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19_01_16_AIA_Alba_25 Kauri St_V1 · MCU18/0165
Attached to the e-mail Arboricultural Impact Assessment report V1 - MCU18/0165.
Consult Arborist Pty Ltd
ARBORICULTURAL
IMPACT
ASSESSMENT
Project Address: 25 Kauri Street
Cooroy, QLD, 4563
Real Property Description: Lot 27 C 56016
Commissioned by: Alba Projects Pty Ltd
On behalf of: Calezac Pty Ltd
Responsible Council: Noosa Council (NC)
Council Reference: MCU18/0165
Date: 16/01/2019
Prepared by:
Matthew Duncan
Director / Principal Arborist
AQF Level V, TRAQ, QMQAA
e: [email protected]
m: 0450 355 770
ABN: 68 153 548 531
TODAY’S TREES FOR TOMORROW
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Consult Arborist
This document was prepared for the sole use of Calezac Pty Ltd and any regulatory agencies
involved in this project. No other party should rely on this information without the prior written
consent of Consult Arborist and Calezac Pty Ltd.
The findings laid out in this report are valid for 12 months from the date of the assessment.
If the advice and recommendations made in this report are not strictly adhered to, no
responsibility will be taken for the continuing health and condition of retained trees. Trees are
dynamic living organisms that respond to changes in their environs; repeat assessments are
key to maintaining tree vitality, structural integrity and to reduce any potential risk they may
pose.
C OPYRIGHT
This report/document is subject to copyright laws and penalties @280c per word per incident,
no part may be reproduced or used without the written permission of Consult Arborist Pty Ltd.
No responsibility will be accepted by Consult Arborist Pty Ltd for unauthorised or partial use
of this report.
General Permission of use as subject to Consult Arborist Pty Ltd copyrights:
1. Customer permission:
No more than three hard copies to exist at any one time.
2. Customer email permissions:
Must be original PDF format and limited to agreed Parties with a direct and vested
interest in the case.
D OCUMENT C ONTROL
The latest approved version of this 19_01_16_AIA_Alba_25 Kauri St_V1 should be available
to all personnel involved in the project in consultation with Consult Arborist Pty Ltd.
Each new revision should be distributed to all key personnel for review and endorsement.
All individuals working near protected trees are to be made aware of this document and it is
the responsibility of the individual to implement and/or adhere to the recommendations and
guidelines.
Version Date Written Reviewed Approved
Draft 14/01/2019 MJD SCD MJD
V1 16/01/2019 MJD SCD MJD
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Consult Arborist
D OCUMENTS R EVI EWED
The following documents have been reviewed, analysed and referenced during the production
of this report.
Reference / Date Title / Details
17/12/2018 Site Plans - 25 KAURI ST ISSUE 16 17-12-2018 Amended
driveway marked
360 Civil Consulting - 181002_25 Kauri St_Cooroy_B_Final
01/11/2018 Noosa Council Information Request
Note: Extracts from the above document have been used to illustrate the text within this report but should be read with full
documents.
