Barnes & Associates
Rivermead, Skelton Road, Langthorpe, North Yorkshire, YO51 9BZ
Tel: 01423 322 371 Mobile: 07831 530 563
T ree R isk Assessment
Site: Snape Lime Avenue, The Avenue, Snape
Client: Mrs E Kirby
Date: 25/05/2016
Reference: BA5446
BARNES & ASSOCIATES
Page 2 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
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SUMMARY OF TREE INFORMATION The purpose of this report - This is an arboricultural assessment outlining the
condition and risk of the significant trees located along The Avenue, Snape located
close to the highway and adjacent to publicly accessible areas.
Its purpose is to provide initial information on the possible risk offered by the trees,
their condition, safety and suggest either further assessment or works to improve
safety and extend their safe life in addition to commenting upon the level of
suppression that the mature avenue of limes is having on the semi-mature trees in
the outer avenue.
Report Contents - The principal issues have been the ‘level of suppression that the
mature avenue of limes is having on the semi-mature trees in the outer avenue’, to
quote the recent report of Whitehead Associates Ltd, so that a comparison of
opinions may be made. The report includes:
a tree assessment, detailing significant issues with suggested works.
a tree risk assessment, which is prepared in line with best practice.
a tree schedule & survey plan within the appendices, which details the
principle management issues and trees that pose an elevated risk to the
site users and neighbours.
Background Information - Subject to physical access being available, to assess all the
significant trees on site from ground level. Problematic trees were inspected and
their details are discussed in the schedule of information, which is included in –
appendix B.
Carry out an assessment of trees situated throughout the site and carry out an assessment & risk assessment.
Produce a tree survey plan and tree risk assessment schedule setting out my survey data.
Produce a report setting out my methods, observations and opinions, and if appropriate, provide options for the management of the recorded trees.
Brief site description. The site has a well-defined green space and appears to have
had the same layout for many years.
I was provided with the general limits of the tree survey in red on the image below, used courtesy of suppliers notated on the image. I have outlined the limits of the tree survey in red on the Google Earth image below, downloaded and used courtesy of ©Google and ©third-party suppliers notated on the image below.
Risk Assessment. I have undertaken a tree survey to identify the general nature of
the trees and their relationship with significant targets. The level of detail with
which the trees have been assessed is informed by their relationship with targets.
Based on this larger trees adjacent to higher value targets were more closely
assessed than smaller trees adjacent to a lower value target.
My assessment identified 2 trees, which offer a High Risk when viewed over the
next year and poses an elevated risk of harm to site users and or neighbours, as
detailed in Table 1 below.
BARNES & ASSOCIATES
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These trees require mitigation / management to control the risk and meet your
requirements. High Risk Trees are highlighted Orange within my Tree Schedule in
appendix B, with their positions shown on the site plan located in appendix C, these
trees are discussed within this report.
In addition, I have identified 26 trees, which offer a Moderate Risk when viewed
over the next year and pose an elevated risk of harm to site users.
Again, these trees require mitigation / management to control the risk and meet
your requirements. Moderate Risk Trees are highlighted Yellow within my Tree
Schedule in appendix B, their positions are shown on the site plan located in
appendix C, these trees are discussed within this report.
The remaining trees are assumed to offer a Broadly Acceptable Risk at which point
the risk is already ‘As Low as Reasonably Practicable’ (ALARP).
Overall, the risk offered by the majority of the trees are low for users of the highway
and within the boundaries of tolerability that might ordinarily be applied by a
reasonable and informed landowner.
A universal principle of risk management is that the benefits of risk reduction (in
terms of reduced harm) should be balanced with the cost of that risk reduction (in
terms not only of the financial cost of implementing risk control measures but also
the loss of benefits that are conferred by the hazardous agency). Overall, finding a
balance between risks and benefits, effective risk management should seek to ‘do
no harm’.
The trees on site are a significant asset and help to both provide screening for the
site within the broader landscape, but also set the tone for the area giving it its own
unique character. As with any asset, such as a building or facility, the trees require
a level of investment to enable suitable levels of monitoring and management
works to be undertaken, to ensure continuity. If you require any further information
regarding the findings of this report, the management of the trees or would like
further information upon the value of the trees in terms of carbon sequestration or
overall asset values please feel free to contact me.
The trees as with any population of trees will require ongoing management and
assessment to maintain an acceptable level of risk and to help improve the
population as a whole. Ideally, this should be undertaken periodically and for many
sites alternating assessment between periods when trees are in and out of leaf,
allows assessments to centre on health and vitality or tree form and structure.
Please feel free to call and discuss these options if required.
The Current Recommendation. The Whitehead Tree Survey is broadly compliant with current best practice and discusses the level of suppression between the inner and outer lines of trees culminating in a complex site diagram which is informative though may prove difficult to digest by the almost 10% colour blind members of the population. Within the information however, there are several aspects in relation to the collection and presentation of information within in the original Whitehead report’s. Principally, there does not appear to be a Risk Assessment to enable a balanced approach to the prioritisation of the suggested works. This is typically the starting point for any Tree Assessment and understanding the risk offered to a site will inform management decisions and forms the basis of national and international methods of assessment. Further investigation though not detailed explicitly appear to have adopted invasive methods such as resistance drilling. Drilling devices will breach internal tree
Table 1 – Trees offering a High Risk of Harm
Tree No. Name
103 Lime
127 Lime
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defences and allow decay to spread and should therefore be kept to a minimum. Unfortunately, this does appear to have been undertaken needlessly on larger trees which have begun to develop adaptive tissue.
Some of the terminology within the report is a little unusual with repeated reference to ‘Eco-Obelisk’, which is not a recognised term in tree management and may I assume that this be best translated as ‘Previously Topped Tree’.
Elsewhere several of the recommendations appear to be based on terminology from the previous incarnations of the current British Standard for tree work rather than the current BS3998:2010. In particular, many of the recommended works appear to revolve around wholesale lopping or topping of tree canopies rather than the current practice of Retrenchment Pruning - a ‘form of crown reduction, intended to encourage development of the lower crown, which emulates the natural process whereby the crown of an ageing tree retains its overall biomechanical integrity by becoming smaller through the progressive shedding of small branches’. Overview - Inner (Original) Avenue. On first appearance, the historic management
of the of the original trees appears to have been at best ‘Harsh’, with the majority
of defects and management problems directly related to the poor pruning practice,
which have increased the level of risk and I assume elevated the cost and frequency
of pruning works.
A number of the trees do offer an elevated risk of harm and based upon my initial assessment two trees offer a high risk to site users and require significant remodelling or possibly removal depending upon the site management requirements. Elsewhere, twenty-six trees offer a moderate risk to site users, principally through large diameter deadwood (former topped stems), which can largely be controlled though minor remedial works - essentially the removal of deadwood. Many of the trees have had severe historical topping works undertaken, which is
not in line with either current or historic best practice and these works have
resulted in upper canopy dieback, though the majority trees are recovering from
these works.
The combination or deadwood removal and in some cases retrenchment pruning
works, would in the short to medium term enable the retention of this landscape
feature without significant investment.
A number of the trees are showing signs of stress (resulting from poor pruning),
borne out by the epicormics growths seen throughout the canopies. However, a
characteristic of this species is that it can be prone to the formation of epicormic
shoots in response to site and environmental changes. In this situation the limited
rooting volume due to the highway or historic root disturbance by compaction,
cultivation (ploughing) or trenching (services within the northern group) are
assumed to be contributory factors
The unfortunately excessive epicormics basal shoots, again a common trait for
Limes, prevents full inspection of the bases of trees for defects and possible decay
fungi – ideally assessment of the canopies of such trees should be undertaken in
late summer when health and vitality can be better assessed once the seasons
growth and stresses have taken effect.
Several of the trees have excellent habitat features for bats and perhaps owls or
other birds and these where possible should be retained in line with current best
practice and legislation.
The works specified within the original reports are generally excessive and outside
recognised standards. There is an over specification on reductions works and
typically harsh reduction. Canopy reduction should not ideally be undertaken and
instead reduction to limit wind-loading should consider the trees biology and
physiology.
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Unfortunately, the pruning recommended in the original reports is expected to
accelerate decline through further wounding and increase the spread/reinfection
of decay fungi/pathogens. The result of the recommended works is the expected
increase in risk offered by the trees and therefore potential liability. Trees are a self-
adapting system and provided good vitality is maintained they will effectively
defend internal issues and lay down wood in appropriate locations to maintain
safety. Where such areas are uneconomic for the trees to maintain they will
abandon growth leading to the formation of deadwood and potential instability
which needs to be assessed periodically as part of an ongoing assessment and
management of a tree.
