Tree Risk News

Just caught up with this week's Risk Business podcast, hosted by Maria Konnikova and Nate Silver.

At 24mins there's an insightful discussion about what words like Probable, Possible, and Likely mean.

Adam Kucharski's excellent short article, Possibly a Serious Possibility, sparked the conversation.

In the article, Kucharski explores the work of Sherman Kent. Kent is a legendary CIA Analyst who first highlighted the fundamental flaw of using vague language when expressing your uncertainty in a risk forecast.

Kent famously called these evasive terms, 'Lurking Weasels'.

Lurking weasels are words or phrases that are used to sound definitive and authoritative. But when you look at them closely, they're ways of avoiding decisions and dodging responsibility.

"What we consciously or subconsciously seek is an expression which conveys a definite meaning but at the same time either absolves us completely of the responsibility or makes the estimate at enough removes from ourselves as not to implicate us."
Sherman Kent

The world of tree risk management and assessment is littered with lurking weasels - or what we call Bafflegab.                   .

What Philip Tetlock (The Superforecasters guy) calls 'the illusion of communication'. Or 'vague verbiage'.

A recent standout lurking weasel in our Tree Risk Bafflegab Charts is the National Tree Safety Group's 'Low Occupancy', in Common Sense Risk Management of Trees (2nd Ed).

More about that lurking weasel in the next post.

In the meantime - what tree risk lurking weasels have you come across?

The opening of the Policy all in our Tree Risk-Benefit Management Strategies explains...

Trees give us many benefits that we need

Our Government Strategy templates have an Introduction section for the public.

In the introduction, we have a link to Halifax Regional Municipality's marvellous short 5m video. Trees of All Trades.

Tree of All Trades is an entertaining and engaging video about the benefits of urban trees.

We've not seen it bettered.

What is a Basic Tree Risk Assessment?

This question came up at the ISA Conference in Atlanta.

A Basic Tree Risk-Benefit Assessment with VALID is a very different animal to the ISA's Basic Tree Risk Assessment with TRAQ.

This is why...

VALID
You carry out all your risk assessments under the protective umbrella of a Tree Risk-Benefit Management Strategy.

We have 2 types of Tree Risk-Benefit Assessment, highlighted in our Strategy.

Passive Assessment
Is simply picking up on Obvious Tree Risk Features you can't help but notice, as you go about your day-to-day routine.

Anyone can carry out Passive Assessment.

Passive Assessment is a Duty Holder's most valuable tree risk asset.

That's because it's this high volume, low effort, day in day out  citizen science risk assessment that's most likely to pick up a red risk tree - well before an Arborist finds it with Active Assessment.

Active Assessment
Is looking for risks that might not be Acceptable or Tolerable.

It has 3 levels to it that increase in depth of evaluation.

Basic > Detailed > Advanced

We don't give these levels of assessment numbers because it adds nothing useful to their meaning.

Basic Validators (non-Arborists trained to recognise Obvious Tree Risk Features), and Validators carry out Basic Assessments.

Only Validators can carry out Detailed and Advanced Assessments. This is where they use our Tree Risk App, or other Safety Factor software, to work out whether the risk is Acceptable, Tolerable, Not Tolerable, or Not Acceptable. Up to these levels the Strategy is doing the assessment. The risk is Acceptable, unless there's obvious emergency work.

TRAQ
Has 3 levels of Assessment

Level 1 Limited Visual
Level 2 Basic
Level 3 Advanced

When putting VALID together, we wanted to align the levels of Active Assessment with TRAQ, for obvious reasons.

But, with the best will in the world, we could see nothing Basic about the TRAQ Basic Tree Risk Form.

In short...

A VALID Detailed Assessment is roughly the same level as a TRAQ Basic Assessment.

In the UK, Durham County Council (DCC) is the latest major duty holder to adopt a VALID approach to managing and assessing tree risk.

Here's DCC's Tree Management Policy.

DCC have integrated VALID's Government Tree Risk-Benefit Management Strategy model template into their policy.

All DCC's risk-benefit assessments are made under the protective umbrella of their Policy. Here's how they've zoned their occupancy, and go about their assessments in their Tree Inspection Procedure.