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Consult Arborist
T ABLE OF C ONTENTS
Copyright .............................................................................................................................. 2
Document Control ................................................................................................................. 2
Documents Reviewed ........................................................................................................... 3
Table of Contents.................................................................................................................. 4
1 Brief ............................................................................................................................... 5
2 Site Inspection ............................................................................................................... 5
3 Site Location and Details ............................................................................................... 6
3.1 Site Maps/Plans ...................................................................................................... 7
4 Scope and Limitations .................................................................................................... 8
5 Tree and Site Assessment ............................................................................................. 9
5.1 Tree 1 – Olivine Street Frontage ............................................................................. 9
5.2 Trees 2 & 3 - Olivine Street Frontage .................................................................... 11
6 Tree / Canopy management......................................................................................... 14
7 Additional Observations ............................................................................................... 15
7.1 Road Junction Upgrade ........................................................................................ 15
7.2 Stormwater and Sewer Upgrade ........................................................................... 16
8 References: ................................................................................................................. 17
9 Assumptions and Disclaimer ........................................................................................ 17
Appendix 1 - Definition of Terms ......................................................................................... 18
Appendix 2 – Tree Risk Assessment Methodology ............................................................. 19
Appendix 3 - Definition of ISA Terms .................................................................................. 19
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Consult Arborist 1 B RIEF This assessment was commissioned by Colin Brown, Alba Projects Pty Ltd on behalf of the Client Calezac Pty Ltd; Consult Arborist Pty Ltd has been requested to conduct an Arboricultural Impact Assessment on subject trees located on the Noosa Council road reserve fronting the site at 25 Kauri Street, and the junction with Olivine Street, Cooroy in response to an Information Request from Noosa Council dated 1st November 2018. The Information Request is seeking information relating to mature trees only, adjacent to the site frontages; see relevant IR section below. Landscaping Information Required 7. Provide amended plans showing the retention of mature trees along the Olivine and Kauri Street frontage with boundary fencing located to accommodate the mature trees. 8. Provide an assessment by a certified arborist using the ISA Tree Risk Assessment Framework regarding the works necessary to retain the mature native trees along the frontages during operational works and the use of the premises. 9. Provide amended plans showing the crossover on Olivine Street outside the tree protection zone of the mature gumtree 10. Provide a landscape concept plan which identifies the retention of the native mature trees in the road reserve, signature landscape trees, frontage treatments, provision of shade trees within the development area and overall soft landscaping provided within the site. 2 S ITE I NSPECTION Matthew Duncan, Director and Principal Arborist of Consult Arborist, undertook the Visual Tree Assessment of the site from a ground level on Thursday, 10 January 2019. Matthew holds an AQF Level 5 (AHC50510) Diploma in Arboriculture from Sunshine Coast TAFE, an International Society of Arboriculture’s Tree Risk Assessment Qualification 2015 and has worked in the arboricultural industry since 1994. Since its establishment in 2011, Consult Arborist has been engaged to provide arboricultural advice and guidance on private, civil and capital works projects from cross-sector clients throughout SEQ. 19_01_16_AIA_Alba_25 Kauri St_V1 Page 5 of 19
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Consult Arborist 3 S ITE L OC ATION AND D ETAI LS The property of 25 Kauri Street is a triangular plot located on the corner of Olivine Street within the Noosa Council suburb of Cooroy. Currently, the site is a vacant Lot approximately 4,700m² and is covered with natural grassland and a sporadic mix of native trees. The road reserves of Kauri and Olivine Streets both have a mix of naturally occurring and planted trees with the established street treescape on Olivine Street. The total site area is proposed to be developed with the construction of 17 Units and the requirement for all trees within the site boundary to be cleared. As part of the development, it is expected that service installation, road widening, and the construction of driveways and public pedestrian footpaths will impact on the roadside vegetation. This assessment is based on the current design and site layout, as referred to in Documents Reviewed, without alteration to the Project layout. This report relates primarily to three (3) mature eucalyptus trees on the Olivine Street frontage of the site for which Noosa Council has expressed that retention is the desired outcome. These subject trees are identified using site plans and pictures. Comment and guidance will be provided on the subject trees and their suitability for retention within the currently proposed project design, and where required, with justifications and observations offered relating to the degree of intrusion in the calculated Tree protection Zones (TPZ) as per AS4970-2009 Protection of trees on development sites. All young and early mature trees located on the fence line of the site are to be removed. Planted street trees on Kauri Street are to be protected where the design allows. It is recommended that the Swamp Bush Box, Lophostemon suaveolens, is considered as a suitable species for replacement street tree planting, at 10m spacings where possible, to create a new street treescape. 19_01_16_AIA_Alba_25 Kauri St_V1 Page 6 of 19
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Consult Arborist
3.1 SITE MAPS/PLANS
Figure 1: Google map overview with site marked as a guide
Figure 2: Project overview with the three (3) subject trees plotted with approximate TPZ’s indicated
in green.