Retrenchment works, when part of ongoing management, utilizes smaller diameter
pruning cuts, reducing wind loading and encourages the formation of a lower
canopy and reduces end loading and promotes growth to enable further reduction.
Removal of large sections of trees / reduction of canopies should be avoided,
occasionally it is specified but it is not suitable for the management of an avenue
already suffering from these works and is detailed within the Current British
Standard and as such is regarded Best Practice.
The specification of cutting into live wood (which has been specified within the
Whitehead report) should be kept to a minimum and ideally avoided following the
guidance of ‘Target Pruning’, the current best practice. The removal or reduction of
larger deadwood sections maybe required on health and safety grounds, but these
sections should be removed without entering into the live wood section, as new
wounds breach internal defences the tree has formed.
In general, tree removals, canopy removals or harsh reduction and remodelling
should be undertaken only with due regard for the wind loading effects of other
neighbouring trees as this can result in significant unintended consequences;
exposing trees to new environmental pressures which they have not developed to
withstand.
Overview - Outer Avenue. On first appearance, the level of suppression of the outer line is within reasonable limits with limited visual impact on the new trees form or vitality. The new trees within the outer line have benefited from previous good practice and generous planting centres. However, damage from grass cutting machinery and the potential for direct damage from the nearby fencing or cultivation works may begin to take its toll on the health of the new trees. My key finding in relation to the outer avenue are as follows:
The outer avenue of Lime trees is now becoming semi-mature in age and are on the
whole growing and developing well and only very minor suppression was noted on
these trees. A small number of trees (3No.) have basal damage the result of grass
cutting, one of which is severe and will compromise the future potential of the tree.
The general location of the trees is a concern in the medium to long term as further
growth of the trees is expected to deflect or more likely include the wire fencing
within the stem and this will require intervention - subject to ownership.
Additionally, the trees are located close to the current cultivation line (Plough Line)
of the neighbouring fields. Annual cultivation will limit rooting potential and in
combination with the presumed chemical applications, may affect the rooting
environment, causing stress and ultimately limit the potential of the trees.
All show adequate extension growth, though some would benefit from formative
pruning to remove crossing and some require sub-ordination of twin leaders. The
group would benefit from canopy lifting to avoid damage by agricultural equipment
and to provide sufficient clearance for pedestrians, this will be an ongoing
requirement of the sites management.
General Issues. Throughout the site a range of a more general tree related aspects,
which can affect the tree's condition or result in increased potential damage in the
medium to long term or complicate their future management were noted and are
discussed within the report.
BARNES & ASSOCIATES
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TABLE OF CONTENTS
Arboricultural Assessment
Page No
1 INTRODUCTION 8
2 METHODOLOGY 9
3 SITE ASSESSMENT 11
4 CONCLUSION 18
APPENDICES
A QUALIFICATIONS & EXPERIENCE
B TREE SCHEDULE & EXPLANATORY NOTES
C SITE PLANS
D FURTHER ASSESSMENTS
E TREES & RISK
Limitations of use and copyright: All rights in this report are reserved. No part of it may be reproduced or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, or stored in any retrieval system of any nature, without our written permission. Its content and format are for the exclusive use of the addressee in dealing with this site. It may not be sold, lent, hired out or divulged to any third party not directly involved in this site without the written consent of Barnes & Associates ©.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
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CTION 1 ]
ARBORICULTURAL ASSESSMENT
An assessment of the trees adjacent to publicly accessible areas. Its purpose is to provide initial information on the possible risk offered
by trees and their condition, safety and suggest either further assessment or works to improve safety. Undertaken by a qualified
arboriculturalist.
This arboricultural assessment includes general information on tree condition, value and management.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
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INTRODUCTION
1.1 The Terms of Reference. This report is based upon a ground-based
assessment and is based upon the Visual Tree Assessment (VTA)
methodology, as devised by Mattheck (1993) in addition to Hazard
Evaluation devised by Matheny & Clark (1993). Guidance is also taken
from Lonsdale (1999) Principles of Tree Hazard Assessment and
Management. The format of the survey follows the guidelines of
British Standard 5837:2012 ‘Trees in relation to design, demolition &
construction - Recommendations’ & The ISA Tree Risk Assessment
Manual (2013).
1.2 Objective. To carry out an assessment of the condition of trees and
to identify the trees, which pose a threat to site users and neighbours,
and where such trees are located propose management to enable
reasonable risk levels to be achieved. The assessment and report are
primarily aimed at reviewing the risks from the structural failure of
the trees.
1.3 Surveyor: My name is Ian Barnes; I am an Arboricultural Association
Registered Consultant, a Chartered Environmentalist, and Fellow of
the Arboricultural Association and hold the International Society of
Arboriculture Tree Risk Assessment Qualification. I have included
further details on my experience in appendix A. My area of expertise
is tree and woodland management in both urban and rural
environments. I have provided assessments of tree health, defect
analysis, tree stability, decay mapping, and the risks from falling trees
since 1990. I frequently carry out assessments and provide risk
management advice to a wide range of government, private and
commercial clients. I have based this report on my site observations
and the provided information; I have come to conclusions in light of
my experience.
1.4 The scope of this report: This preliminary assessment is concerned with
the health and risk offered by the trees, in addition comments relating
to general management requirements are included; remedial
recommendations are included.
1.4.1 The statements made in this report do not take account of the effects
of extremes of climate, vandalism or accident, whether physical,
chemical or fire. Barnes & Associates cannot therefore accept any
liability in connection with these factors, nor where prescribed work is
not carried out in a correct and professional manner in accordance
with current good practice. The authority of this report ceases at any
stated time limit within it, or if none stated after two years from the
date of the survey, or when any site conditions change, or pruning or
other works unspecified in the report are carried out to, or affecting,
the Subject Tree(s), whichever is the sooner.
1.4.2 Assessment of the potential influence of trees upon buildings or other
structures resulting from the effects of trees abstracting water from
shrinkable load-bearing soils was not included in my instruction and is
not considered here.
1.5 Tree Tags: The trees have been previously tagged.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
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METHODOLOGY.
2.0 Potential Risk from Trees. Trees, unlike built structures are a dynamic structure and
offer several specific management issues that need to be considered. Reasonable risk
management generally aims to provide trees that can be regarded stable in a normal
/ foreseeable, storm event.
2.1 Wind Speed. In general, the windiest parts of the UK are the north and west. This is
because the prevailing west to south-westerly winds across the UK lead to northern
and western areas being typically more exposed than the south and east.
2.1.1 There are also a lot of
localized effects with most
hills, mountains and coasts
being windier than low-lying
inland areas. Wind speed
increases as you go upwards
away from the friction caused
by the earth's surface. This
also explains the windier
coasts as the sea surface
produces less friction than
the land.
2.1.2 In this region, we expect to
receive peak wind speeds
around of 22 to 24 m/s based
upon information published
in the UK National Annex to
Eurocode 1 - Actions on
structures Part 1-4: General
actions - Wind actions. This
equates to a force 9 Strong
Gale on the Beaufort Wind Scale. I have included further general information upon the
Tree & Risk in - appendix E.
2.2 Target evaluation. To enable a balanced approach to the site assessment I undertook
an initial assessment of the associated risks on site to identify areas of high public
access, areas where trees are within striking range of valuable or fragile structures or
high human occupancy locations. Targets are broadly zoned in the ’Target’ ranges
based on the levels of occupation, population and value. These were assumed to be
generally low target areas with the site having occasional to frequent occupation.
2.3 Risk Assessment. The assessment follows the general principles of Risk Assessment;
Risk assessment is important to reduce the risk of injury to people, property damage
or disruption of services. The International Society of Arboriculture (ISA) Tree Risk
Assessment Methodology takes a qualitative rather than quantitative approach to risk
assessment. The system uses the output of matrix 1 (copied below) to compare the
likelihood of failure of a tree or tree part, the likelihood of impacting the target and
the potential consequences of failure.
2.4 The matrices generate an output in matrix 2 (above), describing the risk offered by the
trees in line with general risk assessment methodologies; these are arranged into
bands differentiated by coloured text within the tree schedule. Highlighted above are
the colours representing the risk band of indices.
Matrix 1. Likelihood of failure
Likelihood of failure
Likelihood of Impacting Target
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
Matrix 2. Risk Rating matrix
Likelihood of failure & impact
Consequences of Failure
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
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2.5 The UK Health and Safety Executive (Anon. 2001) suggests that "an individual risk of
death of one in a thousand per annum should on its own represent the dividing line
between what could be just tolerable for any substantial category of workers for any
large part of a working life, and what is unacceptable for any but fairly exceptional
groups. The Tolerability of Risk framework (ToR) (HSE 2001) is a widely accepted
approach to reaching decisions on whether risks are broadly acceptable,
unacceptable, or tolerable.
