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  <channel>
    <title>Public Discussion</title>
    <link>http://www.qtra.co.uk/forum/list.php?2</link>
    <description><![CDATA[Discussion about Quantified Tree Risk Assessment.]]></description>
    <language>EN</language>
    <pubDate>Thu, 24 Nov 2011 08:58:41 +0000</pubDate>
    <lastBuildDate>Thu, 24 Nov 2011 08:58:41 +0000</lastBuildDate>
    <category>Public Discussion</category>
    <generator>Phorum 5.1.16a</generator>
    <ttl>600</ttl>
    <item>
      <title>Re: Harry Bowen and Others v The National Trust - Felbrigg Hall, UK</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,488,489#msg-489</link>
      <author>Joe Atkinson</author>
      <description><![CDATA[Thanks, David - some interesting reading there.

Quite brilliant work by the outstanding Dr Lonsdale: a great man.

Pleased to count myself as 1 in 634...!

What I can usefully pull from these docs is some clarified guidance to improve my Contract Spec for tree inspections. Good stuff.

Cheers]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,488,489#msg-489</guid>
      <pubDate>Thu, 24 Nov 2011 08:58:41 +0000</pubDate>
    </item>
    <item>
      <title>Harry Bowen and Others v The National Trust - Felbrigg Hall, UK</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,488,488#msg-488</link>
      <author>David Evans</author>
      <description><![CDATA[Hi

I'm posting this message on the UKTC, QTRA, and QTRA public discussion forums.

Files from the 'Felbrigg Hall' case are now available from the 'Case Law' page of the QTRA website, which can be accessed from either the 'User's Area' or 'Manager's Area'.

http://tinyurl.com/c7gevwg

For those of you who might be unaware.  This is a tragic case where, during a school outing in a woodland at a National Trust property (Felbrigg Hall) in the UK, one boy was killed and three other children were seriously injured when they were unfortunate enough to be beneath a large branch of a European Beech tree at the very time it failed.

The files consist of the following; which are listed in chronological order after the judgment.

1) The Judgment
2) The Particulars of Claim
3) The Defence
4) The Claimants' arboriculturist expert witness (Julian Forbes-Laird) report
5) Appendices to Julian Forbes-Laird's expert witness report
6) The Defendant's arboriculturist expert witness (Dr David Lonsdale) report
7) The arboriculturist experts' joint statement
8) Julian Forbes-Laird (Claimant's expert witness) - 'Supplementary Report on QTRA'
9) Dr David Lonsdale (Defendant's expert witness) - response to the 'Supplementary Report on QTRA'

QTRA licensees/forum members will no doubt be particularly interested in 8) and 9), and how David Lonsdale used QTRA and the Health and Safety Executive's (HSE) Tolerability of Risk framework in his expert report 6) when determining whether the risk posed by the tree was acceptable.

Cheers

David]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,488,488#msg-488</guid>
      <pubDate>Wed, 23 Nov 2011 12:47:16 +0000</pubDate>
    </item>
    <item>
      <title>Re: Hort Week: Barrell On...</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,485,487#msg-487</link>
      <author>Joe Atkinson</author>
      <description><![CDATA[Thanks, Mike

What surprises me, I think, is the reluctance to embrace the pluses of QTRA: hard - surely? - to make a case that a &quot;priestly caste&quot; is necessary to read the entrails and master the &quot;art&quot; of tree hazard management. Why not embrace the science?

What prompted me to post is that I have been mulling over a point made by a contributor on R4 last week (Food Show, I think) to a discussion about diet and, specifically, calorie counting. The point was (i'm paraphrasing) that, as ever, people argue about interpretations, but it is recognised in hindsight that talking in terms of calories framed the debate on a solid, statistical, scientific basis, taking the &quot;moralisers and the quacks&quot; out of the picture. That struck a bell with me, making me think of the huge disconnect between internal arb debate and the woeful ignorance of trees, tree risk and tree management I experience daily.

The more we prune trees, the more people will continue to expect it. Why are we pruning?

Keep up the good work!]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,485,487#msg-487</guid>
      <pubDate>Fri, 28 Oct 2011 14:34:12 +0000</pubDate>
    </item>
    <item>
      <title>Re: Hort Week: Barrell On...</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,485,486#msg-486</link>
      <author>admin</author>
      <description><![CDATA[Joe

I have pasted the clip below in quotes. The full article requires a subscription.

&quot;How we assess the risk from trees matters because the consequences of getting it wrong can be both spectacular and devastating when a tree fails. Traditionally, arborists used their eyes and experience to work out what to cut off and what to leave. In retrospect, this was quite a hit and miss approach. But it worked because the risk from trees was kept very low - a legacy that we still enjoy today.&quot;

Whether or not this is controversial, I'm not sure.  This seems to me to be what is referred to in the risk literature as managing 'secondary risk', where the expert focusses on the risk to themself and triggers what are referred to as 'unintended consequences' of risk assessment, where benefits are unecessarily lost to risk control measures.  

That experts prescribe risk averse control measures to be implemented within a specified timeframe is most probably why many large landowners do not seek the advice of tree experts. The financial cost associated with this 'risk table tennis can be just too much for the landowner, not just financially but in destruction of the tree asset.  

