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RFI - Attachment 3 - Arborcultural Impact Assessment Report · 132003.221108.3
“Your Local Tree Specialist”
Arboricultural Impact Assessment
Site Location:
27 Bayview Road,
Noosa Heads, QLD 4567
Prepared for:
Noosa Shire Council
Commissioned by:
Rick Egan
Prepared by:
Sam Carr
Specialist Arbor Services Pty Ltd
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Table of Contents
1 Quality Control ............................................................................................................................ 1
2 Introduction .................................................................................................................................. 2
2.1 Brief ..................................................................................................................................... 2
2.2 Method ................................................................................................................................. 2
2.3 Scope and Limitations .......................................................................................................... 3
2.4 Documents reviewed ............................................................................................................ 3
3 Observations................................................................................................................................. 4
3.1 The Site ................................................................................................................................ 4
3.2 The Trees.............................................................................................................................. 5
3.2.1 Risk Assessment .......................................................................................................... 5
3.2.2 Impact Assessment ....................................................................................................... 6
3.3 Tree Protection Plan and Recommendations ....................................................................... 7
3.3.1 General Tree Protection Measures ............................................................................... 7
3.3.2 Considerations .............................................................................................................. 8
4 Discussion .................................................................................................................................... 9
5 Conclusion ................................................................................................................................... 9
6 References .................................................................................................................................. 10
7 Glossary ..................................................................................................................................... 11
8 QTRA Method ........................................................................................................................... 13
9 Appendices – Contractor Use .................................................................................................... 16
9.1 Appendix A – Site Map ..................................................................................................... 16
9.2 Appendix B – Tree Assessment Table ............................................................................... 17
9.3 Appendix C - Site Specific Tree Protection Table ............................................................. 18
9.4 Appendix D – Tree Protection Plan ................................................................................... 19
9.5 Appendix E -Tree Images .................................................................................................. 20
10 General Acknowledgments & Legislation. ............................................................................ 24
10.1.1 General Tree Protection Measures ............................................................................. 25
10.1.2 Considerations ............................................................................................................ 26
Tree Report: (AIA-27 Bayview NH-120226) Report Number: 001
Prepared by (Sam Carr – Specialist Arbor Services Pty Ltd) Page ii
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1 Quality Control
Version Date Details Author Signature
A 12-02-2026 Site Visit & Samuel Carr Dip Arb
Data collection Consulting Arborist
B 22-02-2026 Draft Report Samuel Carr Dip Arb
Consulting Arborist
C 25-02-2026 Quality Check Sarah Gibson
D 25-02-2026 Final Samuel Carr Dip Arb
Consulting Arborist
& Sarah Gibson
Authors Qualifications
Sam Carr holds a Diploma of Arboriculture (AQF Level 5 – AHC50520), a Foundation Degree in
Science in Arboriculture and Tree Management (Level 5), and a Level 3 BTEC National Award in
Forestry and Arboriculture and has over 15 years industry experience. Certified in VALID Tree
Risk–Benefit Assessor and an accredited QTRA Risk Assessor (ID: 8685)
Disclaimer
The findings and recommendations contained in this report are based on an independent and
honest opinion, free of any bias of the consulting arborist.
All recorded statements, findings and recommendations contained within this report associated
with tree conditions does not take into account the effects of extreme or adverse weather conditions,
changes in land use, unpredicted accidents or acts such as vandalism which occur after the date
and time of the survey. The assessment of tree condition given within this report corresponds
directly to the date and time of survey, trees are dynamic living organisms subjected to abiotic and
biotic factors and therefore cannot be assumed to remain unchanged.
Copyright
This report/document is subject to copyright laws and no part may be reproduced or used without
the written permission of Specialist Arbor Services Pty Ltd. No responsibility will be accepted by
Specialist Arbor Services Pty Ltd for unauthorised or partial use of this report.
General Permission of use as subject to Specialist Arbor Services Pty Ltd copyrights:
Customer permission:
• Appendices – ONLY Contractor Notes - to be issues to relevant contractors undertaking
relevant work recommendations.
• No more than three hard copies to exist at any one time.
• Customer email permissions
• Must be original PDF format and limited to agreed Parties with a direct and vested interest
in the case.
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2 Introduction
2.1 Brief
This report has been prepared by Specialist Arbor Services Pty Ltd (SAS) on behalf of Rick Egan
Builders to present the findings of an Arboricultural Impact Assessment (AIA) in relation to the
proposed development at 27 Bayview Road, Noosa Heads and provide a Tree Management Plan
(TMP) to navigate the likely impacts.
My role as a Consulting Arborist is to gather facts by observations to assist in determining the best
Arboricultural codes of practices are applied and so that it follows the AS4373-2007 Pruning of
amenity trees & AS4970-2025 Protection of trees on development sites.