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Consult Arborist 4 S COPE AND L IMI TATIO NS The purpose of this report is to provide advice and guidance on the subject trees specifically within the Noosa Council road reserve Consult Arborist has reviewed the supplied documentation relating to the site, the existing trees/vegetation and the site layout with consideration to the design, future use and buildability of the Project. This report aims to provide guidance and direction with the practical consideration of the suitable retention of individual trees. The subject trees, as detailed within the report have received an International Society of Arboriculture (ISA) Basic Level 2 assessment with consideration to the design and future use of the project. The identification numbers and tree data has been allocated to the subject trees by Consult Arborist within the report to assist with calculations and identification. See attached photographs, plan extracts and maps for identification purposes. This report does not take into consideration changes to the site design or activities of which Consult Arborist has not been requested to comment on or been advised of. This report does not take into consideration extreme weather events or future pest and disease outbreak which may affect the tree’s health, condition and retainability. All assessments of the retained trees have been made visually from the ground and include the use of basic tools and techniques, i.e. cavity probing, minor root collar excavation, measuring tapes and devices and photography to gather information. No additional specialist equipment was used and no conclusive comments on what may have or may be happening within the internal structure of the tree will be made. No tissue or soil samples have been collected or submitted for testing. The information contained in this report is based on a visual inspection of the trees and their locations, species, health and condition at the time of the inspection from a ground level. The additional information provided is the author's opinion and is a 'snapshot in time' of the specific tree's health and condition at the time of the quoted inspection and no guarantee can be given that faults or issues may not arise in the future. The Tree Protection Plan advises on the methods for protection of the retained trees and is guided by the Australian Standard, AS4970-2009 Protection of trees on development sites, industry best practice and professional experience. 19_01_16_AIA_Alba_25 Kauri St_V1 Page 8 of 19
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Consult Arborist
5 T REE AND S I TE A SSESSM ENT
Three mature (3) trees have been individually assessed to provide information and clarity
regarding their suitability for retention within the project design, taking into consideration the
construction phase and future use of the site.
Noosa Council has expressed their desire that these three trees to be retained as part of this
development within the Council Road Reserve as Council Assets.
The allocated TPZ’s are estimated and provide a good representation of the calculated
protection areas required as per AS4570-2009 Protection of trees on development sites.
The results are to be presented to Noosa Council for consideration, and upon confirmation of
support should be incorporated into the final design and documentation.
5.1 TREE 1 – OLIVINE STREET FRONTAGE
DBH Height Spread TPZ SRZ
ID # Botanical name Common Name
(mm) (m) (m) (m) (m)
T1 Eucalyptus tereticornis Forest Red Gum 800 25-30 15-20 9.6m 3.2
*Measurements estimated by eye and experience.
The overall health and condition of the tree appear to be ‘Good' or typical for a mature tree of
this species; no major defects or disorders were noted at the time of the inspection.
The tree is located within the NC road reserve, 2.5 to 3m from the property boundary. On the
proposed design, two visitor car parking spaces in front of Unit 1 and a corner section of the
Community Garden are adjacent Tree 1 inside the site. In total this aspect of the design
intrudes by approximately 30% into the tree's calculated TPZ on the site side. This level of
intrusion is determined as Major and will require additional tree protection measures to be
implemented to reduce the impact on the tree’s health and ensure its suitability for retention.
In addition, due to the spreading form of its canopy, side branches on the development side
will intrude towards the corner of Unit 1. Selective pruning is necessary to reduce this intrusion
of branches that directly target the area of increased occupancy. It is also advised that
compensatory pruning is undertaken to balance the canopy as required; see Tree / Canopy
management.
Noosa Council has mandated the construction of a pedestrian footpath at 4m and a kerb at
8m. These works will result in up to 24% intrusion into the calculated TPZ and may also require
a rise in soil level over the entire road reserve (at this stage the depth required is unknown).