Is it really desirable to keep the risk from falling trees 'very low'?  I don’t think that it is and question the costs associated with this approach as did the Risk and Regulatory Advisory Council.  Even the Health and Safety Executive recognises that risk minimisation is inappropriate due to the loss of associated benefits and financial cost of implementing risk controls.

The risk tide is turning and our industry is at risk of being marginalised.

Mike Ellison]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,485,486#msg-486</guid>
      <pubDate>Fri, 28 Oct 2011 10:25:45 +0000</pubDate>
    </item>
    <item>
      <title>Hort Week: Barrell On...</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,485,485#msg-485</link>
      <author>Joe Atkinson</author>
      <description><![CDATA[Controversial stuff!

http://www.hortweek.com/news/login/1099549/

Current issue, I think?]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,485,485#msg-485</guid>
      <pubDate>Fri, 28 Oct 2011 07:47:49 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistics relating to the incidence of death or injuries arising from falling trees or limbs. Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,478#msg-478</link>
      <author>admin</author>
      <description><![CDATA[Hi Ross

In the UK, the Centre for Decision Analysis and Risk Management based at Middlesex University carried out some research on this and from the available records - average 6.4 deaths per year - concluded that the risk of death to the population from tree failure is around 1 in 10,000,000.  I recall that Mark Hartley, an arborist from Sydney, suggested that in Australia the death rate is somewhere in the region of 1.4 per annum wtih a population of around 20,000,000.  I will check this out with Mark and come back to you if it is substantially in error.

Regards
Mike Ellison]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,478#msg-478</guid>
      <pubDate>Thu, 22 Sep 2011 08:04:24 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistics relating to the incidence of death or injuries arising from falling trees or limbs. Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,477#msg-477</link>
      <author>Ross Clark</author>
      <description><![CDATA[Sorry, I filled in the wrong bit.

What I am looking for is info on statistics relating to the incidence of death or injury as the result of falling trees or limbs.

Thanks
Ross]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,477#msg-477</guid>
      <pubDate>Wed, 21 Sep 2011 23:52:46 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,468#msg-468</link>
      <author>admin</author>
      <description><![CDATA[If you put your name on your post, I will respond to your query.

Mike Ellison, forum administrator]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,468#msg-468</guid>
      <pubDate>Sat, 01 May 2010 12:03:31 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,467#msg-467</link>
      <author>treeman</author>
      <description><![CDATA[You don't seem to have received my last post in which I thanked Mark for his response, and added that what I was really after was some evidence, rather than just a statement of opininon.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,467#msg-467</guid>
      <pubDate>Fri, 30 Apr 2010 11:22:46 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,465#msg-465</link>
      <author>admin</author>
      <description><![CDATA[We have posted your query onto the User Discussion forum and Mark has responded to this. Perhaps others will also respond.

As administrator, I avoid getting too involved with questions from anonymous sources but would be happy to respond to an open enquiry.

Mike Ellison]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,465#msg-465</guid>
      <pubDate>Wed, 21 Apr 2010 16:55:01 +0000</pubDate>
    </item>
    <item>
      <title>Re: Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,464#msg-464</link>
      <author>Mark Hartley</author>
      <description><![CDATA[There are some good statistics available on tree related fatalities and on property damage from storms that support the fact that the QTRA process, when used by qualified practitioners, does not result in the underestimation of the Risk of Significant Harm.

In addition there is bountiful data and validity for key issues such as vehicle occupancy rates, hours in a day allometry etc

Lastly, QTRA is a robust and more importantly transparent system that follows standard risk assessment protocols.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,464#msg-464</guid>
      <pubDate>Tue, 20 Apr 2010 23:34:19 +0000</pubDate>
    </item>
    <item>
      <title>Statistical evidence for QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,463,463#msg-463</link>
      <author>treeman</author>
      <description><![CDATA[Does anyone have any statistical evidence that QTRA is a valid system?]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,463,463#msg-463</guid>
      <pubDate>Mon, 19 Apr 2010 14:21:46 +0000</pubDate>
    </item>
    <item>
      <title>Re: QTRA in court</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,452,454#msg-454</link>
      <author>sarah</author>
      <description><![CDATA[Thanks Andy, 
would there be transcripts of your hearings I could access, I am trying to build a system which will allow me to order works/removals on hazardous trees without having to obtain local government councillors approval, I am hoping QTRA will form part of this system.
I am happy for the moderator to pass on my email address if you would prefer not to post the information.