2.6 In respect of trees, some risks cross the Broadly Acceptable 1/1,000,000 boundary,
but remain tolerable. This is because any further reduction would involve a
disproportionate cost in terms of the lost environmental, visual, and other benefits, in
addition to the financial cost of controlling the risk. For members of the public who
have a risk imposed on them ‘in the wider interest of society’ this limit is judged to be
an order of magnitude lower – at 1 in 10, 000 per annum." Furthermore, “HSE believes
that an
2.7 individual risk of death of one in a million per annum for both workers and the public,
corresponds to a very low level of risk and should be used as a guideline for the
boundary between the broadly acceptable and tolerable regions” as demonstrated in
the table opposite.
2.8 Importantly, to enable tree assessors to provide appropriate management guidance,
it is helpful to have some understanding of the tree owner’s management preferences
prior to assessing the trees.
2.9 Barnes & Associates can offer guidance on but cannot set the threshold of risk at which
you manage your trees. We consider in line with normal health and safety guidelines
that 1 in 10,000 an appropriate level and I have formulated management proposals
on this basis.
2.10 The Advisory Risk Threshold provides information upon priority with trees with the
highest risk rating with the greatest target values requiring work urgently. Where the
priority of trees is recorded as being low and a low target value, works required to
improve the trees risk of harm, are expected to be undertaken as part of the normal
estate management.
Advisory Risk Thresholds
Thresholds Description Action
Unacceptable Risks will not ordinarily be tolerated
Control the risk
1/1 000
Unacceptable (where imposed on others) Risks will not ordinarily be tolerated
Control the risk
Review the risk
Tolerable (by agreement) Risks may be tolerated if those exposed to the risk accept it, or the tree has exceptional value
Control the risk unless there is broad stakeholder agreement to tolerate it, or the tree has exceptional value
Review the risk
1/10 000
Tolerable (where imposed on others) Risks are tolerable if ALARP
Assess costs and benefits of risk control
Control the risk only where a significant benefit might be achieved at reasonable cost
Review the risk
1/1 000 000 Broadly Acceptable Risk is already ALARP
No action currently required
Review the risk
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
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SITE ASSESSMENT 3.1 Date of Inspection. 10th & 20th May 2016.
3.2 Weather conditions. The weather was bright with good visibility.
3.3 Boundaries: The site boundaries are well defined by fencing.
3.4 Tree Population. The trees compose of a mature central avenue of trees
located in the highway verge and a maturing outer avenue of trees.
3.5 Principal Targets. The trees are located close to the highway (The Avenue )
& an informal footpath that travels roughly east - west between the inner
and outer trees and these are assumed to be the principal targets.
3.6 Pedestrian Access. Pedestrian access is possible around the site, though
access appears to be concentrated on the well-defined footpath network
and is assumed to be limited to reasonable weather conditions.
3.7 Vehicle Access. Vehicle access although within the national speed limit the
junction at the western end of the site and the bend, and 30mph limit at the
eastern end, in addition to the presence of the trees which appears to limit
the speed of vehicles, which is expected to limit the potential for impact.
3.8 Condition of Trees. This inspection provides an initial assessment of the
principal trees, within the existing site along with landscape and
environmental constraints.
3.8.1 The trees have been assessed from ground level only. Information upon the
trees is located in the Tree Schedule in appendix B.
3.9 Identification and location of the trees. I have illustrated the location of the
recorded trees on the site plans included and referenced BA5446/A. A
numbered copy is included in - appendix C. Trees are shown on the plan,
which is for illustrative purposes only and should not be used for directly
scaling measurements.
3.10 My information is loosely based upon the information within the various
A.Whitehead Associates Ltd reports and I have adopted the same numbering
methodology to avoid any confusion.
3.11 Visual assessment of trees. The assessment of the trees was undertaken
from ground level using Visual Tree Assessment (VTA), this is a non-invasive
method of examining the health and structural condition of individual trees.
The assessment provides information on the condition of the roots, trunk,
main branch structure, crown, buds and leaves together providing an
assessment of general tree health and vitality.
3.12 Basic decay detection tools such as a Nylon Mallet & Steel Probe were
utilised to determine whether further investigation is required, using more
invasive methods.
3.12.1 Other than where the height of a tree is critical to the outcome of the
assessment, approximately 1 in 10 trees are measured using a clinometer
and the remainder estimated against the measured trees. Where possible
canopies are measured using either a tape or measuring wheel, where
access is restricted, they are estimated. Stem diameters are measured using
a rounded down diameter tape to avoid variations due to stem shape,
otherwise where trees are in a group and / or not accessible the stem’s
mean stem diameters are estimated to provide a reasonable basis for tree
protection.
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3.13 Problem trees. The Lime T103 offers a High Risk, through the potential failure
of the main stem which requires urgent closer assessment. The tree as with
many of the trees in the line have been historically topped, resulting in a
series of tightly developing ascending main leaders. One of these appears to
have failed naturally and one appears to have been removed, leaving an
upright secondary leader supported by a main stem affected by localised
decay as shown below. The stem, which has a marked hollow is unlikely to
recover leaving the stem predisposed to failure.
3.13.1 Tree T103, has good overall vitality, and is redeveloping a secondary lower
stem which could be maintained at little cost to provide continuity, maturity
to the line in addition to valuable biodiversity in the form of a developing
hollow.
3.13.2 An additional Lime T127 offers a High Risk, through potential failure of the
dead main stem, the result of historically topping works as shown below.
The stem, which has a marked hollow is unlikely to recover leaving the
stem predisposed to failure.
3.13.3 Tree T127, has good overall vitality, and is redeveloping a secondary lower
stem which could be maintained at little cost following removal of the dead
section to provide continuity, maturity to the line.
3.13.4 In addition, to the high risk trees a further 26 trees offer a Moderate Risk of
harm to both highway and footpath. Information upon these trees is located
in the Tree Schedule in appendix B, though in general the risk offered by
these trees is the result of large diameter deadwood formation resulting
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from harsh historic works that have centred around topping and lopping.
These works have caused canopy decline, topping and lopping are
considered out of date practices. The general vitality of the trees indicates
good recovery and suggests that they have sufficient resources to develop
compensatory adaptive growth as the secondary canopy develops.
3.13.5 Several trees at the western end of the group principally the Ash
T135(shown below) & T136 have some canopy asymmetry as a result of
additional light levels and increased exposure to prevailing winds,
although by virtue of their location do provide a valuable wind break and
help shelter the remainder of the group. These trees will require careful
remodelling to balance the risk offered by branch failure with the level of
shelter that they provide for the remaining group. By way of an example I
have indicated the likely level of branch reduction with the red line on the
photograph below.
ARBORICULTURAL ASSESSMENT
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3.14 General Site Issues. Whilst on site a range of general arboricultural issues
were seen which have the potential to affect the development of trees and
may result in future problems or which may result in elevated management
costs for the site in the future.
3.14.1 Trees throughout the site appear to be in a reasonable state in light of their
current maturity, recent localised changes and as a result of historic
management.
3.14.2 Direct damage to structures, several trees are located close to the bridge at
the NE of the site and are expected to cause direct damage through
deflection resulting from further growth. As indicated on the photograph
below. Ideally this structure should more closely assessed or the trees
removed to protect the feature.
3.14.3 Ivy is developing through a number of the
trees, throughout the site. It has a variety of
conservation benefits. However, if left
unmanaged it may be considered unsightly
and more importantly, can create problems
for efficient management by obscuring
structural defects and may increase the
weight of a tree's crown and the 'sail' effect
during the wet windier winter months –
Ideally this should be controlled throughout
the site.
3.14.4 Trenching, a service of
unknown age and depth
is located between the
inner and outer line of
trees indicated by the
dashed line on the
photograph opposite.
This is expected to have
caused localised root
severance, compaction
and potentially soil level
changes and could be
related to the decline of trees, which increases the chances of deadwood or
failures due to pathogens. Ideally, these aspects should be monitored locally.
In particular, trees can become susceptible to colonisation with Honey
Fungus, which can readily breach defences in the stem versus the roots.
Ideally, in this situation the soil close to the stem should be removed to the
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
Page 15 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
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original soil depth using an ‘Air Spade’ to a distance of 3 times the stem
diameter and the void filled with a porous material such as gravel or perlite
to avoid a trip hazard.
3.14.5 Compaction, affects to the soils between the inner and outer lines of trees
the result of both vehicle activities, horses and pedestrians. This damage has
the potential to restrict the development and efficiency of roots. Ideally,
following works to
improve the
rootzone, the area
should be mulched
to restrict the
development of
competing weed
species, to increase
the soils organic
content helping to
mimic the conditions
found in a natural
woodland. Ideally, access to the site particulate during wet periods should be
limited.