The purpose of this report is to firstly survey the trees and assess the projects impacts upon trees
that are located within the project boundaries and secondly, to advise on ways to mitigate the
impacts through recognised tree care and tree protection methods.
Detail has been requested in relation to the following instructions:
• To assess the overall condition and retention value of the subject trees.
• To determine the Notional Root Zones (NRZ), Tree Protection Zones (TPZ) and Structural
Root Zones (SRZ) of the subject trees.
• To determine whether the subject trees are expected to remain viable following the proposed
development.
• To propose recommendations that are expected to ensure that the subject trees would remain
viable post construction.
2.2 Method
A ground based Visual Tree Assessment (VTA) considering Tree: identity, estimated age, tree
dimensions, tree health, structure, and notable features, will be carried out in accordance with
internationally recognised tree assessment practices including but not limited to:
• Field Guide for Visual Tree Assessment (Claus Mattheck & Helge Breloer (1994)
• Lonsdale, D. 1999. Principles of Tree Hazard Assessment and Management.
The Stationery Office. London, UK.
• Mattheck, C. Bethege, K. & Weber, K. 2015. The Body Language of Trees. Karlsruhe
Institute of Technology. Karlsruhe, GmbH.
• Australian Standard AS4970 – 2025 ‘Protection of Trees on Development Sites’
A calculation of the Notional Root Zone (NRZ) and Structural Root Zone (SRZ) is conducted to
assist in understanding the degree of encroachment from the proposed works. Mitigation measures
are then developed to assist in reducing unwanted impacts occurring to retained trees. The trees
retention value is then assessed based on the above information. This data can be found within the
Tree Assessment Table and Tree Management and Tree Protection Fencing Plan, in addition to this
this report.
When a tree is deemed to have an obvious tree risk feature, a detailed assessment is carried out from
the ground using the QTRA tree risk app. This method calculates the risk of harm (RoH)
quantitively by considering probability of failure and the consequence if the failure was to occur.
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Method used to gather data include:
• Camera - to record images of the site and trees identified within this assessment.
• Arborist Tape - to measure stem Diameter at Standard Height (1.4m) (DSH)
• Nylon mallet - to identify wood decay through sounding.
• Mobile device – to record GPS location and data required for assessment.
• Tree heights estimated.
• Canopy spread paced estimates
2.3 Scope and Limitations
At a basic level assessment, trees are inspected from easily accessible ground. Climbing plants and
dense vegetation will not be removed to get a closer look unless an obvious tree risk feature
presents itself and the benefit outweighs the loss of vegetation and potential habitat.
When a tree is deemed to have an obvious tree risk feature, a detailed assessment is carried out from
the ground using the QTRA tree risk app. This method calculates the risk of harm (RoH)
quantitively by considering probability of failure and the consequence if the failure was to occur.
If more detail is needed regarding the likelihood of failure of;
• A tree
• Tree parts
• Extent of decay or;
• A closer look at a feature inaccessible from the ground
Options will be provided within the “tree management recommendations” found within the report.
• No aerial inspection of the tree(s) will be undertaken - Unless otherwise stated within the
brief of the report or additional requests are made by the client.
• No tissue sampling was undertaken. Assessment of tissues (living or dead) was from a
ground based visual inspection only.
• No soil nutrient tests or geotechnical soil compaction tests were undertaken.
• No advanced wood decay / structural integrity testing (such as Resistograph or sonic
(ultrasound) tomography) was undertaken. Where required the author undertook a basic
audible wood resonance test using a sounding mallet to determine any levels of potential
decay or lack of structural integrity present.
• No topography information used.
• Access to neighbouring properties was not permitted, therefore assessment was limited to
only parts of the tree visible from within the subject sites and measurements estimated.
2.4 Documents reviewed
• Australian Standard AS4970 – 2025 ‘Protection of Trees on Development Sites’
• Australian Standard AS4373 – 2007 ‘Pruning of Amenity Trees’
• Proposed Alterations & Additions September 2025, A – 04/09/2025 Draft Review
Tree Report: (AIA-27 Bayview NH-120226) Report Number: (001)
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3 Observations
3.1 The Site
Source: Queensland Globe – Site indicated via blue arrow
Vegetation at 27 Bayview Road, Noosa Heads is regulated under Noosa Plan 2020, Local Law No.
3 (Community Health and Environmental Management), and relevant Queensland vegetation and
wildlife legislation. Although the site is a residential allotment, it sits within the ecological
catchment of Noosa National Park, meaning trees on the property contribute to local habitat
connectivity.
Noosa Council has confirmed that an arborist report is required to support the proposed
development, ensuring that any native vegetation is properly assessed and impact correctly
identified.