Sarah]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,452,454#msg-454</guid>
      <pubDate>Wed, 10 Jun 2009 03:12:14 +0000</pubDate>
    </item>
    <item>
      <title>Re: QTRA in court</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,452,453#msg-453</link>
      <author>Andy Smith</author>
      <description><![CDATA[I have used the system at a TPO appeal and in a planning hearing to demonstrate that I have taken into account the whole scenario and done so in a systematic way that can be broken down in understandable pieces

Andy]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,452,453#msg-453</guid>
      <pubDate>Tue, 09 Jun 2009 08:50:23 +0000</pubDate>
    </item>
    <item>
      <title>QTRA in court</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,452,452#msg-452</link>
      <author>sarah</author>
      <description><![CDATA[Hello, 
Can you please tell me if you know of any situation where QTRA has been used in a court or tribunal hearing. 
Thanks Sarah]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,452,452#msg-452</guid>
      <pubDate>Tue, 09 Jun 2009 00:02:32 +0000</pubDate>
    </item>
    <item>
      <title>Re: Accuacy of data</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,405,451#msg-451</link>
      <author>andy charlett</author>
      <description><![CDATA[Mike Ellison Wrote:
-------------------------------------------------------
&gt; Mark
&gt; 
&gt; My reply is interwoven with your posting.
&gt; 
&gt; Regards
&gt; 
&gt; Mike Ellison
&gt; 
&gt; --------------------------------------------------
&gt; ----
&gt; &gt; Whilst the system produces statistical data, I
&gt; &gt; have yet to see research data to support its
&gt; &gt; accuracy. Based on Australian figures, the risk
&gt; of
&gt; &gt; death or serious injury is extreemely low (less
&gt; &gt; than 1 in a 1,000,000 of population). Given
&gt; that
&gt; &gt; there are more than 10 trees for every person
&gt; the
&gt; &gt; odds of a tree causing problems is less than 1
&gt; in
&gt; &gt; 10,000,000. How then do we account for the
&gt; &gt; problems we do have? Clearly these are the
&gt; result
&gt; &gt; of trees that have a lot higher risk of failure
&gt; &gt; that are high trafic areas!
&gt; 
&gt; ME: The data are published as refered to below. 
&gt; Without going into the figures that you have
&gt; quoted, what you are discussing is risk of death
&gt; or serious harm (RoH) from tree failure in the
&gt; population as a whole, which is likely to be very
&gt; low (in the region of 1/5,000,000 in the UK  based
&gt; on historical data).  When we look at individual
&gt; land ownership, one land owner may have a RoH far
&gt; lower than 1/5,000,000 and anther land owner will
&gt; have a RoH that is much higher.  Whilst
&gt; 1/5,000,000 may be the mean, there are huge peaks
&gt; and troughs,  which accounts for the fact that
&gt; some tree owners have problems with high RoH
&gt; 
&gt; &gt; Given that it is these trees that are the
&gt; subject
&gt; &gt; of risk it would seem that the data on these
&gt; would
&gt; &gt; need to be extreemely accurate. The concern I
&gt; have
&gt; &gt; is that the assesment is subjective and not
&gt; &gt; quantataive at this point. Yes the tree does
&gt; have
&gt; &gt; girdling roots but can I say to what extent
&gt; that
&gt; &gt; this has impacted on the stability of the tree
&gt; and
&gt; &gt; the thigmomorphogenic responses. As a result we
&gt; &gt; generally err on the side of caution and assume
&gt; &gt; the risk is higher than it is. (Hence the
&gt; &gt; Wessolley Mattheck debate)
&gt; 
&gt; ME: The starting point is the question &quot;are there
&gt; any significant targets?&quot; because if there are
&gt; not, there cannot be a significant risk of
&gt; significant harm.  Targets can be accurately
&gt; quantified by frequency of occupation or by repair
&gt; or replacement value.  I believe that you are
&gt; correct in suggesting that as aresult of the
&gt; difficulty in interpreting the mechanical effects
&gt; of decay and defects, we err on the side of
&gt; caution.  If your assessment of probability of
&gt; failure (PoF) is cautious, this will be reflected
&gt; in the qtra RoH outcome. However, qtra has
&gt; substantially improved my assessment of PoF and
&gt; therefore improved the outcome of the qtra
&gt; assessments. And yes we can quantify and improve
&gt; the assumptions that we are already basing our
&gt; decisions upon.
&gt; &gt; 
&gt; 
&gt; &gt; Clearly any program that considers the size of
&gt; the
&gt; &gt; falling parts, the probable frequency and the
&gt; &gt; target must pick out the more hazardous trees
&gt; (eg
&gt; &gt; the ISA hazard assesment program) but how is
&gt; this
&gt; &gt; subjectivity converted into statistical
&gt; accuracy
&gt; &gt; without reseach data? 
&gt; 
&gt; We use our best estimates and as we use the qtra
&gt; procedures and observe trees that have been the
&gt; subject of our assesments, our assessments become
&gt; more accurate. Research data could improve our
&gt; understanding of tree failures as a proportion of
&gt; the opulation and this is something that I am
&gt; hoping to assist with by encouraging cooperation
&gt; with the ITFD and through other avenues.  Have you
&gt; had a look at the articles under the 'Resources
&gt; for Tree Managers' section of the qtra website?
&gt; 
&gt; 
&gt; &gt; If any arborist can tell me the liklihood of a
&gt; &gt; 100mm dead branch falling I would like to know
&gt; how
&gt; &gt; they do so. 
&gt; 
&gt; Based on species, size and condition, it is not
&gt; unreasonable to expect s skilled arborist to be
&gt; able to estimate how likely it is that the dead
&gt; branch will fail.  Currently, this skill requires
&gt; improvement and use of qtra can only help advance
&gt; our observational techniques.
&gt; 
&gt; 
&gt; Instead we assume that it can fall at
&gt; &gt; any time and it will most certainly fail so we
&gt; &gt; might as well be smart and remove or at least
&gt; &gt; reduce it if we want to keep the habitat. 
&gt; 
&gt; This approach would fail to take due consideration
&gt; of targets so I assume that this would be in the
&gt; context of the target.  In terms of safety, the
&gt; majority of dead branches are irrelvant because
&gt; either the target value is so low or the usage of
&gt; the site is substantially reduced during the
&gt; weather conditionsthat are most likely to result
&gt; in failure of the branch.  Judging by the
&gt; substantially degraded state of most fallen dead
&gt; branches, it is fairly safe to assume that they
&gt; degrade over a period of years and that the
&gt; failure of any particular branch in the coming
&gt; year is by no means certain.
&gt; 
&gt; 
&gt; On the
&gt; &gt; other hand what are the actual statistical
&gt; figures
&gt; &gt; on death or serious injury due to the failure of
&gt; a
&gt; &gt; dead branch of this size. Again here in
&gt; Austarlia
&gt; &gt; the odds are very very small.
&gt; 
&gt; To the best of my knowledge, there are none.
&gt; 
&gt;  
&gt; &gt; If 1 in 10,000 is an acceptable risk is there
&gt; data
&gt; &gt; for 10,000 trees at that risk level to prove or
&gt; &gt; falcify the statistical assertion. Throwing the
&gt; &gt; average tree with a risk factor of less than 1
&gt; in
&gt; &gt; 10,000,000 into the data soop is surely poor
&gt; &gt; ststistics
&gt; 
&gt; You may have misunderstood our use of the 1/10,000
&gt; risk of significant harm as a threshhold of
&gt; acceptable risk.  Other sources suggest that
&gt; people generally would not spend their own
&gt; resources to reduce an annual risk of death that
&gt; was already as low as 1/10,000 and that a 1/10,000
&gt; risk of death is broadly acceptable where the risk
&gt; is imposed on the public in the wider interest.  I
&gt; am uncear as to how data for 10.000 trees would
&gt; prove or falsify this advised limit (which is not
&gt; a not statistical assertion).  Where does your
&gt; second point relate to qtra?
&gt; &gt; 
&gt; &gt; In short what is the error factor and does the
&gt; &gt; data consider the mean, mode, maximum, minimum
&gt; or
&gt; &gt; average liklihood of any event. What is the
&gt; &gt; statistical difference between the minimum and
&gt; &gt; maximum (the error factor) and how have these
&gt; &gt; figures been proved? I certainly would hate to
&gt; &gt; find myself in a court case because I acted too
&gt; &gt; quickly or because I did not act quickly
&gt; enough.
&gt; 
&gt; The issue of error is currently being considered,
&gt; but we do not operate to an absolute prescriptive
&gt; threshold and any outcome that contradicts
&gt; intuition can be reassessed and refined if
&gt; necessary.  The system calculates the likelihood
&gt; that a significant loss will occur as a result of
&gt; tree failure. The data used are set out in the
&gt; articles mentioned above and there have been
&gt; various modifications to the process since their
&gt; publication.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,405,451#msg-451</guid>
      <pubDate>Fri, 17 Apr 2009 01:34:34 +0000</pubDate>
    </item>
    <item>
      <title>Re: Accuacy of data</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,405,449#msg-449</link>
      <author>admin</author>
      <description><![CDATA[PDB