3.14.6 Most plants form mycorrhizal associations with fungi which live in the soil.
Mycorrhizal fungi benefit trees by linking directly with tree roots to provide
the equivalent of an extended root system. They gather essential nutrients
otherwise inaccessible to the tree and act as a barrier to certain disease-
causing organisms. These organisms may enter the tree if fertilisers and
chemicals encourage the growth of non-mycorrhizal roots. Mycorrhizae help
the tree to cope with extremes in growing conditions. However, they are
sensitive to compaction, prolonged periods of waterlogging or drying out in
summer and inorganic chemicals such as fertilizers or herbicides and as such,
these should be avoided wherever possible.
3.14.7 Low tree canopies, are
affecting pedestrian
access, and are
developing into the
highway, with some
trees having evidence
of damage from high
sided vehicles. The
tree canopies should
ideally be lifted to 2.5
metres above the
footpath and 5.2
metres above the carriageway to avoid damage to both the trees and
vehicles.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
Page 16 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
3.14.8 Tree Guards are
located close to many
of the younger trees, if
retained too long this
can cause direct
abrasion damage to
stem and lower
branches, ideally
guards should be
removed / relocated
before they impact the
trees they are
protecting.
3.14.9 Adaptive Growth - Trees are dynamic structures that economically transfer
their own weight and any additional forces such as wind and weather,
through a network of branches into the main stem to the root which in turn
transfers the force into the local supporting soils, through ever-changing
Tension & Compression within the wood of the tree; described as the ‘Axiom
of uniform stress’. Initially defined in the Body Language of Trees by Claus
Mattheck and Helge Breloer (which has now been refined into the system
commonly known as ‘Visual Tree Assessment’ (VTA)) as "the tendency for all
self-optimizing structures to make as economic a use of their material as
possible, and to become as strong as necessary to perform their function",
as indicated by the ribbing below the codominant leader on the tree shown
opposite.
3.14.10 Topping, often removes 50 to 100 percent of the leaf-bearing crown of a tree.
Because leaves are the food factories of a tree, removing them can
temporarily starve a tree. The severity of the pruning triggers a sort of
survival mechanism that causes a tree to produce multiple shoots below each
topping cut and comes at great expense to the tree. These shoots develop
from buds near the surface of the old branches. Unlike normal branches that
develop in a socket of overlapping wood tissues, these new shoots are
Included union
Adaptive growth
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
Page 17 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
anchored only in the outermost layers of the parent branches. The new
shoots grow quickly, as much as 3 meters in one year, in some species.
Unfortunately, the shoots are prone to breaking, especially during windy
conditions. The irony is that while the goal was to reduce the tree’s height to
make it safer, it has been made it more hazardous than before and as a result
tree requires periodic assessment and intervention.
3.14.11 Structural Issues, many tree species are susceptible to the formation of tight
of included unions. Usually, indicated by a V-shaped fork. This is a serious
hazard for several reasons. Where the bark is between the stems, the tree
will never be able to bind the stems together by fusing the tissues. Included
bark often remains alive and growing. As the stems grow in diameter, they
force the fork apart. The point below, where the two stems are really joined,
is unable to adjust to this pressure and tends to crack. Such unions are
observed on site both and as shown above, within both the inner and outer
line and should ideally be improved through formative pruning.
3.14.12 Suppression, the development of the outer line of trees appears to be largely
normal with only minor
deviation of form or
deflection of stems being
observed. This is assumed
to be largely a benefit of
the good foresight of
providing good
separation distances
(typically around 8
meters) at planting.
Providing current growth
is maintained the outer
line is expected to achieve a similar height as the inner line and provide
shelter in the medium term.
3.14.13 Available Space, due to the very close
cultivation line (Plough Line) within
the neighbouring fields shown
opposite on the aerial image,
downloaded and used courtesy of
©Google and ©third-party suppliers
notated on the image. Annual
cultivation is expected to damage
rooting and in combination with
chemical applications may affect the
rooting environment for trees
negatively and ultimately limit the
potential of the trees.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
Page 18 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
CONCLUSION
4.0 Generally, the trees are in good condition and appear to have good vitality.
4.1 Tree Management. The site would benefit from an improvement in the level
of and frequency of tree assessment. This increase in the level of
management would not only help improve the day to day level of safety, but
would provide the range of benefits offered by the trees.
4.1.1 Ideally, a management plan should be prepared to help provide a more
detailed insight into the population of the trees. To provide appropriate
forthcoming works, planting opportunities and to help identify both
immediate and ongoing management to help stabilise the tree population.
4.1.2 In addition to this, there are opportunities to help provide additional trees
through the establishment of replacement trees or the improved
management of natural regeneration.
4.1.3 Trees potentially live for many generations their environment and people’s
attitudes can change significantly over their life spans, and management
practices can change. Plans and procedures should be reviewed regularly to
ensure they remain effective and current, particularly in relation to climate
change issues.
4.2 Additional Assessment. A number of trees require more detailed assessment
to understand the internal condition of the stem and or branches and this is
detailed in appendix C.
4.3 Remedial Tree Works. A number of trees contain defects and require works
to improve their condition. These works are detailed within the tree schedule
listed in appendix B. Once these have been undertaken the issues related to
tree damage can be better understood.
4.4 Additional and ongoing Requirements. The site will require ongoing
assessment to maintain a reasonable level of safety. I have included an
outline of further assessments within appendix D, with information upon the
preferred time scales. I can send a budget for this if required.
4.5 Limiting Site Access. It is reasonable to assume a ‘Storm’ of force 10 using the
Beaufort Scale (55 - 63 miles per hour of wind speeds on land) will occur
annually and such a risk should be built into the site management. Recent
work has shown even sound trees that would typically be regarded as safe
can fail during high winds through various factors relating to wood
physiology, dynamics and the relationship between the root system and the
supporting soils.
4.5.1 Typically, trees have evolved to fail in part, i.e. twigs and branches are
sacrificed / fail from a parent tree rather than the tree being lost entirely.
Observations at various sites have found that twigs and branches, can break
from trees at wind speeds of as little as 31 miles per hour, the upper limit of
a ‘strong breeze’ as detailed in Beaufort Scale 6 (25 - 31 miles per hour).
4.5.2 Such branch failures are difficult to predict with any great level of detail and
as such, I would recommend a defensive position is best adopted. In light of
this, I would suggest that changes to the opening arrangements are
considered and that access to the site is restricted when the wind speeds
approach 'Near Gale' or ‘Moderate Gale’ - Beaufort Force 7, 32-38 miles per
hour or 30mph based upon normal broadcast weather forecasts.
ARBORICULTURAL ASSESSMENT
BARNES & ASSOCIATES
Page 19 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
4.5.3 However, in light of the access requirements, this is not always achievable
and instead management to improve safety is the only realistic alternative.
4.6 Trees subject to statutory controls. If the trees are covered by a tree
preservation order or located in a conservation area or other legal planning
constraint works may be restricted. The works specified within this report
are necessary for reasonable management and should be acceptable to the
local authority.
4.7 Implementation of works. I would always suggest that you get at least three
fixed price quotations before deciding upon a contractor to undertake the
works on your behalf. If required, I can prepare a detailed breakdown of the
works for tendering purposes. Work schedules can also be supplied including
an appropriate technical specification for the various arboricultural and
horticultural operations.
4.7.1 You should ensure that any contractor employed for the above works is
suitably qualified and experienced, familiar with current best practice and
covered by current, public, products, and employee liability insurance, to an
adequate level. I would advise that any Arboricultural work is carried out by
a reputable contractor from the local authority list if available, or
alternatively one approved by the Arboricultural Association
(www.trees.org.uk) or Trustmark (www.treecareapproved.org).
4.7.2 The contractor should carry out all tree works to BS3998 (2010) Tree Work –
Recommendations and/or the European Tree Pruning Guide - European
Arboricultural Council (English Version) and the Industry Code of Practice for
Arboriculture: Tree Work at Height (Edition 1, February 2015). Works should
be undertaken in strict accordance with current arboricultural best practice
ensuring that any pruning works accord with current target pruning
methodology. They should be fully conversant with current Arboricultural
best practice and adhere to all relevant legislation including the New Road &
Street Works Act 1991 for works in proximity of highways, and The Working
at Heights Regulation 2005. In addition to the dangers & legislation associated
with working close to Electrical Supplies.
4.7.3 Additionally, they should be aware of the Wildlife and Countryside Act 1981.
In addition, the amendments of 1991 and its implications to tree works.