The proposed renovations at 27 Bayview Road include demolition and reconstruction of the
existing driveway with a new garage.
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3.2 The Trees
Tree Species Health Structure Age Useful Life
ID Expectancy
1 Ficus benjamina Fair Fair Semi- 20-40
Weeping Fig mature
2 Eucalyptus Good Fair Semi- 20-40
microcorys mature
Tallowwood
3 Ficus benjamina Good Fair Semi- 10-20
Weeping Fig mature
4 Elaeocarpus Fair Fair Semi- 10-20
obovatus mature
Hard Quandong
5 Buckinghamia Good Fair Semi- 20-40
celsissima mature
Ivory Curl Tree
6 Cupaniopsis Fair Fair to poor Semi- 1-5
anacardioides mature
Tuckeroo
Six trees were assessed due to being in proximity to the proposed development as indicated on the
Draft Proposals.
Trees situated adjacent to the road outside of the development footprint which were not collected,
however, should be afforded tree protection measures due to the expected movement of vehicles
and machinery. These impacts are expected to be negligible due to the existing use and constraints
of the area and temporary fencing is proposed in order to mitigate any accidental encroachment or
storage of materials within these areas.
3.2.1 Risk Assessment
Assessment of the risk presented by the trees was undertaken using the Quantified Tree Risk
Assessment (QTRA) system. The most likely failure is deadwood or small diameter green branches.
Based on a Target value of 4; a Size value of 4 and a Probability value of 5, a Risk of Harm (RoH)
of less than 1 in 1million is calculated, ie. the tree is a Broadly Acceptable risk.
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3.2.2 Impact Assessment
Tree Species DTW NRZ SRZ Impacts Retain/
ID (m) (m) (m) Remove
1 Ficus 4 7.32 2.71 Minor Retain
benjamina Existing infrastructure within 1
Weeping Fig meter of stem base.
Resilient species.
2 Eucalyptus <1 9 3.04 Minor Retain
microcorys Existing infrastructure within
Tallowwood 500mm of stem base.
Existing infrastructure proposed for
upgrade.
3 Ficus 4 9.36 2.98 Minor Retain
benjamina Existing infrastructure proposed for
Weeping Fig upgrade
Upgrade to become 2 meters closer.
Tree is situated approximately 1.5m
below existing driveway.
Resilient species
4 Elaeocarpus 5 6 2.47 Minor Retain
obovatus Parking vehicles on existing
Hard roadway.
Quandong Works proposed outside NRZ
5 Buckinghamia 2.28 1.79 Minor Retain
celsissima Parking vehicles on existing
Ivory Curl roadway.
Tree Works proposed outside NRZ
6 Cupaniopsis 6 3.6 2 Null Retain
anacardioides Works proposed outside NRZ
Tuckeroo
Trees 1, 2, and 3 are deemed to be most likely impacted the most by the proposals due to the works
proposed. However given the topography of the site and the existing hard standing, the expected
root development is highly unlikely to reflect the calculated NRZ prediction and root proliferation
towards the existing hard standing surface such as the driveway and the road is expected to be
minimal. Impacts towards the retained trees are therefore expected to be minor and given the correct
protection measures the trees are assumed to remain viable.
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3.3 Tree Protection Plan and Recommendations
Tree Species NRZ SRZ Protection Measures
ID (m) (m)
1 Ficus 7.32 2.71 Erect NRZ fencing to the existing hard standing
benjamina surfaces – excluding the tree from the work site.
Weeping Fig Project arborist super vision required for any
demolition/excavation works within NRZ.
Stem protection recommended.
2 Eucalyptus 9 3.04 Erect NRZ fencing to the existing hard standing
microcorys surfaces – excluding the tree from the work site.
Tallowwood Project arborist super vision required for any
demolition/excavation works within NRZ.
Stem protection recommended.
3 Ficus 9.36 2.98 Erect NRZ fencing to the existing hard standing
benjamina surfaces – excluding the tree from the work site.
Weeping Fig Project arborist super vision required for any
demolition/excavation works within NRZ.
4 Elaeocarpus 6 2.47 Erect NRZ fencing to the existing hard standing
obovatus surfaces – excluding the tree from the work site.
Hard
Quandong
5 Buckinghamia 2.28 1.79 Erect NRZ fencing to the existing hard standing
celsissima surfaces – excluding the tree from the work site.
Ivory Curl
Tree
6 Cupaniopsis 3.6 2 Erect NRZ fencing to the existing hard standing
anacardioides surfaces – excluding the tree from the work site.
Tuckeroo
Roadside trees situated to the east and west of the property and trees opposite the property should
be protected by temporary fencing. The fencing is to be installed to the edge of existing
tarmac/concrete to mitigate accidental vehicle encroachment and storage of materials.