Because I do not wish to present a wholly biased view, I posted your message on the User Discussion List where one of our Australian users responded and agreed that I could transfr his response here.
-------------------------------------------------------
Sorry,
 
What a load of crock! QTRA is not about predicting the future and all models rely on past data since it is impossible to this stage to look at future data. 
 
To suggest that climate change may potentially cause significant changes would certainly be true if the change were rapid but the evidence is that the change in the next 12 months will be gradual and based on figures for the last decade the temperature will continue to fall by 0.05 degrees each year (Global cooling?). Not sure how that will affect anything! 
 
The assertion &quot;just because we don't expect something to happen doesn't mean there isn't a 50% chance that it will&quot; is ludicrous! QTRA is not about expectations it is about probability and if the chance of it happening is 50% then the odds are 1 in 2. My city has not been subject to a 1 in 100 flood event for over 120 years. What is the odds of getting a 1 in 100 flood in the next year? That's right 1 in 100 yet our expectations are that we haven't had one for ages so one is due soon! And if we get one next year the odds of having one the year after is 1 in 100. We certainly wouldn't expect to get two floods in a row but expectations do not alter probability. Probability, if we were entirely objective, should alter our expectation.
 
As far as freak storms are concerned I think there are really good models available and Sydney and other capital cities around the world have been and will be hit by freak storms. Correct me if I am wrong but we are not trying to consider &quot;all acts of God&quot;. 
 