A shallow depth of topsoil will not cause the tree ill harm; however, the removal of the existing
ground vegetation will need to be considered and a method developed to minimise ground
disturbance. This level of intrusion is deemed as Major and will require detailed consideration
to ensure the impact is kept to a minimum and acceptable for the retention of the tree. It is
recommended that the footpath is constructed over the existing ground on a shallow depth of
fill to reduce excavation requirements.
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Consult Arborist
The realigned driveway is now located at a distance of 8m. This distance only represented a
minor TPZ intrusion and is not expected to cause major root loss. All earthworks and
construction within the tree's calculated TPZ is to be undertaken with care and under the
supervision of the Project Arborist.
Figure 3: Extract from site plans Picture 1: Tree 1
Due to Noosa Council's desire to retain this tree, a comprehensive Tree Protection Plan will
require implementation to minimise the impact of the project works on the tree. The protection
will be guided by, AS4790 – 2009 Protection of trees on development sites, industry best
practice and the supervising presence of a suitably qualified and experienced Arborist with a
high level of experience as an onsite Project Arborist.
The level of intrusion and likely root/ground disturbance that will occur is to be acknowledged
by Noosa Council along with the knowledge that although care will be taken to protect the
subject tree, decline in the tree’s long-term health/vigour may occur over the following years
on completion of the project.
Although not ideal, with acceptance by Noosa Council, the retention of Tree 1 is viable.
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Consult Arborist
5.2 TREES 2 & 3 - OLIVINE STREET FRONTAGE
DBH Height Spread TPZ SRZ
ID # Botanical name Common Name
(mm) (m) (m) (m) (m)
T2 Eucalyptus tereticornis Forest Red Gum 600 14-18 8-10 7.2 2.85
T3 Eucalyptus tereticornis Forest Red Gum 700 15-20 10-15 8.4 3
*Measurements estimated by eye and experience.
These two (2) trees are similar in location and form. Their overall health and condition appear
‘Good' or typical for a mature tree of this species with no major defects or disorders noted at
the time of the inspection.
The trees are located on the project boundary fence line with early mature naturally occurring
native and exotic trees species forming an understory. The project design positions these two
trees to the west of the Olivine Street driveway and directly to the rear of Units 11 – 17.
Noosa Council has expressed a need for the retention of these two trees to be reviewed as
they were originally proposed for removal.
Figure 4: Extract from the provided site plans with
tree locations marked and estimated TPZ shown in green
An upgrade of the road reserve has been mandated by Noosa Council with the proposed
construction of a pedestrian footpath and kerb positioned on the outer edge of the trees'
calculated TPZ which is not deemed as major TPZ intrusion.
The courtyard gardens of Units 11- 17 will be 6m deep from the property boundary beyond
which is the position of the dwellings (Units 11-17). On the plan, the intrusion into the trees'
TPZ is only classed as minor (up to 10% on one side). The primary cause for concern is the
construction/earthworks that will take place within the courtyard garden spaces including the
removal of the existing grass, any change in soil levels and the construction of fencing, paths,
hard landscaping, etc. These works will affect 50% of the trees' TPZs which is not considered
an acceptable amount of intrusion.