3.3.1 General Tree Protection Measures
The following protection measures and low impact methodologies have been provided to ensure the
subject tree is not impacted during excavations.
Appoint a Project Arborist (PA)
The PA should hold an AQF5 in Arboriculture and have at least 5 years’ consultancy experience.
The role of the PA is to provide guidance and clarification on the tree protection methods outlined
in this report. Additionally, the PA is to be available to provide feedback and ongoing assessments
of the tree and its protection measures throughout and following the development of the site, when
necessary.
Tree Protection Zone (TPZ/NRZ) fencing
A temporary TPZ fence is to be installed to protect as much of the calculated TPZ as practical. The
TPZ fence should meet the following criteria:
- The fence should be installed as soon as practical.
- The fence can be comprised of safety mesh or similar.
- No materials should be stored within the fenced off area.
- The fence should not be removed until the development has concluded.
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- The fence should be clearly signed ‘Tree Protection Zone – No Access’.
Tree Root Pruning
Any root pruning required should be completed with a sharp hand tool. The cuts should be made at
a right angle to the root so as to reduce wound size. No wound dressing is needed. No roots larger
than 30mm in diameter should be cut without prior consent from the PA.
Working in the calculated TPZ/ NRZ of the subject trees
Non-Destructive Excavation (NDE) appears it will not be adequate to conduct the ground work
required to facilitate the proposals. The PA is to be present during the demolition/excavation work
to provide guidance on root management and root pruning, if necessary.
Project Arborist Certification
The PA is to assess the trees once the development has been completed. The purpose of this
assessment will be to ensure the tree has not been negatively impacted or damaged throughout the
development. Health remediation may be recommended at this point in time if the tree shows any
signs of decline or damage.
3.3.2 Considerations
Under AS4970-2025 the TPZ is described as:
The Tree Protection Zone (TPZ) is defined in Clause 1.3.19 of AS 4970:2025 as:
"specified zone above and below ground and at given offsets from the trunk set aside to protect a
tree’s roots and crown where these might be damaged by development."
• The NRZ is the starting point for determining the TPZ.
The TPZ should be determined using various considerations in relation to the tree and proposed
encroachments. Additionally:
The Structural Root Zone (SRZ) is described as:
The Structural Root Zone (SRZ) is defined in Clause 1.3.17 of AS 4970:2025 as:
“Theoretical area around the base of a tree required for the tree’s stability in the ground.”
The woody root growth and soil cohesion in this area are necessary to hold the tree upright. The
SRZ is nominally circular with the trunk at its centre and is expressed by its radius in metres. This
zone considers a tree's structural stability only, not the root zone required for a tree's vigour and
long-term viability, which will usually be a much larger area and is referred to as the ‘(NRZ/TPZ)’.
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4 Discussion
The proposed development at 27 Bayview Road, Noosa Heads involves renewal of the existing
crossover, associated demolition and construction works. Based on the current design, the location
of retained vegetation and the expectation that root development does not correlate to the calculated
NRZ due to existing constraints, the overall level of arboricultural impact is expected to be minor,
provided all recommended tree protection measures are implemented and the works proceed under
the supervision of the Project Arborist (PA).
The demolition and reconstruction of the crossover occur largely within the footprint of the existing
structure, meaning no new encroachments are anticipated for Trees 1 and 2. The only additional
encroachment relates to Tree 3, where a small portion of the proposed works extends marginally
closer to the tree. Tree 3 is positioned below the existing driveway level on a rocky embankment,
and the site’s topography strongly suggests that most of the structural root development is oriented
downslope, away from the proposed works. As such, any root material encountered is likely to be
limited in size and functional significance.
Should root pruning be required, it will be undertaken under PA supervision, ensuring cuts are
made to appropriate standards and that root loss is minimised. Given the resilient nature of the
species, the anticipated level of disturbance is unlikely to compromise tree stability or long-term
health. While post-works plant health remediation may be recommended depending on the extent
and condition of any roots exposed during construction, the need for such intervention is considered
unlikely based on current site conditions.
5 Conclusion
Overall, it is expected the proposed works can be completed with low arboricultural risk, and
retained trees are expected to remain viable provided the prescribed protection measures and
supervision requirements are followed.
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6 References
Common sense risk management of trees: Landowner summary of guidance on trees and public
safety in the UK for estates and Smallholdings (2012). Edinburgh: Forestry Commission.
Mattheck, C., Bethge, K. and Weber, K. (2015) The body language of trees: Encyclopedia of visual
tree assessment. Karlsruhe, Germany: Karlsruher Institute für Technologie--Campus North.