DCC's greatest tree risk asset is their policy and procedure.

After policy and procedure, DCC's most valuable risk asset isn't their 4 Validators (trained Arborists). It's the nearly 60 Basic Validators we've trained over the last week.

Basic Validators are trained to pick up on Obvious Tree Risk Features they can't help but notice as they go about their day to day work.

Basic Validators can also carry out Active Assessment at a Basic level, whenever they perform general 'inspection' procedures as part of their work.

If there's a red risk tree in County Durham, it's a Basic Validator who's most likely to spot it long before a Validator does.

*We're not keen on the word 'inspection' when it comes to tree risk. Inspection implies a level of detail that's seldom necessary if you're reasonable, proportionate, and reasonably practicable about managing the risk.

In DCC's case, the word 'inspection' is embedded in the description of many procedures carried out by Highways Officers, Rangers, and the like, so they've kept it.

Bark inclusions - A Feature or Fault?

Some nice evidence based arboriculture helping us move on from seeing bark inclusions as being 'Defects'.

Trees Adjust the Shape of Branch Unions to Increase Their Load-Bearing Capacity

Putting the benefit into risk

We're playing around with a new definition of risk.

It's inspired by CAPUR's, 'Improving Society's Management of Risks: A Statement of Principles.'

CAPUR's definition is…

"Risk an idea about what might happen in the future (good or bad)"

We very much like the clarity that 'risk' can be good or bad in this definition.

Mind you, I'm not sure what work 'in the future' is doing, that's not already done by 'what might happen'.

It'd be a better definition as.

"Risk an idea about what might happen (good or bad)"

I think it's much clearer definition of the threat v opportunity core of risk that ISO 31000's tries to encapsulate with its cryptic definition.

"Risk is the effect of uncertainty on objectives"

Both are leaps and bounds better than the most commonly used definition of risk…

"The likelihood of something bad happening"

There are no benefits to risk in this definition.

In VALID's risk model. An Acceptable risk is one where each year there are more than a million good outcomes for every bad outcome.

Think Safety Factor, not Strength Loss

To help stop unnecessary tree felling or damaging crown reduction tree work to your most important trees. We've updated and much improved our explanation of why t/R ratios don't work.

Think Safety Factor, not Strength Loss

Explains why you can't make a credible decision about Likelihood of Failure, or the risk, based on a residual wall thickness from, sonic tomography, micro-drills, or estimation with a sounding hammer.

Isn't t/R = 0.3 a guide? Or a starting point?
We've seen occasional comments like this on our social media feeds.

If Why t/R ratios don't work hasn't persuaded you, t/R = 0.3 doesn't work as a guide, or starting point. Here's some additional explanation about why.

t/R = 0.3 could be too much hollowness for a particular species of tree (Material properties). With particular crown dimensions and location (Load). And a particular stem diameter and geometry (Form).

Improve the Material properties, and t/R = 0.3 would be fine.

Or, lower the height, or have a more sheltered location (Load), and t/R = 0.3 would be fine.

Or, increase the section modulus by widening the diameter, and t/R = 0.3 would be fine.

t/R = 0.4 could be too much hollowness for a particular species of tree (Material properties). With particular crown dimensions and location (Load). And a particular stem diameter and geometry (Form)

...etc

And so forth, through every t/R ratio.

t/R = 0.3
A tree that's 50% hollow might be a tree with a good Residual Safety Factor.

t/R = 0.7
A tree that's 9% hollow might be a tree with a Residual Safety Factor that's too low.

Your critical t/R could be any ratio. It's just one part of the 'Form' in the tree Safety Factor puzzle.

When to use 'Why t/R ratios don't work'
You're welcome to use Why t/R ratios don't work to question tree felling or crown reductions when sonic tomography or micro-drill readouts are used to justify them.

Similarly, this will help you question media posts showing photos of stumps from felled trees, which are decayed or hollow, to justify the work.

Hollow stump porn

Sonic tomography, micro-drills, and sounding hammers can be a really useful kit. But, even when they're used well, they're only telling you a small part of the Likelihood of Failure story.