When a 1 in 100 wind storm hits trees are going to be damaged. When a 1 in 1000 wind storm hits lots of trees are going to be damaged but to be honest trees are still one of our lowest risks at these times. For those who may not have considered it a tornado represents pretty esteemed winds, they kill people and whilst trees debris may be some of the debris that gets thrown around so do cars, roofs and even whole buildings. I still take my odds with trees and a reasonable defence that acts of God will still deemed as acts of God.
 
Mark
----- Original Message ----- 
From: Mike Ellison 
To: qtra-users@lists.qtra.co.uk 
Sent: Thursday, November 06, 2008 8:30 PM
Subject: [qtra-users] Message on QTRA public discussion forum


The following message has been posted on the QTRA Public Discussion Forum.  I'm posting it here to make QTRA Users aware of the Public Forum and also I wonder whether anyone might be interested in replying to postings.  The forum has been heavily bombarded with spam and for this reason every post needs to be moderated by me, which in turn sometimes slows down the time that it takes for a message to appear on the webpage.
 
Mike Ellison
 
 
Re: Accuacy of data
Posted by: PDB (89.145.205.172)
Date: Thursday, 06-Nov-2008, 08:30:20


Through my own experience of dealing with hazard trees over twenty years, it is my carefully considered opinion that QTRA is misleading in its use of the term 'Quanitified'; quantified risk assessment in other fields is based on complex statistical modelling. In comparison, the data we have on probability of failure is very poor. There are powerful factors that remain outside of predictability e.g. the weather and risk of hidden factors would also need quantifying. 

In this respect, QTRA is a 'qualitative' assessment, based on broad objective criteria that can be applied to ascertain priority based on reasonable practicability. 

The risk is that applying a statistical approach can lure the duty holder into a sense of security. If they percieve the risk to be low, routine tree managment can be neglected. This could offset risks to a later stage at a higher level with reduced options - neglected trees are difficult to safely retain and manage. The scurrent statistics of death may be nothing more than the result of twenty years routine tree maintenance to BS3998:1989. 

The world financial crisis is a rude remider of how quantified risk assessment in the banking system failed to assess the net effect of various risks compounding one another to create serius consequences, and failure to act cautiously with such risks because they were perceived to be too remote. 

There are parallels with tree risk assessment; just because we don't expect something to happen doesn't mean there isn't a 50% chance that it will. That point needs to be stressed to the duty holder for them to decide if they are prepared for the possible consequences. I feel the name and use of odds of QTRA system doesn't explain the brevity of this issue. 

Use of statistics to draw odds, is a little like driving down the motorway looking in the rear view mirror. Climate change and the weather are big variable factors on tree risk assessment (always assuming a target), and that requires caution. 

Regards 
PDB


--------------------------------------------------------------------------------]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,405,449#msg-449</guid>
      <pubDate>Sat, 06 Dec 2008 09:48:42 +0000</pubDate>
    </item>
    <item>
      <title>Re: Accuacy of data</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,405,446#msg-446</link>
      <author>PDB</author>
      <description><![CDATA[Through my own experience of dealing with hazard trees over twenty years, it is my carefully considered opinion that QTRA is misleading in its use of the term 'Quanitified'; quantified risk assessment in other fields is based on complex statistical modelling. In comparison, the data we have on probability of failure is very poor. There are powerful factors that remain outside of predictability e.g. the weather and risk of hidden factors would also need quantifying.

In this respect, QTRA is a 'qualitative' assessment, based on broad objective criteria that can be applied to ascertain priority based on reasonable practicability.

The risk is that applying a statistical approach can lure the duty holder into a sense of security. If they percieve the risk to be low, routine tree managment can be neglected. This could offset risks to a later stage at a higher level with reduced options - neglected trees are difficult to safely retain and manage. The scurrent statistics of death may be nothing more than the result of twenty years routine tree maintenance to BS3998:1989. 

The world financial crisis is a rude remider of how quantified risk assessment in the banking system failed to assess the net effect of various risks compounding one another to create serius consequences, and failure to act cautiously with such risks because they were perceived to be too remote.

There are parallels with tree risk assessment; just because we don't expect something to happen doesn't mean there isn't a 50% chance that it will. That point needs to be stressed to the duty holder for them to decide if they are prepared for the possible consequences. I feel the name and use of odds of QTRA system doesn't explain the brevity of this issue. 

Use of statistics to draw odds, is a little like driving down the motorway looking in the rear view mirror. Climate change and the weather are big variable factors on tree risk assessment (always assuming a target), and that requires caution.

Regards
PDB]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,405,446#msg-446</guid>
      <pubDate>Thu, 06 Nov 2008 08:30:20 +0000</pubDate>
    </item>
    <item>
      <title>Re: Welcome to QTRA Public Discussion Forum</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,1,439#msg-439</link>
      <author>maggie kinnes</author>
      <description><![CDATA[I love trees and I do not like seeing them chopped down/removed but I am in favour of people planting and maintaining trees responsibly and many people are just not doing so. It goes far beyond trees that might be diseased. Many trees are allowed to grow far too tall/wide for the area they are planted ( eg domestic garden). Legislation was put in place for lleylandi but deciduous trees spread roots much further and do more damage to  foundations of buildings. They are also more likely to cause damage to other people's gardens (eg damage to lawns they overhang through shade and dropping leaves) as well as having more likelyhood of coming down in string wind or even a large branch falling.