Works should be planned to avoid times when birds are nesting, and be
aware that a bat survey may be needed on significant tree hollows. If bats
are discovered during inspection or subsequent work, English Nature must
be informed immediately.
4.8 Legal Duty. Tree owners have a statutory duty of care under the Health and
Safety at Work Act 1974 and the Occupiers Liability Acts of 1957 & 1984 to
ensure that members of the public and staff are not to be put at risk because
of any failure by the owner and to take all reasonable precautions to ensure
their safety.
4.8.1 A risk assessment is required under the Management of Health and Safety
Regulations 1999. There is a need to inspect trees in or near public places, or
adjacent to buildings or working areas to assess whether they represent a
risk to life or property, and to take remedial action as appropriate.
4.9 Future considerations. Trees are living organisms whose health and condition
can change rapidly. The health, condition and safety of trees should be
checked on a regular basis. In addition to the professional inspection, a tree
owner should inspect their trees personally on a regular basis, in particular
after stormy weather and high winds.
APPENDICES
Barnes & Associates
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APPENDICES
APPENDICES
Barnes & Associates
Page 21 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
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APPENDIX A – BRIEF QUALIFICATIONS AND EXPERIENCE OF IAN BARNES Registration Schemes:
Arboricultural association Registered Consultant (49)
Qualifications:
Higher Diploma in Arboriculture (H.N.D Arb)
National Diploma in Horticulture & Arboriculture (N.D.Ht/Arb)
Arboricultural Association Technicians Certificate (Tech.Cert. (Arbor.A))
International Society of Arboriculture – Tree Risk Assessment (TRAQ)
Membership grades by peer review:
Chartered Environmentalist (CEnv)
Corporate Member Institute of Horticulture (MI Hort)
Fellow of the Arboricultural Association (F.Arbor.A)
Professional member Consulting Arborist Society UK.
Practical experience:
I have worked in the Arboricultural Industry since 1987. Firstly as a climbing Arborist in both the public and private, sector, undertaking a wide range of practical operations
on a variety of sites, before becoming a gang foreman. I set up and ran my own Arboricultural contracting business for 15 years, though this is now under new ownership. I
have developed an arboricultural consultancy practice since 1993, working throughout England for clients in both the public and private sector.
Continuing professional development:
As part of my ongoing education, I am a member of a range of related Arboricultural bodies. Including the Arboricultural Association (AA), International Society of
Arboriculture (ISA), Royal Forestry Society (RFS), Forestry Contracting Association (FCA), and Consulting Arborist Society (CAS) of which I am a professional member. I am a
corporate member of the Institute of Horticulture (MI Hort) and a Fellow of the Arboricultural Association (F.Arbor.A). An inclusive member of the British Mycology Society (BMS)
in addition to being a Chartered Environmentalist (CEnv).
I am a registered consultant of the Arboricultural Association. I regularly attend seminars and training events on issues relevant to Arboriculture these include events focusing
on General Tree Management, Veteran Tree Management, Tree Health, Tree Pest management, Tree Diseases management, Trees Biology & Morphology, Tree Stability, Wind
Loading of Trees, Tree Risk Assessment, in addition to keeping an upto date level of CPD.
I am a licensed user of the Quantified Tree Risk Assessment (QTRA) System and regularly attend updates. I am a trained user of Picus ‘Acoustic’ Tomography and have
attended training to extend my knowledge in this area. I am trained in the use of thermal imaging as an aid to detecting defects in trees.
Relevant experience:
My career to date has involved me in a variety of tree care, dealing with trees in many different environments, and with differing management aims, these included: Tree
planting schemes, including Woodland Design & Management, Detailed Health and Safety Appraisals, Tree inventories / population surveys, Management & selection on
both proposed and active development sites, Advice upon trees in relation to structures, Additional areas of work such as Contract Specification & Management, Planning
applications, Expert Witness.
This has provided me with a range of experience, enabling me to comment upon trees and their management, in line with current best practice. Full CPD and training record
can be forwarded upon request.
APPENDICES
Barnes & Associates
Page 22 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
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APPENDIX B – TREE SCHEDULE & EXPLANATORY NOTES The following survey has been prepared from a visual assessment taken from ground level without any detailed investigation. Observations are based upon the body language of the trees and any visual indicators present at the time of inspection. This survey should be regarded as a preliminary overview; ongoing inspections will be required as specified individually. In most situations the health, condition and safety of trees should be checked on a cyclic basis, alternating between early and late seasons to ensure a full picture of tree health is established. Inspections should only be carried out by a suitably qualified arborist. Similarly, numerous potential defects may not be detectable dependent upon timing of inspection, in particular, wood decay fungi, which may only occasionally produce external fructifications annually (rather than perennially), or may not provide external symptoms until an advanced state is achieved. Reasonable risk management generally aims to provide a tree that can be regarded stable in a normal / foreseeable, regularly experienced storm events i.e. force 10 storms. The level of risk offered by the tree will be significantly greater as the wind speed that the tree is exposed to increases beyond this level. Additionally the threat from aerial parts i.e. Tight unions may remain even following works, although failures of such parts are likely to be limited to small diameter branches and to periods of extreme weather. As an arborist, I am a tree specialist and use my knowledge, education, training and experience to examine trees, recommend m easures to enhance their beauty and health, and attempt to reduce the risk of living near trees. As a client, you may choose to accept or disregard these recommendations, or seek additional advice. As an arborist I cannot detect every condition that could possibly lead to a tree or limb failure. Trees are living organisms that may fail in many ways, some of which we do not fully understand. Conditions are often hidden within the tree and below the ground. As arborists, we cannot guarantee that a tree will be healthy or safe under all circumstances, or for a specified period of time. Sometimes trees may appear "healthy," but may be structurally unsound. Likewise remedial treatment, like any medicine, cannot be guaranteed. Treatment, pruning and removal of trees may involve considerations beyond the arboricultural perspective, such as property boundaries and ownership, disputes between neighbours, planning issues, sight lines, landlord-tenant matters etc. Arborists cannot take such issues into account unless complete and accurate information is given to them. Likewise, as an arborist I cannot accept any responsibility for the authorization r non-authorization of any recommended treatment or remedial measure. Furthermore, certain trees are borderline cases as to whether they should remain or be removed. If conditions change a tree may need further monitoring in the future to determine its health and structure. Trees can be managed, but they cannot be controlled, and to live near a tree is to accept some degree of risk. Mathematical abbreviations: > = Greater than, < = Less than. Measurements / estimates: All dimensions are estimates unless otherwise indicated. Measurements taken with a tape or clinometer are indicated with a ‘#’. Less reliable estimated dimensions are indicated with a ‘?’. Tree number: Numbered Tag attached to each stem usually on the inside face of the stem at roughly 2.5 metres. Where the number is followed by a C or G this demotes that the tag refers to a Compartment or Group. Name: Tree species are detailed by their common name- Latin ca ne provided upon request. Age: I record the age as an estimate of the tree likely span for guidance only i.e: Y Young Recently established/planted tree. SM Semi Mature Fully established and growing with high vigour EM Early Mature The first third of its likely expected life span M Mature The middle one third of its likely expected life span
EOM Early Over Mature Clear reduction in vitality, typically small deadwood early canopy retrenchment. OM Over Mature The later one third of its likely expected life span with sign of canopy retrenchment. V Veteran An aged example of the species, typically with defects & conservation value S Senescent Beyond its expected Life span possible of historical interest or in a state of decline
Height: I estimate height to the nearest metre to the mean height. Height to underside: I estimate height to the nearest half metre to the mean underside of the canopy. Diameter: These figures relate to a measurement of the stem at 1.5m above ground level recorded in millimetres, measured with a rounded down diameter tape. Figures prefixed with MS denote trees or shrubs with multiple stems. Canopy (N S E W): I estimate the distance of the canopy radius to the nearest metre to provide a mean distance of separation between the stem and the outer canopy.
APPENDICES
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Page 23 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
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Vitality: Is a personal assessment of the tree's growth rate in the current season, in comparison to other trees within the locality, region and an indicator of the tree likely response to site change. D - Dead A dead or very low vitality tree L - Low / Declining A tree in noticeable poor state N - Normal A tree of typical vitality P - Poor A tree of low vitality F - Fair A tree of lower vitality G - Good A tree of high vitality Safe Life: Is a personal assessment of the trees likely expected remaining safe life span in years, assuming the site management continues as it i s at present or the tree is protected from significant environmental change. Trees can reverse even enter into serious decline with site changes, likewise the expected safe life can be significantly improved following changes / improvements to site management and following remedial works. 40 or more Good vitality a tree a tree with high potential. 10 to 20 Early reduction in vitality / reducing foliage cover. 5 or less Serious decline or very low vitality tree 20 to 40 Normal vitality a tree in good health. 10 or less Marked decline / reduced foliage cover. 1 or Less A dead or almost dead tree with very low vitality tree Category: I included a method-adopted form BS5837 to enable rapid assessment of a trees quality detailed below.
