UKTC Archive

<<Can you please summarise what the difference between your proposed approach 
and QTRA would be?>>

Hi Julian

In short, one of VALID's aims is to simplify 'balancing tree risks and 
benefits' so the owner/manager and assessor can easily understand the issue 
when they need to.  And also be consistent in its application.  It turns out 
that because of the way that the engine of VALID has been put together, for 
the most part this is refreshingly straight forward.  Much of the 
decision-making is built into the App and you're walked through it.

As for the differences.  Well, it's now been over a year since I abandoned 
working with QTRA and made my bid for freedom, and it's been quite an 
eye-opening journey.  Off the top of my head, and assuming things haven't 
changed much, I guess the main differences are;

The risk-benefit policy (the new Creative Commons version is attached) leads 
with the benefits in a position statement as to why Tolerable AND ALARP 
(amber) and Acceptable (green) risks can reasonably be imposed.

There's no ALARP decisions between the 1/1000 - 1/10 000 level of risk.  No 
matter what the benefits are.

And whether benefits are accruing or depreciating has simplified the ALARP 
decision-making in the VALID Amber risk zone by linking it to which 
likelihood of failure benchmark colour the tree part is heading to.  However, 
there are few times that this decision has to be made.

I've made a really concerted effort to simplify the whole ALARP cost-benefit 
side of things - eg some VALID outputs will be "Amber | Tolerable AND ALARP" 
- because I think very few assessors are comfortable trying to work out 
whether risk reduction is 'proportionate' or 'grossly disproportionate', even 
after training and with guides.  I think less are actually trying to get 
their heads around it because it's difficult.  Most clients are simply 
confused by it.  And many assessors and owner/managers are simply treating a 
'Tolerable if ALARP' risk as though it were a 'Broadly Acceptable' risk.  
There's quite a few policy/strategies/plans out there that do this.

<<Also at p4 "To justify the additional costs of a Level 3 – Advanced 
assessment, the tree must have enough value and potential because of the 
benefits it provides." Does VALID have any means of evaluating value, 
potential and benefits in mind?>>

P.4?  There's only 3 pages.  No, it'll be a call on the part of the tree 
manager/owner because there's too many variables.  For example, the value of 
the tree might be low, say with CAVAT, but a petition of 5000 comes in from 
people who love the tree, and then a velociraptor is found nesting in it.  
Then there's the issue of costs of an Advanced assessment.  It's popped up on 
here a number of times, but a Beech tree with high amenity value is often 
felled if it is colonised by Meripilus giganteus no matter the level of risk 
or benefits.  Hopefully the Beech + Meripilus = Fell equation has been 
debunked, but this now seems to have moved onto the cost of a Static Load 
Test being too much to spend.  I think you can make a good qualitative 
judgement about likelihood of failure using the VALID likelihood of failure 
mnemonic, based on Paul Muir's invaluable experience of Static Load Tests in 
these circumstances, but that's probably for another thread.

<<As a related afterthought, in cases where an Advanced assessment is not 
required (perhaps because likelihood of failure is known with sufficient 
confidence) will there be no equivalent evaluation of value, potential and 
benfits before deciding on risk reduction work on proportionality grounds 
alone?>>

I'm not sure what you mean by risk reduction works on proportionality grounds 
alone?  If the risk is Amber - Tolerable AND ALARP, risk reduction work could 
still be carried out to reduce the risk to  Green - Acceptable if there's the 
budget and that's what the tree owner would like to do.  Given that most of 
VALID's amber risks require the likelihood of failure to be benchmarked from 
red, some tree work might well be wise to reduce the risk even when the risk 
is Tolerable AND ALARP to lessen the likelihood of losing the benefits 
because of the tree part failing.

Cheers

Acer ventura



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VALID - Tree Risk-Benefit Policy 12.17 CC.pdf
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