James Chambers at TMA, Paul Melarange at ThinkTrees, and Ian Barnes at Barnes Associates are concerned about poor Sonic Tomography leading to unnecessary tree felling or damaging crown reduction tree work.

To help those of you who get Sonic Tomography carried out by Picus, Arbotom, or ArborSonic, they've published this guide of what to look out for.

Sonic Tomography - Decay Detection Considerations

This is such a useful collaborative project, we'll forgive them for using the Safe word in it :-)

Here's a nice example of where a 'red line' is a 'red flag' in a tomogram.

t/R = 0.3 makes no sense.

t/R = 0.3 makes even less sense when the cross section is asymmetric.

Or when and the decay is off centre.

VALID's Risk Assessment Model

We're at the end of another successful tree risk training and advisory tour of NZ & AU. On this trip, we've been told some Aussie Arborists are not yet sure about upgrading their approach to tree risk with VALID because of a point raised in Peter Gray's Tree Risk Assessment Review for Arboriculture Australia's 'The Bark' magazine (2020).

Advantages & Disadvantages
In the article, Peter suggests a disadvantage of VALID is:

"The underlying mathematics running the App have not been made available for peer review. VALID claims to have used the services of a respected and independent maths professor to develop and test the App but this must be accepted without any chance to review and criticise it."

This 'disadvantage', is in fact an 'advantage'.

Here's why.

Our Risk Professor
First, the 'Maths Professor' is in fact a 'Risk Professor'.

He's Professor Willy Aspinall. Willy is the Cabot Professor in Natural Hazards & Risk Science at Bristol University, and he said this about the 'underlying maths'.

"We have stress-tested VALID and didn't find any gross, critical sensitivities.
In short, the mathematical basis of your approach is sufficiently robust and dependable for any practical purpose."

VALID is the only tree risk system that's been put together with a Risk Professor, who's an internationally distinguished expert in assessing risk in the natural environment. Surely, this is an 'advantage', and not a 'disadvantage'.

3 points about making the 'underlying maths' available.

1) It would give away our intellectual property, and anyone could copy it. Similarly, Google doesn't make its search algorithm available.

2) We're planning to write a paper with the Professor once he's less busy being an expert witness on the risk to Japanese nuclear reactors from an Aso volcano super-eruption.

Or on the fallout from the New Zealand Whakaari/White Island volcanic eruption.

3) How the TRAQ matrices are constructed and generate the risk is not peer reviewed.

How v5 of QTRA goes about calculating the risk and uses Monte Carlo simulations is not peer reviewed.

Another consideration is, the underlying maths won't help a Duty Holder or Risk Assessor with their decision-making. Some might think they know better and try to numberwang the model to game the risk they want. There are many examples of where this is done to the ISA's pre-TRAQ, Matheny & Clark, 'Hazard Rating' system.

We were also told, some Duty Holders and Arborists are concerned about how they would explain their decision making if they ended up in court.

If you use VALID, it's extremely unlikely you'll end up in court. If you did, as long as you don't make a green decision when it should be red - which is incredibly difficult to do - we've got your back.

The Bolitho Test

Don't do it

VALID's first ever publication was a Summer Branch Drop (SBD) Guide, way back in 2018.

The reason we got this guide out first was, in the UK we had a stinking hot dry spell in July 2018. It triggered many enquiries from Arborists and Duty Holders concerned the risk from SBD was something they needed to manage urgently. Otherwise they could end up in court. That unless they hastily erected signs, fenced trees off, or pruned them, they'd be liable if a death or injury happened.

Keen to bring some common sense to managing the risk from SBD. We rolled up our sleeves, did the research, and got the guide out within a couple of weeks.

5 years on, and we've updated our Summer Branch Drop Guide to v9. Mainly to include a section about why it's unwise to put up warning signs about Summer Branch Drop. We've had enough people ask whether we can make this point clearer and explain it. So we did.

Don't put up signs like this

As ever with our publications, we've waived copyright on the SBD Guide and released it under a creative commons licence. Anyone is free to use it.

The CliffsNotes
If your trees have no history of SBD, warning signs are unnecessary because the risk is Acceptable.

If you have a tree that has a history of SBD, and the risk is not Acceptable or Tolerable, warning signs are not an effective way to manage the risk.