Comments / Observations: General comments referring to tree health, structure and condition. Management Options: Comments detailing remedial works required improving immediate safety or improve the management of the tree. Priority: Guidance for the time scale in which works should be completed, from the date of the report. Tree Risk Assessment: The International Society of Arboriculture (ISA) Tree Risk Assessment Qualification (TRAQ) takes a qualitative rather than quantitative approach to risk assessment. It uses matrices to compare the likelihood of failure of a tree or tree part, the likelihood that it will impact the target and the potential consequences of failure. Unless stated otherwise the risk assessment assumes the risk offered Over the next year.
Category and definition Criteria (including subcategories where appropriate) Colour Code
Trees unsuitable for retention (see Note)
Category U Trees that cannot realistically be retained as living trees in the context of the current land use for longer than 10 years
Trees that have a serious, irremediable, structural defect, such that their early loss is expected due to collapse and are not expected to respond to pruning. Trees that are dead or are showing signs of significant, immediate, and irreversible overall decline or infected with pathogens of significance to the health NOTE Category U trees can have existing or potential conservation value, which it might be desirable to preserve though canopy reduction or removal.
Red on Plan
s Trees to be considered for retention
1 Mainly arboricultural qualities 2 Mainly landscape qualities 3 Mainly cultural values, including conservation
Category A Trees of high quality with an estimated remaining life expectancy of at least 40 years
Trees that are particularly good examples of their species, especially if rare or unusual; or those that are essential components of groups.
Trees, groups or woodlands of particular visual importance as arboricultural and/or landscape features
Trees, groups or woodlands of significant conservation, historical, commemorative or other value (e.g. veteran trees or wood-pasture)
Green on Plan
Category B Trees of moderate quality with an estimated remaining life expectancy of at least 20 years
Trees downgraded because of impaired condition, or having remediable defects, such as unsympathetic past management or damage.
Usually growing as groups or woodlands, such that they attract a higher collective rating than they might as individuals
Trees with material conservation or other cultural value Blue on
Plan
Category C Trees of low quality with an estimated remaining life expectancy of at least 10 years, or young trees with a stem diameter below 150 mm
Unremarkable trees of very limited merit or such impaired condition that they do not qualify in higher categories
Trees present in groups or woodlands, Trees with no material conservation or other cultural value Grey on
Plan
Matrix 1. Likelihood of failure
Likelihood of failure
Likelihood of Impacting Target
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
Matrix 2. Risk Rating matrix
Likelihood of failure & impact
Consequences of Failure
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
APPENDICES Barnes & Associates
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Preliminary Arboricultural Assessment - This should not be referred to as a specification of Arboricultural Works.
Tag No. Species
Ag
e
He
igh
t
He
igh
t to
c
an
op
y
No
rth
So
uth
Ea
st
Wes
t
Vit
ali
ty
Sa
fe L
ife
Ca
teg
ory
Ste
m D
ia
(mm
)
Observations Risk
offered by tree
Target Assessment
Management options Priority for
Action
Risk offered
following Works
T101 Common
Lime M 15 4 4 4 5 4 Fair 20+ C2 700
Compaction by vehicles within in rootzone. Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Cavities are visible within the main branches. Woodpecker hole suggests a volume of decay.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T102 Large-leaved Lime
M 24 4 8 8 5 5 Fair 20+ C2 1000
Compaction by vehicles within in rootzone. Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Cavities are visible within the main branches. Branch failures are visible within the canopy. Woodpecker hole suggests a volume of decay.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Retrench the canopy in stages to create a smaller canopy by a maximum of 1.5M. Crown lift to 5.2m to enable vehicle access. or Consider veteran management to retain the stem and provide habitat.
<1 year
Low
T103 Large-leaved Lime
M 20 4 9 8 5 5 Fair <10 C2 1000
The stem has a significant structural issue. Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Cavities are visible within the main branches. Branch failures are visible within the canopy. Wounding from branch failures can be seen within the outer canopy. Significant asymmetry to the canopy. Elongated branches visible within the canopy. High-end loading can be seen on branches. Branches are predisposed to failure. Poor final pruning cuts throughout the canopy. Canopy has been reduced (topped) & redeveloped.
High
Canopy overhangs the highway and pedestrian
access.
Canopy remodelling to reduce canopy volume. Retrench the canopy in stages to create a smaller canopy by a maximum of 1.5m. or Consider veteran management to retain the stem and provide habitat. or Remove and grind the stump. Establish a replacement tree elsewhere.
<3 months Low
T107 Common
Lime M 12 4 4 4 4 4 Fair 20+ C2 600
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T111 Large-leaved Lime
M 13 4 6 4 4 4 Fair 20+ C2 700
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Elongated branches visible within the canopy. Poor final pruning cuts throughout the canopy. The canopy has been lopped recently and likely to develop a poorly formed canopy. Canopy has been over pruned significantly. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Canopy remodelling to reduce the lower northern canopy volume. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T118 Common
Lime M 16.5 4 5 5 5 5 Fair 20+ C2 700
Small cavity visible within the main stem. Hollows in the stem at 3m & 4m. Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Branch failures are visible within the canopy. Wounding from branch failures visible. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Ideally - Undertake Tomography of noted fault.at 3.5m Remove large deadwood only. Canopy remodelling to reduce canopy volume required. Crown lift to 5.2m to enable vehicle access.
<6 months Low
T119 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Small hollow visible in the main stem. Large deadwood can be seen in the outer canopy. Hollows in the stem at 3m & 4m.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access. Undertake Tomography of noted fault.at 4m.
<1 year Low
APPENDICES Barnes & Associates
Page 25 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
Preliminary Arboricultural Assessment - This should not be referred to as a specification of Arboricultural Works.
Tag No. Species
Ag
e
He
igh
t
He
igh
t to
c
an
op
y
No
rth
So
uth
Ea
st
Wes
t
Vit
ali
ty
Sa
fe L
ife
Ca
teg
ory
Ste
m D
ia
(mm
)
Observations Risk
offered by tree
Target Assessment
Management options Priority for
Action
Risk offered
following Works
T120 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T121 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T124 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T127 Large-leaved Lime
M 11 4 4.5 4.5 4.5 4.5 Fair <10 C2 600
The stem has a significant structural issue. Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Branch failures are visible within the canopy. Wounding from branch failures can be seen within the outer canopy. Branches are predisposed to failure. Poor final pruning cuts throughout the canopy. Canopy has been reduced (topped) & redeveloped.
High
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Consider veteran management to retain the stem and provide habitat.
<1 year Low
T131 Common
Lime M 15 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T132 Common
Lime M 15 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T134 Common
Lime M 15 4 4.5 4.5 4.5 4.5 Fair 20+ C2 600
Single stem with buttress shooting. Large deadwood can be seen in the outer canopy.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T135 Common
Lime M 20 4 9 7 7 7 Fair 20+ C2 800
Significant quantities of deadwood can be seen within the canopy. Crown distorted due to group pressure. Significant asymmetry to the canopy. Elongated branches visible within the canopy. Branches are predisposed to failure.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Retrench the canopy in stages to create a smaller canopy. Crown lift to 5.2m to enable vehicle access. Reduce canopy spread overall by 2m in the NE canopy. Reduce branches extending outside the canopy line by 1.5m. or Consider veteran management to retain the stem and provide habitat.
<1 year Low
APPENDICES Barnes & Associates
Page 26 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
Preliminary Arboricultural Assessment - This should not be referred to as a specification of Arboricultural Works.
Tag No. Species
Ag
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(mm
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Observations Risk
offered by tree
Target Assessment
Management options Priority for
Action
Risk offered
following Works
T136 Common
Lime M 20 4 6.5 6.5 6.5 6.5 Fair 20+ C2 800
Significant quantities of deadwood can be seen within the canopy. Cracking visible in branches in the outer canopy. Hazard beam can be seen within the canopy. Crown distorted due to group pressure. Significant asymmetry to the canopy. Elongated branches visible within the canopy. Branches are predisposed to failure.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Retrench the canopy in stages to create a smaller canopy by a maximum of 1.5m. Reduce branches extending outside the canopy line by 1.5m. Crown lift to 5.2m to enable vehicle access. or Consider veteran management to retain the stem and provide habitat.