 Tree owners may owe a duty of care but it is extremely time consuming and and expensive to take action (generally court is the only right of recourse) against people who are irresponsible and will not take time and investment to look after plants in their gardens which are causing misery and damage to surrounding property as well as posing a significant health and safety risk. The same rules that apply to lleylandi should apply to deciduous trees. If trees are diseased, causing unnecessary damage to neighbouring property or presenting a significant risk to safety if they were to fall (or even a large branch to become detached) the person on whose property they are growing should be required to take action to  have then removed or proper tree surgery carried out. If not they should be panalised to the amount it would cost to have the relevant tree surgery performed. Affected people should be able to report trees they think should come into this category. This will impact on household insurance costs  but people have to take responsibility for their property and what they grow on it.

I support this move but wish it were widened to cover not just inspections for trees with disease but also any trees that are potentially danagerous due to size etc and also causing damage to neighbouring property.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,1,439#msg-439</guid>
      <pubDate>Fri, 20 Jun 2008 19:52:56 +0000</pubDate>
    </item>
    <item>
      <title>Re: Is this suitable for me?</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,437,438#msg-438</link>
      <author>admin</author>
      <description><![CDATA[Hi Jamie

This probably isn't the best place to as the question as its really a place for tree managers to post their queries about the Quantified Tree Risk Assessment method and almost all messages are answered by me and my other role is delivering the training.

We run two training workshops both of which run for one day.  The first is the Quantified Tree Risk Assessment user training, which involves entering into a licence agreement and paying an annual fee.  This is a methodology for people who are regularly assessing the risks from tree failure.  From what you've said, I dont think that this is going to be of particular benefit to you.

The second workshop is the Practitioners Guide to Visual Tree Assessment and it sounds as though you would probably gain a great deal from this.  The workshop looks at some basic tree anatomy and tree biology with instruction on the interpretation of growth patterns in relation to defects, decay and mechanical stability of trees.  We also look at the relationships between fungi and trees.

To get a independant view, you could post your question on the UKTC Tree Care forum where you will almost certainly get a response.  http://www.tree-care.info/uktc

Regards

Mike Ellison]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,437,438#msg-438</guid>
      <pubDate>Thu, 08 May 2008 19:59:06 +0000</pubDate>
    </item>
    <item>
      <title>Is this suitable for me?</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,437,437#msg-437</link>
      <author>Jamie Gill</author>
      <description><![CDATA[I help my father run a succesful tree surgery company in West Yorkshire. I had a meeting with the local council yesterday and he said this would be a good course to take, as not many people have it and the views this course opens is inevitable. I've been in the industry 6 years now, and with this been a day course it would be ideal. As I have hands on knowledge, I dont want to take the course if it isnt going to make sense. I have done a day in basic tree surgery, but as I can only get day courses in at the moment I am quite limited. Just your opinion would be greatly appreciated.

Kind Regards
Jamie Gill]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,437,437#msg-437</guid>
      <pubDate>Thu, 08 May 2008 18:23:52 +0000</pubDate>
    </item>
    <item>
      <title>Re: Some questions cioncerning QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,6,431#msg-431</link>
      <author>admin</author>
      <description><![CDATA[Phil

I apologise, but I deleted your post to the forum while I was deleting spam.  I have copied the text below.

Absolutely no worries when it comes to asking questions and expressing concerns, taht's what the forum is here for.  Unfortunately it doesn't get a great deal of use.

I hope that my replies were of some help.  I look forward to you doing the training and feel sure that you will find it worthwhile.

Regards

Mike Ellison

-----------------------------------------------------------------------

Mike,

I have only just seen this thread now, and knowing more now than I did back then, I can only apologise for using the term 'wishy-washy' to describe QTRA. 

I am interested in attending a training course. Probably the one in March at Exeter Uni. 

See you then.

Phil]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,6,431#msg-431</guid>
      <pubDate>Sat, 29 Sep 2007 14:47:13 +0000</pubDate>
    </item>
    <item>
      <title>Re: Accuacy of data</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,405,406#msg-406</link>
      <author>Mike Ellison</author>
      <description><![CDATA[Mark

My reply is interwoven with your posting.

Regards

Mike Ellison

------------------------------------------------------
&gt; Whilst the system produces statistical data, I
&gt; have yet to see research data to support its
&gt; accuracy. Based on Australian figures, the risk of
&gt; death or serious injury is extreemely low (less
&gt; than 1 in a 1,000,000 of population). Given that
&gt; there are more than 10 trees for every person the
&gt; odds of a tree causing problems is less than 1 in
&gt; 10,000,000. How then do we account for the
&gt; problems we do have? Clearly these are the result
&gt; of trees that have a lot higher risk of failure
&gt; that are high trafic areas!