Claus Mattheck & Helge Breloer (1994) FIELD GUIDE FOR VISUAL TREE ASSESSMENT
(VTA), Arboricultural Journal,18:1, 1-23, DOI: 10.1080/03071375.1994.9746995
Duncan Slater (2018) Natural bracing in trees: management recommendations, Arboricultural
Journal, 40:2, 106-133, DOI: 10.1080/03071375.2017.1415560
Mattheck, C., Bethge, K. and Weber, K. (2015) The body language of trees: Encyclopedia of visual
tree assessment. Karlsruhe, Germany: Karlsruher Institute für Technologie--Campus North.
Protection of trees on development sites, AS 4970 (2025). Sydney, N.S.W.: Standards Australia.
Pruning of amenity trees, AS 4373 (2007). Sydney, N.S.W.: Standards Australia.
Schwarze, F.W., Lonsdale, D. and Fink, S. (1997) “An overview of wood degradation patterns and
their implications for tree hazard assessment,” Arboricultural Journal, 21(1), pp. 1–32. Available at:
https://doi.org/10.1080/03071375.1997.9747146.
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7 Glossary
Age Category : The age of the tree is represented as Juvenile, Semi-mature, Mature or
Senescent.
Juvenile: A young tree, given normal environmental conditions for that tree it will not
yet flower or fruit.
Semi-mature: Able to reproduce but not yet nearly the size of a mature specimen in that
location.
Mature: Has reached or nearly reached full size and spread for that species in the
given location.
Senescent: Old age: health and / or structure is being adversely impacted by the ageing
process.
AMENITY VALUE A judgement of amenity and utility the tree provides - primarily based on
the trees visual contribution to the neighbourhood. Other contributing
factors include species, size, age, health and ecological value. Amenity
value does not consider the degree of risk associated with a tree. Trees on
neighbouring properties should be protected (unless otherwise negotiated
with the owner) regardless of the amenity value
CANOPY SPREAD Overall size of the canopy as looking from a plan view. Recorded at the
widest point.
CO-DOMINANT Two stems of approximately the same thickness and height originating from
STEMS the same position in the tree.
COMMON NAME A non-scientific name commonly used for that tree.
CROWN WIDTH See ‘Canopy spread’
DBH The diameter of the trunk measured at or near 1.4m above ground level.
(Diameter at Breast Where there is more than 1 stem originating below 1.4m the measurement
Height) recorded is calculated as described in AS 4970-2009 for multi-stemmed
trees.
DEAD Cessation of all metabolic processes (or very soon to be)
DEFECT An imperfection, weakness, or lack of something necessary. In trees, defects
are injuries, growth patterns, decay, or other conditions that reduce the tree's
structural strength.
DTW The distance (in metres) from the proposed works to the centre of the trunk
(DISTANCE TO at the base of the tree.
WORKS)
FORM Reference to the symmetry of the crown as observed from all angles and in
accordance with the morphology of that species, and documented as Poor,
Fair or Good.
HEALTH A trees vigour as exhibited by the crown density, leaf colour, seasonal
extension growth, presence of stress indicators, ability to withstand diseases
and pests, and the degree of dieback. Where a deciduous tree is inspected
without foliage and health is undetermined ‘?’ will be recorded.
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Dead: Cessation or near cessation of all metabolic processes
Poor: Indicating symptoms of extreme stress such as minimal foliage, or
extensively damaged leaves from pests and/or diseases. Death probable if
tree deteriorates further.
Fair: Not nearly of ‘Good’ condition (see below)
Good: Usual for that species given normal environmental conditions – full canopy
with only minor deadwood, normal leaf size and extension growth, minor
pest or disease damage
Excellent: Better than usual for that species under normal conditions
HEIGHT The distance in metres from the ground to the highest point in the crown,
calculated in the vertical plane. This measurement unless otherwise
specified is estimated.
INCLUDED BARK A tight union within a tree that has included bark (bark pressing on bark),
UNION often in a ‘v’ formation.
LOPPING / TOPPING The removal of parts of a tree giving no consideration to the trees natural
defence systems.
PRUNING Systematic removal of branches from a plant whilst giving consideration to
the trees natural defence systems.
REFERENCE Unique identifier assigned to an individual report by the author
RETENTION VALUE Relates to a combination of factors including condition, location, amenity
and ULE
Nil: Tree would be expected to die or fail in the near future or is of very high risk
or a significant weed
Low: Easily replaced or may become problematic if retained given the location
and species
Moderate: An asset to the area, retention is desirable, of fair to good condition, not
easily replaced
High: Prominent or valued tree with high amenity and low risk.
(Trees on neighbouring properties are assigned a 'High' retention value and
should be protected regardless of amenity value)
RISK The combination of the likelihood of an event and the severity of the
potential consequences.
