After a fiasco resulting from the planned removal of three trees on Rossi Street, Yass Valley Council has received a new report that goes against the previous findings.
The reassessment by a senior Level 8 Arborist has confirmed that two large London Plane trees and one White Cedar tree are all rated as low risk to public safety. This assessment remains valid for the next 12 months.
Council said they are now in discussion with Essential Energy to determine future management options for the trees, with the need to take into consideration their natural amenity while ensuring community safety and minimising potential disruption to power infrastructure.
Council said the options and assessments will also contribute to Council’s broader work on developing a comprehensive Tree Management Strategy for Yass Valley. Council thanked the community for its input to date and will keep residents informed as management strategies progress.
The safety barriers are now removed, and the saga seems to be over for now.
The report reads, “Tree 1 was identified as the exotic species London Plane (Platanus × acerifolia). At the time of inspection, the tree was dormant, but it appeared to be in fair to good health, with extension growth and canopy density typical of the species.
“London Plane is a large, fast-growing tree commonly used as a street tree in south-eastern Australia due to its tolerance of urban conditions and ability to withstand heavy pruning. Tree 1 is a mature specimen and is of similar age to the larger London Plane trees located on Meehan Street, adjacent to the bank.
“Tree 1 exhibited poor structure and form. Its canopy extends into the front yard of 100 Rossi Street to the south and over Rossi Street to the north. The tree has been consistently pruned into an “open vase” form to maintain statutory clearance requirements beneath the overhead HV powerlines. While this pruning was unavoidable, it has created over-extended first-order branches and contributed to a poor structural form. However, branch unions were sound, regrowth at old pruning wounds was well attached, and branch taper was good. The large lateral branching had sufficient taper to support the overextension created by constant reduction pruning.
“Good wound occlusion was observed at old pruning wounds, indicating the tree had good vigour and is capable of compartmentalising wood decay fungi that reduce wood strength. Sounding the branches with a sounding mallet around old wounds demonstrated that wood decay was superficial and contained.
“White Cedar [Tree 2] is a small to medium-sized tree at maturity and possesses characteristics well-suited for use as a street tree under powerlines. Tree 2 was mature and appeared to be of a similar age to other large mature trees observed elsewhere within the township.
“Tree 2 exhibited fair to good structure and form. Its canopy extends into the carpark of 116 Rossi Street to the south and over Rossi Street to the north. To maintain statutory clearance from the overhead HV powerlines, the tree has been consistently pruned into an open vase style. Branch unions were sound and good wound occlusion was observed at old pruning wounds, indicating the tree had good vigour, and is capable of compartmentalising wood decay fungi that reduce wood strength.
“Unlike the London Plane trees nearby, White Cedar matures as a shorter, more compact tree. This characteristic has made it easier to manage its size under the wires, with less significant structural compromise compared to the larger, faster-growing London Plane trees.
“Tree 3 was identified as the exotic species London Plane (Platanus × acerifolia). At the time of inspection, the tree was dormant and had been recently lopped back to a 3 m high stump.
“A Level 2 Tree Risk Assessment was undertaken using the International Society of Arboriculture’s (ISA) Tree Risk Assessment Methodology. The assessment was conducted from ground level as a visual tree inspection. A sounding mallet was used on Tree 1 to assess wood strength at decay wounds observed on lateral branches. No diagnostic or invasive testing (i.e. Level 3 assessment) was carried out.
“The ISA method requires assessors to apply professional judgment, supported by species knowledge and training, to derive a qualitative risk rating.
“The assessment was applied to all parts of each tree. For analysis, the highest risk scenario identified for each tree was used to determine the final risk rating. Assessments were made on a 12-month time-frame, meaning the likelihood of failure was considered in terms of the probability of part of the tree failing within the next one-year period.
“The assessment found no visual indicators suggesting structural failure ‘probable’ or ‘possible’. Within the next 12 months, it is unlikely that a part of these trees will fail in a way that could cause significant – severe property damage or personal injury. Accordingly, the trees are considered to have a low-risk rating over this period.
“London Plan and White Cedar both have strong, malleable wood characteristics that rarely fail under loading unless significantly compromised by decay fungi or poor branch attachment. London Plane and White Cedar are not prone to ‘sudden branch drop’. A poorly understood phenomenon where branches fail unexpectantly, with no visual indicators.
“London Plane is generally tolerant of heavy pruning. As Tree 1 continues to grow, its canopy will extend further towards the dwelling at number 110, and the wires, necessitating regular clearance works.
“If the trees were permitted to grow within the 2 m clearance requirement, the risk rating would increase, as wind could blow the smaller branches into the wires, causing conductor clashing. Conductor clashing can cause power disruption, fire and damage to the electrical infrastructure.
“To remain compliant, the trees will require ongoing annual pruning. These future management costs must be balanced against the amenity value the trees provide to Council and the community. Two arboricultural reports prepared by Mr Michael Reeves were also reviewed. While these reports contained some useful background information, they demonstrate a lack of training in ISA Tree Risk Assessment methodology.”
The report pointed to the following reasons specifically for making the claim:
• Mr Reeves’ risk assessment allegedly misapplied the ISA risk matrix.
• He rated the likelihood of impact as “likely”, despite his own assessment indicating a probable chance of failure and a medium chance of impact according to the report.
• Under ISA methodology, the report claims it should instead have been rated “somewhat likely.”
• It was also said there was no time frame allocated to the assessment. All trees will eventually fail.
The ISA methodology requires a time-frame; between 1 and 5 years is allocated for each assessment.
“As a result, his reported risk outcome of high was overstated. The correct outcome, based on his own findings, should have been moderate.”
– Jack Murray
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