<1 year Low
T139 Common
Lime M 12 4 5 5 5 5 Fair 10+ C2 800
Medium cavity visible within the main stem. Significant quantities of deadwood can be seen within the canopy. Crown distorted due to group pressure. Significant asymmetry to the canopy. Elongated branches visible within the canopy. Branches are predisposed to failure.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Retrench the canopy in stages to create a smaller canopy by a maximum of 1.5m. Reduce canopy overall by 2m limit branch end loading.2.5m to S. Consider veteran management to retain the stem and provide habitat. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T144 Common
Lime M 20 4 6.5 6.5 6.5 6.5 Fair 20+ C2 900 Large deadwood can be seen in the outer canopy. Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T146 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 750 Large deadwood can be seen in the outer canopy. Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T147 Common
Lime M 11 4 4.5 4.5 4.5 4.5 Fair 20+ C2 750 Large deadwood can be seen in the outer canopy. Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T149 Common
Lime M 20 4 5.5 5.5 5.5 5.5 Fair 20+ C2 750 Large deadwood can be seen in the outer canopy. Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Canopy remodelling to improve shape. Retrench the canopy in stages to create a smaller canopy. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T151 Common
Lime OM 6 3 4 4 4 4 Fair 20+ C2 450
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T152 Common
Lime OM 11 3 4 4 4 4 Fair 20+ C2 500
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T156 Common
Lime M 17 3 5.5 5.5 5.5 5.5 Fair 20+ C2 600
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
APPENDICES Barnes & Associates
Page 27 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
Preliminary Arboricultural Assessment - This should not be referred to as a specification of Arboricultural Works.
Tag No. Species
Ag
e
He
igh
t
He
igh
t to
c
an
op
y
No
rth
So
uth
Ea
st
Wes
t
Vit
ali
ty
Sa
fe L
ife
Ca
teg
ory
Ste
m D
ia
(mm
)
Observations Risk
offered by tree
Target Assessment
Management options Priority for
Action
Risk offered
following Works
T157 Common
Lime M 14 3 5.5 5.5 5.5 5.5 Fair 20+ C2 600
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T159 Common
Lime M 14 3 5.5 5.5 5.5 5.5 Fair 20+ C2 600
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Broken branches visible within the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T160 Common
Lime M 20 3 6 6 6 6 Fair 20+ C2 700
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
T161 Common
Lime M 14 3 5.5 5.5 5.5 5.5 Fair 20+ C2 600
Large deadwood can be seen in the outer canopy. Significant epicormic shoots are visible throughout the canopy. Canopy has been reduced (topped) & redeveloped.
Moderate
Canopy overhangs the highway and pedestrian
access.
Remove large deadwood only. Crown lift to 5.2m to enable vehicle access.
<1 year Low
APPENDICES Barnes & Associates
Page 28 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
APPENDIX C – SITE PLAN
Orientation ( Estimated)
NORTH
Symbol Guide High Target Area Moderate Target Area Extreme Risk Tree High Risk Tree Moderate Risk Tree Low Risk Tree
Title: Tree Location Plan
Drawing No: BA5446/A
Date: 25/05/16
Drawn By: IB
Sale: Not to Scale. General NOTE: Thi plan should be v iewed in
COLOUR a monochrome copy should not be
relied upon, the plan should be v iewed in
conjunction with the Tree Assessment BA5446,
Available from Barnes and Associates.
Please do not scale form this drawing. All
dimensions should be checked on site, any
errors or divergences should be brought to the
attention of Barnes and Associates.
Copyright of Barnes & Associates. All right
described in Chapter IV of the Copyright,
Design & Patents Act 1988 have been
generally asserted © 25/05/2016. Copyright of
this plan remains with Barnes Associates until all
fees are paid in full.
Base image courtesy of © Google and third
party suppliers and based upon the Image
dated 25/05/2016.
APPENDICES Barnes & Associates
Page 29 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
A P P E N D I X D – F U R T H E R A S S E S S M E N T S Detailed below are the further assessments that have been identified during the initial site appraisal, these include both more detailed assessments to confirm the actual level of risk of trees highlighted in the report as well as the regular and seasonal assessment associated with normal site management. Urgent Further Assessment:
T 1 1 8
I d e a l l y - U n d e r t a k e T o m o g r a p h y o f n o t e d f a u l t . a t 3 . 5 m
< 6 M o n t h s
T 1 1 9
I d e a l l y - U n d e r t a k e T o m o g r a p h y o f n o t e d f a u l t . a t 4 m
< 6 M o n t h s
None Urgent Further Assessments:
T r e e s A f f e c t e d b y I v y
A s s e s s t h e c o n d i t i o n o f t h e s t e m a f t e r r e m o v i n g i v y . O n c e I v y h a s b e e n
c o n t r o l l e d
W h o l e s i t e
R e a s s e s s p e r i o d i c a l l y a n d p a r t i c u l a r l y a f t e r h i g h w i n d s . A d v i s o r y
Ongoing Assessment
R i s k A s s e s s m e n t
A s s e s s t h e a r e a s p o p u l a t e d b y T r e e s a n d t h e r i s k o f f e r e d b y t h e m t o s t r u c t u r e s a n d
s i t e u s e r s .
U n d e r t a k e o n a n 1 8 o r 3 0 m o n t h c y c l e a l t e r n a t i n g a s s e s s m e n t s b e t w e e n p e r i o d s w h e n t h e
t r e e s a r e i n a n d o u t o f l e a f .
A r b o r i c u l t u r a l
M a n a g e m e n t
P l a n
A s s e s s t h e t r e e s i n d e t a i l a n d i d e n t i f y b r o a d m a n a g e m e n t p r i n c i p a l s i n r e l a t i o n t o
t h e m a n a g e m e n t o f t r e e s .
U n d e r t a k e o n a f i v e c y c l e .
APPENDICES Barnes & Associates
Page 30 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
D E T A I L S O F F U R T H E R A S S E S S M E N T M E T H O D S .
We hope this information will help you choose the most appropriate assessment to meet your needs. Please find below a brief outline of methods that provide additional information in relation to tree safety. If you have any particular requirements in relation to your site then please feel free to discuss them with us, as we should be able to tailor information to suit your particular needs. INCREMENT BORE - After screwing the tube into the tree, an extractor is used to remove the wood core. The thickness of sound wood can be measured accurately. Increment borers provide good information but create a significant hole (up to 1cm or so) that can breach a trees internal defence mechanism, we typically only use this where there is a significant safety concern or as a last resort. RESISTOGRAPH - This measures the drilling resistance of a needle drill. Data can be displayed as a paper trace (shown opposite) or as a digital output for a more detailed assessment of the internal condition of the tree. Again this method can breach a trees internal defence mechanism and as a result we only use this method where there is strong suspicion of decay or to confirm other test results.
THERMAL IMAGING CAMERA (TI) - Produce images upon the amount of infrared energy emitted, transmitted, and reflected by an object. A thermal imaging camera will show subtle temperature changes when the tissues of the wood or bark are altered or destroyed by physical actions or pathogens in addition to identifying areas of restricted vascular activity or destroyed tissues below the surface. CHLOROPHYLL FLUORESCENCE – By measuring the capacity of a plant to carry out photochemistry this can provide a measure of health and identify impacts from a range of issues including stresses caused by environmental conditions. It is used as a means of detecting physiological damage caused by biotic or abiotic stress factors. The very nature of the technique ensures early detection of stress that could lead to decline well before visible symptoms manifest.
STRESS WAVE TIMER - Stress wave techniques are the equivalent of a single shot Tomograph. The time taken for a sound wave to travel across a known distance give an insight into the deterioration in wood structure. Deterioration in tree stems increases the time taken for the signal as the sound wave needs to travel around faults of decay or holes between the two sensors. The reference velocity depends on tree species.
APPENDICES Barnes & Associates
Page 31 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
STABILITY MODELLING – Key dimensional information is used to compute various factors in relation to tree stability, enabling determination and comparative evaluation of:
Tree wind load and centre of gravity.
Safety improvement following crown reduction.
Stability reduction by decay.
Tipping-stability reduction by root decay and/or trenching.
Enable safety-balancing between the retained stem cross-section and wind-load experienced by the tree.
This allows the determination of strength loss due to structural defects in the cross sections of stems and branches and anchorage plate losses in relation to canopy size and expected wind-loads. In addition, the method enables evaluation of load reduction by crown reduction pruning to further achieve higher safety in damaged trees. The inputs are based on observations rather than diagnostic instruments but enable accurate (if not as precise) estimations of safety which are sufficient for many tree assessment purposes. However, the precision of the evaluation can be increased by putting in results from proper sonic tomography or resistance drilling with density-calibrated devices. SONIC TOMOGRAPHY (SOT) - A non-invasive tool for assessing decay in trees – shown to the right. It works on the principle that sound waves passing through decay move more slowly than sound waves traversing solid wood. The Picus sonic tomogram sends sound waves from a number of points around a tree trunk to the same number of receiving points, the relative speed of the sound can be calculated, and a two-dimensional image of the cross-section of the tree, ‘a tomogram’, can be generated. Using the differences in the transit times between each pair of sensors, the Picus analysis software constructs a two-dimensional picture (acoustic tomogram), which show zones of differing sound transmission properties within the stem. These results can be combined with other scans in a 3D representation to provide a better understanding of the internal condition of the stem.