ME: The data are published as refered to below.  Without going into the figures that you have quoted, what you are discussing is risk of death or serious harm (RoH) from tree failure in the population as a whole, which is likely to be very low (in the region of 1/5,000,000 in the UK  based on historical data).  When we look at individual land ownership, one land owner may have a RoH far lower than 1/5,000,000 and anther land owner will have a RoH that is much higher.  Whilst 1/5,000,000 may be the mean, there are huge peaks and troughs,  which accounts for the fact that some tree owners have problems with high RoH

&gt; Given that it is these trees that are the subject
&gt; of risk it would seem that the data on these would
&gt; need to be extreemely accurate. The concern I have
&gt; is that the assesment is subjective and not
&gt; quantataive at this point. Yes the tree does have
&gt; girdling roots but can I say to what extent that
&gt; this has impacted on the stability of the tree and
&gt; the thigmomorphogenic responses. As a result we
&gt; generally err on the side of caution and assume
&gt; the risk is higher than it is. (Hence the
&gt; Wessolley Mattheck debate)

ME: The starting point is the question &quot;are there any significant targets?&quot; because if there are not, there cannot be a significant risk of significant harm.  Targets can be accurately quantified by frequency of occupation or by repair or replacement value.  I believe that you are correct in suggesting that as aresult of the difficulty in interpreting the mechanical effects of decay and defects, we err on the side of caution.  If your assessment of probability of failure (PoF) is cautious, this will be reflected in the qtra RoH outcome. However, qtra has substantially improved my assessment of PoF and therefore improved the outcome of the qtra assessments. And yes we can quantify and improve the assumptions that we are already basing our decisions upon.
&gt; 

&gt; Clearly any program that considers the size of the
&gt; falling parts, the probable frequency and the
&gt; target must pick out the more hazardous trees (eg
&gt; the ISA hazard assesment program) but how is this
&gt; subjectivity converted into statistical accuracy
&gt; without reseach data? 

We use our best estimates and as we use the qtra procedures and observe trees that have been the subject of our assesments, our assessments become more accurate. Research data could improve our understanding of tree failures as a proportion of the opulation and this is something that I am hoping to assist with by encouraging cooperation with the ITFD and through other avenues.  Have you had a look at the articles under the 'Resources for Tree Managers' section of the qtra website?


&gt; If any arborist can tell me the liklihood of a
&gt; 100mm dead branch falling I would like to know how
&gt; they do so. 

Based on species, size and condition, it is not unreasonable to expect s skilled arborist to be able to estimate how likely it is that the dead branch will fail.  Currently, this skill requires improvement and use of qtra can only help advance our observational techniques.


Instead we assume that it can fall at
&gt; any time and it will most certainly fail so we
&gt; might as well be smart and remove or at least
&gt; reduce it if we want to keep the habitat. 

This approach would fail to take due consideration of targets so I assume that this would be in the context of the target.  In terms of safety, the majority of dead branches are irrelvant because either the target value is so low or the usage of the site is substantially reduced during the weather conditionsthat are most likely to result in failure of the branch.  Judging by the substantially degraded state of most fallen dead branches, it is fairly safe to assume that they degrade over a period of years and that the failure of any particular branch in the coming year is by no means certain.


On the
&gt; other hand what are the actual statistical figures
&gt; on death or serious injury due to the failure of a
&gt; dead branch of this size. Again here in Austarlia
&gt; the odds are very very small.

To the best of my knowledge, there are none.

 
&gt; If 1 in 10,000 is an acceptable risk is there data
&gt; for 10,000 trees at that risk level to prove or
&gt; falcify the statistical assertion. Throwing the
&gt; average tree with a risk factor of less than 1 in
&gt; 10,000,000 into the data soop is surely poor
&gt; ststistics

You may have misunderstood our use of the 1/10,000 risk of significant harm as a threshhold of acceptable risk.  Other sources suggest that people generally would not spend their own resources to reduce an annual risk of death that was already as low as 1/10,000 and that a 1/10,000 risk of death is broadly acceptable where the risk is imposed on the public in the wider interest.  I am uncear as to how data for 10.000 trees would prove or falsify this advised limit (which is not a not statistical assertion).  Where does your second point relate to qtra?
&gt; 
&gt; In short what is the error factor and does the
&gt; data consider the mean, mode, maximum, minimum or
&gt; average liklihood of any event. What is the
&gt; statistical difference between the minimum and
&gt; maximum (the error factor) and how have these
&gt; figures been proved? I certainly would hate to
&gt; find myself in a court case because I acted too
&gt; quickly or because I did not act quickly enough.

The issue of error is currently being considered, but we do not operate to an absolute prescriptive threshold and any outcome that contradicts intuition can be reassessed and refined if necessary.  The system calculates the likelihood that a significant loss will occur as a result of tree failure. The data used are set out in the articles mentioned above and there have been various modifications to the process since their publication.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,405,406#msg-406</guid>
      <pubDate>Sat, 07 Oct 2006 12:39:24 +0000</pubDate>
    </item>
    <item>
      <title>Accuacy of data</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,405,405#msg-405</link>
      <author>Mark</author>
      <description><![CDATA[Whilst the system produces statistical data, I have yet to see research data to support its accuracy. Based on Australian figures, the risk of death or serious injury is extreemely low (less than 1 in a 1,000,000 of population). Given that there are more than 10 trees for every person the odds of a tree causing problems is less than 1 in 10,000,000. How then do we account for the problems we do have? Clearly these are the result of trees that have a lot higher risk of failure that are high trafic areas!