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Consult Arborist On completion of the development, the two subject trees will be positioned on the fence line directly to the rear of the complex residential dwellings, with branch encroachment over the courtyard gardens and with canopies within targeting distance of the dwellings. Accepting that these eucalyptus trees will drop debris, including leaf and twig, constantly, and with small branch failure common, these trees will cause a nuisance to the new occupiers that in turn, will place pressure on Noosa Council to resolve/manage. Their proximity to dwellings propounds an element of safety that needs to be considered. An ISA Tree Risk Assessment has been undertaken to determine the increase in risk that could ensue. For further explanations see Appendix 2 – Tree Risk Assessment Methodology and Appendix 3 - Definition of ISA Terms. Currently, the Occupancy beneath these trees is rated as Rare or Occasional with the likelihood of branch failure impacting a target as Very Low. When the development is completed, this will change to a 'Constant' occupancy rating with the target (dwelling/private property) having a 'High' likelihood of the target being impacted with minor to severe consequences depending on the size of the branch drop. The resulting Matrix 2 - Level of Risk is Moderate to High. This level of unprotected exposure from a forestry type eucalyptus trees is generally not recommended with the tree’s removal and replacement with a suitable urban treescape species a more viable long-term option. Picture 2: Tree 2 with dense understory Picture 3: Tree 3 While it is not recommended from an arboricultural risk perspective, if it is the desire of Noosa Council to retain these trees, a comprehensive Tree Protection Plan will require implementation to minimise the impact of the project works. The protection will be guided by, but will not adhere to, AS4790 – 2009 Protection of trees on development sites, nor industry best practice and the supervising presence of a suitably qualified and experienced Arborist with a high level of experience will be required as an onsite Project Arborist. 19_01_16_AIA_Alba_25 Kauri St_V1 Page 12 of 19
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Consult Arborist To ensure minimal disturbance to the TPZ, the garden areas will become access restricted during the building stage. This area will need to be fenced off to form a TPZ area and access only with permission from the Project Arborist. The level of intrusion and likely root/ground disturbance that will occur is to be acknowledged by Noosa Council along with the knowledge that although care will be taken to protect the subject tree, decline in the tree’s long-term health/vigour may occur over the following years on completion of the project. The close proximity of the trees to the dwellings will require the custodian's commitment to on-going monitoring routine with completion of recommended remedial works. Although not ideal nor recommended, with acceptance by Noosa Council of the level of intrusion and need for future ongoing maintenance, the retention of Trees 2 & 3 is viable. 19_01_16_AIA_Alba_25 Kauri St_V1 Page 13 of 19
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Consult Arborist
6 T REE / C ANOPY MAN AG EMENT
As part of the tree protection measures, it is recommended that each tree is pruned prior to
construction works as the first stage of the trees' ongoing maintenance and hazard mitigation
regime that will be continued by Noosa Council.
• Reduce side branches on the property side to suitable pruning points to reduce (not
remove) side lateral encroachment.
• Prune as required side lateral branches on the opposing side to help rebalance the
canopy form of each tree.
To ensure the pruning is correctly and safely completed the use of an Elevated Works Platform
(Cheery picker) is recommended.
Pruning works are to be undertaken in accordance with Australian Standards AS4373-2007
Pruning of amenity trees.
Pruning works are to be undertaken by a suitably qualified, trained and experienced AQF
Level 3 Arborist. The pruning is also to be overseen and guided by the suitably qualified,
trained and experienced Project Arborist AQF Level 5
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Consult Arborist
7 A DDI TION AL O BSERV ATIONS
As part of the required upgrades to the Noosa Council road reserve, roadway and the
installation of services the following additional street trees will require removal.
7.1 ROAD JUNCTION UPGRADE
One (1) early mature Hills Weeping Fig, Ficus microcarpa var. hillii, planted on the corner of
Kauri and Olivine Street requires removal due to the reconfiguration of the road junction. It is
also recommended that the six (6) young planted Weeping Figs, Ficus benjamina, are
removed as they are an unsuitable species for a road reserve treescape.
Figure 5: Extract of 360 Civil Consulting engineering plans
Kauri / Olivine Street junction
Picture 4: Hills Weeping Fig at the junction
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Consult Arborist
7.2 STORMWATER AND SEWER UPGRADE
An early mature Forest Red Gum, Eucalyptus tereticornis, and a Swamp Bush Box,
Lophostemon suaveolens, are located on the northern corner of the Kauri Street frontage
directly adjacent to the current stormwater catchment pit and headwall. As part of the
stormwater and sewer engineering upgrades to the infrastructure, earthworks are required in
the location of the trees resulting in direct conflict and the necessity for removal.
Figure 6: Extract of 360 Civil Consulting engineering plans .
