I understand what you are trying to put across but risk in relation to trees IMO is too subjective to be given a quantifiable "threshold". Statistics unfortunately, within any walk of life, are still open to too much human interpretation. Now i'm not saying QTRA tries to "bend" those statistics, not at all, but it is interpretation of risk that is key here.
for example.... taking your example:biggrin:
I'm not trying to be awkward, i just try to look at things from all angles.
So, 4,441 (4500) cars use that road in a day, we can presume that its quite a busy commuting road, even at 30mph. (Without using the QTRA calculator, what is the rationale of the target value being 1/10?) Looking at your sentence in bold, i feel again IMO, that this is too subjective to be quantified
Has it been taken into consideration, time of day that the tree/tree part "might" fail? Cars will be less frequent at night, or even the day compared to rush hour times...
Has it been taken into account what cars travel on that road? Is it a wealthy affluent ares/poor less affluent area? More affluent areas may have bigger and better/safer cars. Bigger, newer cars "tend" to be safer and more responsive than older models (pure speculation mind, but very subjective:biggrin:)
What about the people? We all drive differently, we all respond differently! Who's to say your reaction might not be good enough to react in time to a falling branch/tree and that mine would be (or vice versa). Again, subjective.... one might say clutching at straws or being obstinate but i disagree:biggrin:
I tend to agree with you here on the PoF being subjective and it also being down to experience, but para-phrasing it 'professional judgement' sidesteps the core theme here, that trees and the potential "risk" they may (or may not cause) is a VERY subjective subject.
Even every self-optimised tree with good vitality is open to subjectiveness, OK fair enough the 1/1,000,000 threshold set by HSE and professional bods is now "set" as you state, the base point reference and there is nothing that can change that (is there?), does it take into account 'professional judgement'?
We, or at least all those trained with numerous and numerouser years experience, are still fallible, we all get things wrong from time to time, and therein lies objectivenesses problem. What about healthy trees that have signs and symptoms of reduced vitality and vigour mis-read and mis-quantified?
Also how can you quantify "how many times more likely is the tree to fail, than the 1/1,000,000 tree" without it being subjective?
Lastly, kind of off on a tangent but one i feel is quite pertinent. Veteran and Ancient trees are becoming less and less (yes the ATF is doing a good job of recording the ones we have left and trying to save them) so how would a tree of this category stand up in a case of QTRA assessment in regards to keeping the tree for its important ecosystem/s if it where in a place where it's PoF may be within Targets of RoH?
And please, don't apologies on the long post, l like it when people have put time, effort and thought into a post reply. We may not agree on all things but debate IS healthy:thumbup:
Robin