STRUCTURAL ROOT The area around the base of a tree required for the tree’s stability in the
ZONE (SRZ) ground. The woody root growth and soil cohesion in this area are necessary
to hold the tree upright. The SRZ is nominally circular with the trunk at its
centre and is expressed by its radius in metres. This zone considers a tree’s
structural stability only, this is different from the root zone required for a
tree’s vigour and long-term viability, which will usually be a much larger
area (see TPZ).
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STRUCTURE Reference to the structural integrity of the tree with consideration of the
crown, trunk and roots. Determined using the Visual Tree Assessment
(VTA) method (Matheck and Breloer 1994). The failure of small (<60mm
calliper) live or dead limbs is normal and not considered here.
Very poor: Clear indications that a significant failure is likely in the near future
Poor: Signs of structural weakness obvious and failure likely, one might expect a
significant failure event within the next 5 years, possibly tomorrow
Fair: Signs of weakness present though not obviously significant, likely to
become worse over time
Good: No obvious signs of structural weakness
TREE NUMBER Identifying number allocated to individual trees or groups of trees, used to
locate trees using site plans or tags on trees.
TREE PROTECTION An exclusion / protection area measured at ground level nominally circular
ZONE (TPZ) with the trunk at its centre, expressed by its radius in metres.
The TPZ allows for protection of canopy and roots; both the structural roots
that give the tree stability and the smaller absorption roots. The radius of the
TPZ is normally calculated for each tree by multiplying the DBH × 12. The
minimum distance will be 2m and maximum 15 as stipulated in the
Australian Standard 4970-2009 – Protection of trees on development sites.
REFERENCE Unique identifier assigned to an individual report by the Author
ULE Useful Life Expectancy is an estimation of how many years a tree can
reasonably be retained in the landscape provided growing conditions do not
significantly worsen and any recommended works are completed. It takes
into consideration factors such as risk, species, age, health and site
conditions.
8 QTRA Method
The Quantified Tree Risk Assessment (QTRA) system, developed by Mike Ellison at Cheshire
Woodlands, applies established and accepted risk management principles to tree safety
management. The system moves the management of tree safety away from labelling trees as either
‘safe’ or ‘unsafe’ and thereby away from requiring definitive judgements from either tree assessors
or tree managers. Instead, QTRA quantifies the risk of significant harm from tree failure in a way
that enables tree managers to balance safety with tree values and operate to predetermined limits of
tolerable or acceptable risk.
By quantifying the risk from tree failure as a probability, QTRA enables a tree owner or manager to
manage the risk in accordance with widely applied and internationally recognised levels of risk
tolerance. QTRA further provides a decision-making framework which considers the balance
between the benefits provided by trees, levels of risk they pose, and costs of risk management.
Using QTRA, the land-use (Target) upon which trees could fail is assessed first. By valuing the
Target first, the tree owner and the risk assessor are able to determine whether or not, and to what
degree of rigour, a survey or inspection of the trees is required. Where necessary, the tree is then
evaluated in terms of its size and probability of failure. Ranges of value for Target, Size, and
Probability of Failure are entered into a QTRA calculator which generates a traffic light colour-
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coded risk of harm. The tree owner can then compare the risk to advisory levels for risk tolerance.
By taking a QTRA approach, tree owners commonly find they spend substantially less resources on
assessing and managing tree risk than they did previously, whilst maximising the many benefits
their trees provide. Moreover, in the event of a 'tolerable' or 'acceptable' risk being realised, they
are in a position to demonstrate the risk has been managed reasonably and proportionately.
The Quantified Tree Risk Assessment (QTRA) system, as proposed by Ellison in 2004, provides a
structured approach to evaluating the risk associated with trees by combining principles of risk
management with tree safety. Here’s a breakdown of the concepts and methodologies mentioned:
Definitions and Key Concepts
• Risk: Defined as the combination of the likelihood of a specific event occurring and the
severity of its potential consequences.
• Hazard: A potential source of risk. Hazards are not risks themselves but can contribute to
risk if there is a target present.
• Target: The presence of people or property that could be affected by the hazard.
QTRA System Overview
The QTRA system evaluates risk by considering:
1. Target Presence: Identifying if people or property are at risk if a tree or tree parts were to
fail.
2. Impact Potential: Assessing the severity of the potential failure, which involves the size
and nature of the tree and its parts.
3. Probability of Failure: Estimating the likelihood of the tree or tree parts failing.
The system calculates a figure known as the Risk of Harm (RoH), which quantifies the probability
of death or injury resulting from tree failure. This figure is compared against a threshold to
determine if the risk is acceptable or unacceptable.
Thresholds and Comparisons
• Threshold Value: Studies, including those by the British Medical Association (BMA),
NASA, and others, use a threshold of 1 in 10,000 (0.0001 or 0.01%) to distinguish between
reasonable and unreasonable risk.