Sewer and stormwater upgrade
Picture 5: Subject trees in conflict with Picture 6: Trees adjacent to the existing
infrastructure upgrade headwall
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Consult Arborist
8 R EFERENCES :
• Australian Standards ® AS 4970 – 2009 Protection of trees on Development Sites
• Australian Standards ® AS 4373 – 2007 Pruning of amenity trees AS 4373—2007.
• ISA Tree Risk Assessment
• ACA, STARS
• Evaluating Tree Defects – A Field Guide by Ed Hayes, Second Edition
• Body Language of Trees - Research for Amenity Trees, Claus Mattheck
• Smiley E. Thomas, Nelda Matheny and Sharon Lilly April 2012. Tree Risk Assessment: Levels of Assessment
9 A SSUMPTIONS AN D D ISCL AIM ER
This information contained in this report has been prepared on an independent basis, free of any bias and
represents the honest opinion of the consulting arborist.
All data is based on visual inspection of the tree/s and its/their location at the time of writing, unless otherwise
stated, and contains opinions, advice and recommendations based on information and data gathered from site
inspections carried out by the author and information supplied by the Client (Calezac Pty Ltd).
All information received from the Client shall be deemed to be true, accurate and up to date.
To the extent permitted by law, you agree Consult Arborist Pty Ltd is not liable to you or any person or entity for
any loss of or damage caused or alleged to have been caused (including loss or damage resulting from negligence)
either directly or indirectly, by your use of the information made available in this report. In no event will the author
be liable to you for any lost revenue or profits, or for special, indirect, consequential or incidental damage (however
caused and regardless of the theory of liability) arising out of or related to your use of that information, even if the
author has been advised of the possibility of such a loss or damage.
Consult Arborist cannot be held responsible for the effects of non-conformance works performed, by unsuitably
qualified staff or without the supervision of Consult Arborist.
Unless otherwise stated this report cannot be used within a court of law or any legal situation without the prior
consent of Consult Arborist Pty Ltd. The author shall not be required to give testimony or to attend court by reason
of this report unless subsequent contractual arrangements have been made.
The information contained in this report refers only to the tree/s that were inspected on 10/01/2019 and reflects the
condition of the tree/s at the time of the inspection.
There is no warranty or guarantee, expressed or implied, that the problems or deficiencies of the plants or property
in question may not arise in the future. Likewise, remedial treatments cannot be guaranteed.
Arboriculturalists cannot detect every condition that could possibly lead to the structural failure of a tree. Trees are
living organisms that fail in ways we do not fully understand. Conditions are often hidden within trees and below
ground. Consult Arborist Pty Ltd and the author cannot guarantee that a tree will be healthy or safe under all
circumstances, or for a specified period of time.
This report does not take into consideration the possibility of extreme weather or other events over which Consult
Arborist Pty Ltd has no control.
Treatment, pruning and removal of trees may involve considerations beyond the scope of the Arboriculturalists
services, such as property boundaries and ownership, disputes between neighbours, sight lines, landlord-tenant
matters and related. Consult Arborist Pty Ltd cannot take such issues into account unless the complete and
accurate information is given to them. Likewise, Consult Arborist Pty Ltd cannot accept any responsibility for the
authorization or non-authorization of any recommended treatment or remedial measure.
Arboriculturalists are tree specialists who use their education, knowledge, training and experience to examine trees,
recommend measures to enhance the beauty and health of trees and attempt to reduce the risk of living near trees.
Trees can be managed, but they cannot be controlled. To live or work near a tree involves some degree of risk.
The only way to eliminate all risks associated with a tree is to eliminate the tree.
Clients may choose to accept or disregard the recommendations of Consult Arborist Pty Ltd or to seek additional
advice.
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Consult Arborist
A PPENDIX 1 - D EFINITION OF T ERMS
The following criteria have been used in the VTA and arboricultural appraisal to gather information and determine the required
management options on the grounds of public health and safety. Measurements are approximate, made visually by eye unless
otherwise stated.