ELECTRICAL RESISTANCE TOMOGRAPHY (ERT) – This method gathers chemical information about the wood such as water and/or ion concentration and physical properties that provides information about the internal condition of the stem. Low resistivity can identify increased moisture content, whereas hollowed structures cause increases in resistance. After collecting all the measurements, the information is displayed in the form of a coloured distribution plan for analysis as shown opposite. Again, these results can be combined with other scans in a 3D representation to provide a better understanding of the internal condition of the stem. SWAY MONITORING - Sensors attached to the base of the tree enable us to test the root anchorage & stem stability. When wind blows trees start to sway and this load is transmitted into the ground via the stem and rootplate - transferred to the root plate. We use sensors to record sway motion of trees in natural winds. The motion of the tree shows the real response of a tree to the natural conditions and enable identification of excessive movement and helps identify weak trees.
APPENDICES Barnes & Associates
Page 32 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
STATIC PULLING TEST - The tree-pulling test provides information about the breaking stability of the trunk and the stability of the roots. It is used to assess a tree’s stability with regard to stem fracture and uprooting precisely and non-invasively.
In a pulling test, a load (substituting for the wind) is exerted on a tree using a winch and a steel cable. The reaction of the stressed tree under this defined load is measured with high resolution devices (elastometer and inclinometer), and the data obtained are compared with those of sound trees. The major components to be considered in such calculations are the wind-load (the surface of the load-bearing structure, tree height, etc.) and the material properties of green wood.
Please see the table below, which provides a comparison of the methods used in advanced tree assessment and their suitability to assessing particular features and an indication of relative cost. If you have any particular requirements in relation to your site or require a combination of assessment of your trees please feel free to discuss them with us, as we should be able to tailor information to suit your particular needs and would be happy to provide a fixed price quote.
Comparison of methods in advanced tree assessment
Blue ● Good Yellow ● Fair Red ● Unfavourable
Adapted from Roloff (2016)
Tipping Safety
Fracture Safety
Tree Vitality
Damage to Tree
Cost per test
Increment Bore ● ● ● ● Low
Resistograph ● ● ● ●
Thermal Imaging Camera ● ● ● ●
Chlorophyll Fluorescence ● ● ● ●
Stress Wave Timer ● ● ● ●
Stability Modelling ● ● ● ●
Sonic Tomography ● ● ● ●
Electrical Resistance Tomography ● ● ● ●
Sway Monitoring ● ● ● ●
Static Pulling Test ● ● ● ● High
APPENDICES Barnes & Associates
Page 33 of 34 Preliminary Risk Assessment of Snape Lime Avenue. For Snape Mrs E Kirby Our Ref. BA5446 – Printed Date 25 May 2016
© Barnes & Associates 2016
A P P E N D I X E – T R E E S & R I S K Tree owners should take a balanced and proportionate approach to tree management It is recognised that trees are managed for a variety of reasons and therefore that the expectation of a “suitable and sufficient risk assessment” referred to by the HSE varies with context. In general, the risk from trees has certainly reached the situation where residual risks (those that remain after management for safety) are sufficiently low that investment in additional measures is likely to be disproportionate to any safety benefi t. As the HSE itself notes in Reducing risks, protecting people:
“Any informed discussion quickly raises ethical, social, economic and scientific considerations, for example: … how to achieve the necessary trade-offs between benefits to society and ensuring that individuals are adequately protected; the need to avoid the imposition of unnecessary restrictions on the freedom of the individual.”
Extremely low risk of harm HSE guidance for its inspectors and local authority enforcement officers on the standard of tree risk management and the DARM research commissioned by the NTSG on behalf of landowners confirm that the overall real risk of serious harm from trees in the UK is “extremely low”. Indeed, the levels of risk are so low that they are “comparable to those that people regard as insignificant or trivial in their daily lives”, near the bottom of the spectrum of what the HSE considers as an acceptable risk:
“Risks falling into this region are generally regarded as insignificant and adequately controlled. We, as regulators, would not usually require further action to reduce risks unless reasonably practicable measures are available. The levels of risk characterising this region are comparable to those that people regard as insignificant or trivial in their daily lives. They are typical of the risk from activities that are inherently not very hazardous or from hazardous activities that can be, and are, readily controlled to produce very low risks.”
Reasonable risk management generally aims to provide trees that can be regarded stable in a normal / foreseeable, regularly experienced storm event in relation to the situation / context of the tree. In this region, this is reasonable to assume a ‘Storm’ of force 10 using the Beaufort Scale (55 - 63 miles per hour) of wind speeds on land will occur annually. It should be realised that all trees do pose a risk; recent work in Germany has shown even sound trees that would typically be regarded as safe can fail during high winds through various factors relating to wood physiology, dynamics and the relationship between the root system and the supporting soils. It should be remembered that for any given tree regardless of its stability, there will always be a wind load that has the potential to break or uproot a tree regardless of its condition. Typically, trees have evolved to fail in part, i.e. twigs and branches are sacrificed / fail from a parent tree rather than the tree being lost entirely. Observations at various sites in this country have found that twigs and branches, can break from trees at wind speeds of as little as 31 miles per hour, the upper limit of a ‘strong breeze’ as detailed in Beaufort Scale 6 (25 - 31 miles per hour). This has led to a recommendation for certain sites with grounds open to the public, being closed when the wind speeds approaching 'Near Gale' or Force 7, as detailed by the Beaufort Scale (32-38 miles per hour). Such failures are difficult to predict with any great level of detail and a general position is best adopted. Typically, the level of risk offered by trees will be significantly greater as the force of the wind increases, the threat from aerial parts i .e. deadwood, tight unions and elongated branches may remain even following remedial works. Typically, branch failures are likely to be limited to small diameter branches and to periods of extreme weather, though as often seen in any natural model, exceptions to the rule can be expected. Therefore, in managing trees we are aiming to limit or reduce the risk to nearby features, unfortunately it is not possible to remove the risk offered by a tree entirely. As an arborist, I am a tree specialist and use my knowledge, education, training and experience to examine trees, to recommend measures to enhance their beauty and health, and attempt to reduce the risk of living near trees. As a client, you may choose to accept or disregard these recommendations, or seek additional advice. As an arborist, I cannot detect every condition that could possibly lead to a tree or limb failure. Trees are living organisms that may fail in many ways, some of which we do not fully understand. Conditions are often hidden within the tree and below the ground. As arborists, we cannot guarantee that a tree will be healthy or safe under all circumstances, or for a specified period, of time. Sometimes trees may appear "healthy," but may be structurally unsound. Likewise, remedial treatment, like any medicine, cannot be guaranteed. Treatment, pruning and removal of trees may involve considerations beyond the arboricultural perspective, such as property boundaries and ownership, disputes between neighbours, planning issues, sight lines, landlord-tenant matters etc. Arborists cannot take such issues into account unless complete and accurate information is given to them. Likewise, as an arborist, I cannot accept any responsibility for the authorization or non-authorization of any recommended treatment or remedial measure. Furthermore, certain trees are borderline cases as to whether they should remain or be removed. Also, co nditions change, and a tree may need further monitoring in the future to determine its health and structure.
Even healthy trees unaffected by defects can fail in extreme weather conditions. Trees can be managed, but they cannot be controlled, and to live near a tree is to accept some degree of risk.
Barne Barnes & Associates, Rivermead, Skelton Road, Langthorpe, North Yorkshire, YO51 9BZ
Telephone: 01423 322 371 Fax: 01423 322 371 Mobile: 07831 530 563
Em Email:[email protected]
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Tree Surveys & Condition Reports
Tree Health & Safety Reports
Tree Risk Assessments
Tree Population Site Inventories
Estate Tree Management
Woodland Management
Tree Work Specification & Tenders
Insurance & Mortgage Reports
Decay Detection & Mapping – Picus
Windload & Stability Assessments
Development Site Tree Reports to BS5837
Arboricultural Implication Assessments (AIA)
Arboricultural Method Statements (AMS)
Construction Exclusion Zone Management
Tree Protection Plan Design
Tree Valuation & Replacement Costing
TPO Objections & Appeals
Tree planting Schemes
Landscape visual impact assessment
Landscape architecture