• Contextual Risks:
o Risk of death from a road accident in Australia: 1 in 15,000 (2009) to 1 in 19,000
(2013).
o Risk of death from falling down stairs: 1 in 310,000.
o Risk of death from falling out of bed: 1 in 1.1 million.
Public Perception and QTRA’s Role
• Public Perception: Trees may seem riskier due to their size and appearance, or because of
emotional and subjective views. This perception can be influenced by the tree’s age or
significance.
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• QTRA System: By providing a quantitative assessment, QTRA helps to remove emotional
bias and urban myths from the risk evaluation process. It enables a rational decision-making
process regarding tree safety and management.
In summary, the QTRA system allows for a structured and objective approach to assessing tree risk,
balancing the need for safety with the desire to retain valuable trees. This method helps manage
public concerns by providing clear, data-driven insights into tree risk.
Figure 1- QTRA Advisory Risk Thresholds (Ellison 2005)
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9 Appendices – Contractor Use
9.1 Appendix A – Site Map
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9.2 Appendix B – Tree Assessment Table
Canopy Spread E-W (m)
Canopy Spread N-S (m)
Arborist Comment
Retention Value
Retain/ Remove
DAB (mm)
Height (m)
DSH (mm)
Structure
NRZ (m)
SRZ (m)
Amenity
Tree ID
Species
Health
ULEL
Age
1 Ficus benjamina Fair Fair Semi- 14 20 20 610 620 20 Medium Council 7.32 2.71 Retain Situated upon a steep rocky slope. Co-
Weeping Fig mature - Owned dominant stem with included bark
40 Tree union noted.
DSH measured below union.
Existing road / curb within 0.3m of the
stem base.
2 Eucalyptus Good Fair Semi- 18 14 18 750 820 20 Medium Council 9 3.04 Retain Minor encroachment may occur during
microcorys mature - Owned excavation work.
Tallow 40 Tree
wood
3 Ficus benjamina Good Fair Semi- 15 24 18 780 780 10 Medium Council 9.36 2.98 Retain Tree is situated on a steep rocky slope.
Weeping Fig mature - Owned Multi leader form with included bark
20 Tree unions noted.
DSH measured below union.
4 Elaeocarpus Fair Fair Semi- 16 8 10 500 500 10 Medium Council 6 2.47 Retain DSH measured below union.
obovatus mature - Owned
Hard 20 Tree
Quandong
5 Buckinghamia Good Fair Semi- 10 5 5 190 230 20 Medium Council 2.28 1.79 Retain TPZ fencing to be installed along the
celsissima mature - Owned curb edging of the existing hard
Ivory Curl 40 Tree standing.
Tree
6 Cupaniopsis Fair Fair Semi- 10 6 6 300 300 1- Low Council 3.6 2 Retain Dsh measured below union.
anacardioides to mature 5 Owned
Tuckeroo poor Tree
*Tree Protection Zones (10.1) are identical to the Notional Root Zones (NRZ) unless states otherwise.
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9.3 Appendix C - Site Specific Tree Protection Table
When to Proposed task Trees Id Tree Protection Measure To be Certified
perform task
Prior to Install Tree Protection All trees Tree Protection Fencing is to exclude trees Project Arborist – level 5
works Fencing as per the Tree assessed from the project where possible. Either Consulting Arborist to
Management Plan. and road situated at the extent of existing supervise works and provide a
verge infrastructure or to calculated TPZ. Certification Report on
trees. completion of works
Stem protection 1, 2 Stem protection is to protect the tree from
accidental contact from machinery or
vehicular movement.
During Demolition and removal of 1, 2, 3 Supervision required to assist civil team to Project Arborist – level 5
construction existing infrastructure, cut / work safely through the root zone of trees. Consulting Arborist to
fill or excavation works for Tree root management may be required by supervise works and provide a
infrastructure reinstatement the Project Arborist. E.g. root pruning Certification Report on
required as part of the completion of works
project within the TPZ /
SRZ of trees to be retained.
Completion Conduct final Certification All trees Final Certification that Tree Protection Project Arborist – level 5
of works Assessment of retained assessed measures have been implemented through Consulting Arborist to provide
trees and road all stages of construction a Final Certification Report.
verge
trees.
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9.4 Appendix D – Tree Protection Plan
Red dashed line indicates Tree Protection fencing.
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9.5 Appendix E -Tree Images
Tree 1 – Weeping Fig Tree protection fencing Tree 2 – Tallow wood
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Tree 2 – Tallow wood Tree 3 – Weeping Fig Tree 3 – Weeping Fig
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Tree 4 – Hard Quondong TPZ Fencing Tree 5 Ivory Curl
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Tree 6 Tuckeroo TPZ Fencing
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10 General Acknowledgments & Legislation.