Age Class:
Young: Early stage of growth, immature size
Early Mature: Fast growing well-established tree which has not yet reached mature size
Mature: The tree reached its mature size, exhibits slowing growth rates with early stages of naturally forming dead
or dysfunctional wood.
Over Mature: The tree has reached mature size and is unlike to increase significantly in height or mass. Retrenchment of
the upper crown with increased vegetative vitality in lower crown, increased fungal activity and wood decay,
increase colonisation by flora and fauna.
Veteran: Tree with advanced retrenchment, a reduced crown size and annual increment growth, extensive hollowing,
crown collapse, low vigour, advance heartwood decay, advanced colonisation by fauna and flora.
Health:
Good: Tree with no defects or disorders which are notable. Full canopy with good colour foliage. Minimal pathogen
damage.
Fair: Tree with minor defects or disorders which are notable. Some deadwood within what can be an unbalanced
canopy, foliage generally with good colour although some discolouration may be present typical of species
in location. Minor pathogen damage.
Poor: Tree with major defects or disorders which are notable. The tree has considerable deadwood present,
discoloured or distorted leaves indicating a further decline of the tree. Detrimental pathogen damage.
Dead: Dead or dysfunctional moribund tree.
Structure:
Good: Tree with good unions and no branch defects. Sound trunk with no / minor defects. Good buttress and root
structure.
Fair: Tree with minor defects or disorders which are notable. Small areas of bark missing. Small cavities or minor
unfavourable branch unions may be present. Minor damage to roots.
Poor: Tree with major defects, large hollows, weak unions and/or problematic damaged roots.
Hazardous: This implies a tree with a major defect that may fail at any time
Protection of Trees:
DBH: Diameter at Breast Height - The approximate diameter of the trunk is measured visually in millimetres at a
height of 1.4m.
TPZ: As specified in the AS 4970-2009 Protection of trees on development sites, the Tree Protection Zone (TPZ)
is the principal means of protecting trees on development site. The TPZ is a combination of the root and
crown area requiring protection. This area should be isolated from construction disturbance so that the tree
can remain in a viable condition. The TPZ incorporates the Structural Root Zone (SRZ).
The radius of the TPZ is calculated for each tree by multiplying its trunk diameter at 1.4m above ground by
12, e.g. 300mm [email protected] x 12 = 3.6m Tree Protection Zone (TPZ)
A TPZ should not be less than 2m or greater than 15m (unless crown protection is required).
SRZ: Structural Root Zone (SRZ), as specified in AS 4970-2009 Protection of trees on development sites, is the
surface area of protection required to maintain a tree’s stability – a larger area is required to maintain a tree
in viable health. It is only necessary to calculate the SRZ when major encroachment into a TPZ is proposed.
The SRZ for trees with a trunk diameter less than 150mm will be 1.5m.
Tree Retention Value:
This retention value comes from the Institute of Australian Consulting Arborists (IACA), 2010, IACA Significance of a Tree,
Assessment Rating System (STARS), Institute of Australian Consulting Arboriculturists, Australia, www.iaca.org.au -
http://www.iaca.org.au/home/index.php/publications/71-stars
The process uses the Retention Value – Priority Matrix by assessing the Tree Significance Assessment Criteria and crossing
it with the Estimated Life Expectancy to determine the following ratings:
High: Priority for Retention
These trees are considered important for retention and should be retained and protected. Design
modification or relocation of building/s should be considered to accommodate the setbacks as prescribed by
the Australian Standard AS4970 Protection of trees on development sites. Tree sensitive construction
measures must be implemented e.g. pier and beam etc. if works are to proceed within the Tree Protection
Zone.
Medium: Consider for Retention
These trees may be retained and protected. These are considered less critical; however, their retention
should remain a priority with removal considered only if adversely affecting the proposed building/works and
all other alternatives have been considered and exhausted.
Low: Consider for Removal
These trees are not considered important for retention, nor require special works or design modification to
be implemented for their retention.