Given that it is these trees that are the subject of risk it would seem that the data on these would need to be extreemely accurate. The concern I have is that the assesment is subjective and not quantataive at this point. Yes the tree does have girdling roots but can I say to what extent that this has impacted on the stability of the tree and the thigmomorphogenic responses. As a result we generally err on the side of caution and assume the risk is higher than it is. (Hence the Wessolley Mattheck debate)

Clearly any program that considers the size of the falling parts, the probable frequency and the target must pick out the more hazardous trees (eg the ISA hazard assesment program) but how is this subjectivity converted into statistical accuracy without reseach data? 

If any arborist can tell me the liklihood of a 100mm dead branch falling I would like to know how they do so. Instead we assume that it can fall at any time and it will most certainly fail so we might as well be smart and remove or at least reduce it if we want to keep the habitat. On the other hand what are the actual statistical figures on death or serious injury due to the failure of a dead branch of this size. Again here in Austarlia the odds are very very small.

If 1 in 10,000 is an acceptable risk is there data for 10,000 trees at that risk level to prove or falcify the statistical assertion. Throwing the average tree with a risk factor of less than 1 in 10,000,000 into the data soop is surely poor ststistics.

In short what is the error factor and does the data consider the mean, mode, maximum, minimum or average liklihood of any event. What is the statistical difference between the minimum and maximum (the error factor) and how have these figures been proved? I certainly would hate to find myself in a court case because I acted too quickly or because I did not act quickly enough.

Mark]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,405,405#msg-405</guid>
      <pubDate>Sat, 07 Oct 2006 02:14:44 +0000</pubDate>
    </item>
    <item>
      <title>Re: Some questions cioncerning QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,6,7#msg-7</link>
      <author>admin</author>
      <description><![CDATA[Phil

Use of the qtra method is becoming increasingly accepted by the arboricultural industry and by tree managers.  VTA is not a risk assessment method.  VTA is about assessing the mechanical integrity of trees but does not consider the potential for harm or indeed the magnitude of harm that may arise from tree failure.

With regard to your second question, qtra is certainly not wishy-washy.  Qtra enables the person assessing the risks from tree failure to provide a probabilistic estimate of harm from tree failure and the person charged with managing the tree/s can make a well informed judgement based on this information. 

I suggest that you might get a view from the wider arboricultural community by posting your questions on the UK Tree Care Mailing List at http://lists.tree-care.info/uktc/.

Mike
]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,6,7#msg-7</guid>
      <pubDate>Sun, 28 May 2006 13:36:44 +0000</pubDate>
    </item>
    <item>
      <title>Some questions cioncerning QTRA</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,6,6#msg-6</link>
      <author>Phil Dye</author>
      <description><![CDATA[I am not a user (licensed or otherwise) of QTRA as yet as I have only just been made aware of it. I was wondering if anyone could answer a couple of questions I have of it.

1. I have read that it adheres to industry best practice in tree surveying. Is it widely used and does it hold much credibility when measuring up to other methods such as VTA and others.

2. By not actually having to state the safety of the tree and therefore not needing to recommend tree works to be carried out, it sounds like this may be a rather wishy-washy method of risk assessment taking the heat off the surveyor but at the cost of watering down the report. Please correct me if I am wrong because I have a genuine interest in QTRA.

I look forward to any replies.

Regards.

Phil]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,6,6#msg-6</guid>
      <pubDate>Sat, 27 May 2006 11:51:55 +0000</pubDate>
    </item>
    <item>
      <title>QTRA for non-arborist</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,2,2#msg-2</link>
      <author>Bryn Andrews</author>
      <description><![CDATA[
For the sake of discussion I suggest that

As assessing the probability of failure requires expert analysis I suggest that encouraging anybody buy a professionally qualified arborist to use the system could be detrimental to the whole QTRA systems standing?

Bryn]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,2,2#msg-2</guid>
      <pubDate>Fri, 21 Oct 2005 15:55:28 +0000</pubDate>
    </item>
    <item>
      <title>Welcome to QTRA Public Discussion Forum</title>
      <link>http://www.qtra.co.uk/forum/read.php?2,1,1#msg-1</link>
      <author>Mike Ellison</author>
      <description><![CDATA[The QTRA Public Discussion Forum is provided to encourage questions and discussion on the topic of tree safety and tree-failure risk assessment.

QTRA Licensed Users have access to the QTRA Discussion Mailing List but it is hoped that they will contribute their expertise and experieces to this Forum also.

Please feel free to post and answer questions and enter into discussions but please try to keep your posts on the topic of tree safety.


Mike Ellison
Quantified Tree Risk Assessment Ltd.]]></description>
      <category>Public Discussion</category>
      <guid isPermaLink="true">http://www.qtra.co.uk/forum/read.php?2,1,1#msg-1</guid>
      <pubDate>Sat, 17 Sep 2005 08:12:11 +0000</pubDate>
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