. A Tree Protection Plan was also required.

Nine trees, different impacts

The report did not give every tree the same recommendation. Eight trees were proposed for retention and one for removal. A Willow Myrtle with major encroachment into its protection zone, and associated root loss, was recommended for removal.

Designing the driveway around the trees

Two retained trees had moderate encroachment from the proposed driveway. Instead of recommending their removal, the report specified that the driveway be built at existing grade using a permeable paving system, to reduce excavation, limit root disturbance, maintain tree vitality and let air and water keep reaching the root zone.

Protection during construction

The report set construction controls rather than stopping at the DA assessment: protection fencing where viable, protection in line with AS 4970-2025, and Project Arborist hold points before, during and after construction, with supervision of manual excavation and root pruning inside the retained trees' protection zones.

Why this case matters

An assessment like this is not only a decision about which trees stay and which go. Good development arboriculture can find construction solutions that let development and trees coexist. Here, eight of the nine trees were proposed for retention, with construction adapted where needed.

The development

A proposed residential development in Davidson required assessment of ten trees. The Arboricultural Impact Assessment considered each tree's condition, retention value, protection zones and the encroachment the development would cause. The results varied widely.

Trees that could not stay

Three trees stood directly in the development footprint and were recommended for removal. Three more were affected by a proposed retaining wall, with calculated root-zone encroachments above 20%, and were also recommended for removal because of the major encroachment and associated root loss.

Trees that could stay

Two retained trees had encroachments above 10%. Rather than removing them, the report adapted the construction method: building on piers to bridge the existing roots, with pier holes dug by hand, without an auger, under AQF Level 5 arborist supervision, so significant roots met along the way could be retained and protected. Two further trees had encroachments below 10%, which the report assessed as unlikely to significantly affect their long-term health or vitality when protected.

The result

Four of the ten trees were proposed for retention, with a formal Tree Protection Plan and Project Arborist hold points covering installation of protection before construction, supervision of excavation and root pruning, and a final assessment after construction and landscaping.

Why this case matters

Tree constraints should be considered during design. Sometimes removal is unavoidable where a tree sits in the footprint or major root loss cannot reasonably be avoided. In other cases, changing the construction method can allow important trees and their roots to be retained.