Remove: Priority for Removal
These trees are considered hazardous, or in irreversible decline, or weeds and should be removed
irrespective of development.
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Consult Arborist
A PPENDIX 2 – T REE R I SK A SSESSM ENT M ETHODOLOGY
The methodology of rating risk used in this report is based on the following International Society of Arboriculture’s Tree Risk Assessment and is calculated
through the use of qualitative risk matrix tables.
Initially, the Likelihood Matrix is used to estimate how likely a failure will be to impact a target. This is calculated by categorising how likely failure is to occur
and combining that with how likely that failure is to impact a target, as per Table 1.
Matrix 1 – Likelihood Matrix
Likelihood of Impacting Target
Likelihood of Failure
Very low Low Medium High
Imminent Unlikely Somewhat Likely Likely Very likely
Probable Unlikely Unlikely Somewhat Likely Likely
Possible Unlikely Unlikely Unlikely Somewhat Likely
Improbable Unlikely Unlikely Unlikely Unlikely
Table 1: Matrix 1 – Level likelihood of impact to a target.
Once the Likelihood of Failure & Impact level is determined a final level of Risk Rating can be calculated by combining the Likelihood with the Consequences
of Failure for each identified risk. This ascertains an overall Risk Rating for the tree, determined in Table 2.
Matrix 2 – Risk Rating Matrix
Likelihood of Failure & Consequences of Failure
Impact Negligible Minor Significant Severe
Very Likely Low Moderate High Extreme
Likely Low Moderate High High
Somewhat Likely Low Low Moderate Moderate
Unlikely Low Low Low Low
Table 2: Matrix 2 – Level of Risk
Where multiple risks are noted these tables will be used for each risk and the highest level will be taken as the overall risk rating for the tree. In this scenario,
multiple mitigation options may be offered to the tree manager to return the risk to an acceptable level within a reasonable timeframe as guided in the Risk
Rating.
A PPENDIX 3 - D EFINITION OF ISA T ERMS
Likelihood of Failure
Improbable: The tree or branch is not likely to fail during normal weather conditions and may not fail in many severe weather conditions within the specified
time frame.
Possible: Failure could occur, but it is unlikely during normal weather conditions within the specified time frame.
Probable: Failure may be expected under normal weather conditions within the specified time frame.
Imminent: Failure has started or is most likely to occur in the near future, even if there is no significant wind or increased load. This is an infrequent
occurrence for a risk assessor to encounter and may require immediate action to protect people from harm.
Likelihood of impacting a target
Very low: The likely hood of the failed tree or part impacting the specified target is remote. Occupancy rates are rare with no protection or occasional
with moderate protection.
Low: It is not likely that the failure will impact the target. The occupancy rates are frequent with partial protection or constant with significant
protection.
Medium: The failure is as likely as not to impact the target. The occupancy rates frequent with single side exposure or constant with partial protection.
High: The failure is most likely to impact the target. Occupation is constant with no protection.
Occupancy rates
Constant: 24 hours a day, 7 days a week.
Frequent: A large portion of the day/week.
Occasional: The zone is occupied by people or targets infrequently or irregularly.
Rare: Not commonly used.
Consequences of Failure
Negligible: Low-value property damage or disruption that can be replaced or repaired, no personal injury.
Minor: Low to moderate property damage, small disruptions to traffic or infrastructure, or very minor injury to persons.
Significant: Property damage of moderate to high value, considerable disruption, or personal injury.
Severe: Serious personal injury or death, damage to high-value property or disruption of important activities.
Levels of risk
Extreme: Failure is imminent with a high likelihood of impacting the target, and the consequences are severe.
High: Failure is very likely or likely with significant consequences, or failure is likely with severe consequences.
Moderate: Failure is very likely or likely with minor consequences, or failure is somewhat likely with significant or severe consequences.
Low: Failure is unlikely with negligible consequences or failure is somewhat likely with minor consequences.
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