First Nations People & Custodians of the Land
The Aboriginal and Cultural Heritage Act 2003 should be considered if an activity is likely to impact on Cultural Heritage. A person who carries out
work has a duty of care to undertake reasonable and practical measures to ensure an activity to does not harm Cultural Heritage.
Wildlife Considerations
The DEHP (Department of Environment and Heritage Protection) should be consulted regarding regulations concerning tree removal. The Nature
Conservation Act 1992 provides statutory protection for most species of native animals and any tree work which affects them may constitute an
offence. A qualified Fauna Spotter-Catcher should be consulted prior to treeworks being carried out where wildlife may be active.
Protected Trees
Prior to carrying out any tree work, it is recommended to check with the local authority to ensure there is no protection order placed on the trees.
Should any tree deemed to be legallyprotected, it will be necessary to consult the local Council before removal can be carried out. Please see the
additional mapping for more information.
Habitat Trees
When undertaking remedial tree works on habitat trees, please be aware of the fauna and their habitat. Creation of future habitat whilst undertaking
remedial works is to be considered. When mitigating hazardous deadwood, hollow sections and large branches, minimal pruning or reduction of weight
is required rather than total removal. Hollow sections take many years to be created and are a highly valuable habitat. Coronet cuts should be facilitated
where appropriate to mimic natural branch failure on suitable trees in a natural setting.
Contractor Notes
Recommended arboriculture works are to be carried out by an arborist holding a minimum of a Level 3 AQF qualification in Arboriculture. It is
expected that the Arborist may encounter anomalies within the tree as they climb/work and as such may use their discretion to remove any further
branches or limbs which they may deem could pose an immediate risk. Additional removals outside the recommendations or defects noted whilst in the
tree are to be recorded and reported to the author.
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10.1.1 General Tree Protection Measures
The following protection measures and low impact methodologies have been provided to ensure the subject tree is not impacted during excavations.
Appoint a Project Arborist (PA)
The PA should hold an AQF5 in Arboriculture and have at least 5 years’ consultancy experience. The role of the PA is to provide guidance and
clarification on the tree protection methods outlined in this report. Additionally, the PA is to be available to provide feedback and ongoing assessments
of the tree and its protection measures throughout and following the development of the site, when necessary.
Tree Protection Zone (TPZ) fencing
A temporary TPZ fence is to be installed to protect as much of the calculated TPZ as practical. The TPZ fence should meet the following criteria:
- The fence should be installed as soon as practical.
- The fence can be comprised of safety mesh or similar.
- No materials should be stored within the fenced off area.
- The fence should not be removed until the development has concluded.
- The fence should be clearly signed ‘Tree Protection Zone – No Access’.
Tree Root Pruning
Any root pruning required should be completed with a sharp hand tool. The cuts should be made at a right angle to the root so as to reduce wound size.
No wound dressing is needed. No roots larger than 30mm in diameter should be cut without prior consent from the PA.
Working in the calculated TPZ of the subject trees
Non-Destructive Excavation (NDE) is required within the calculated TPZ of the subject tree. NDE is required within proximity of Tree 1 for the
installation of the neighbouring underground services. NDE is required to remove the soil and other material so as to expose any tree roots that may be
present in the proposed location. The materials are to be installed with the intent of retaining as many tree roots as practical. The PA is to be present
during the excavation to provide guidance on root management and root pruning, if necessary.
Project Arborist Certification
The PA is to assess the trees once the development has been completed. The purpose of this assessment will be to ensure the tree has not been
negatively impacted or damaged throughout the development. Health remediation may be recommended at this point in time if the tree shows any signs
of decline or damage.
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10.1.2 Considerations
Under AS4970-2025 the TPZ is described as:
The Tree Protection Zone (TPZ) is defined in Clause 1.3.19 of AS 4970:2025 as:
"specified zone above and below ground and at given offsets from the trunk set aside to protect a tree’s roots and crown where these might be damaged
by development."
• The NRZ is the starting point for determining the TPZ.
The TPZ should be determined using various considerations in relation to the tree and proposed encroachments. Additionally:
The Structural Root Zone (SRZ) is described as:
is defined in Clause 1.3.17 of AS 4970:2025 as:
“Theoretical area around the base of a tree required for the tree’s stability in the ground.”
The woody root growth and soil cohesion in this area are necessary to hold the tree upright. The SRZ is nominally circular with the trunk at its centre
and is expressed by its radius in metres. This zone considers a tree's structural stability only, not the root zone required for a tree's vigour and long-term
viability, which will usually be a much larger area ‘(TPZ)’.
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Used in these records
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