Tree Risk News

Here's the new VALID Likelihood of Failure voting card for v2 of the Tree Risk App, which is in development.

If it's new to you, VALID (from where we get our name) gives you 5 chapter headings and 15 subheadings, that can affect a tree's Likelihood of Failure.

When you're carrying out a tree risk assessment, and have got to the tough Likelihood of Failure decision, VALID gives you a structure that guides through the factors you should consider.

At its simplest level, VALID is a checklist of things to think about and you're welcome to this voting card we use in training.

The most important change is:

DEFECT to DECAY
We'll finally be rid of any mention of the red DEFECT word in VALID's publications. Those of you who have been there from the beginning will know this has been a quest for some time.

The first subheading under DEFECT is section modulus. That's because if you don't have a grasp of section modulus, and are relying on t/R ratios, you can't make a reasonable decision about the significance of strength loss from decay.

If you're not a Validator, who's been trained to use the Tree Risk App, here's their guide on how they go about using the current version to get to a base rate colour. You should get a sense about how this elegant and sophisticated approach helps you with your likelihood of failure decision making from this.

Likelihood of Failure | Decision Making

Day 2 of Validator tree risk training is all about making robust Likelihood of Failure decisions. If you follow this guide, it's really difficult to get it wrong. If anyone tries to game the risk to get it where they want it to be, it's really obvious where they've got it wrong, and that's what they've done.

In this famous scene from 'Marathon Man', Laurence Olivier finds himself in the uncommon position of playing a retired Nazi Holocaust Dentist. 'The White Angel' escaped Germany with a cluster of stolen diamonds. He's not happy though, because he thinks his retirement stash is threatened. To find out whether it is, he's about to torture a tethered Dustin Hoffman by inflicting pain with a dental scaler, and giving relief with oil of cloves (ISO 31000?). The torment begins with him repeatedly asking, in an increasingly menacing tone

"Is it safe?"

"Is It Safe?"

"IS. IT. SAFE?"

Arborists and Urban Foresters are similarly tortured when they're asked about trees.

"Is it safe?"

They'll be asked.

Well, is it or isn't it?

Safe, to just about anyone, means a complete absence of risk.

"Is it safe?", is a binary trap. If you answer, "Yes", and the tree then falls and kills, injures, or damages property, no matter how low the risk, clearly the tree wasn't safe.

Safe enough?
Even if you reframe the question by answering, "It's safe enough". Or, "It's as safe as necessary". What they'll hear and remember is the word 'safe', and safe to just about everyone means a complete absence of risk. What they won't hear, or will instantly forget is the all-important qualifying 'enough' or 'necessary'.

Better safe than sorry
Safe and safety are words that are all too vulnerable to being weaponised with hindsight or outcome bias as failures in the duty of care if a risk is realised. More than that, they can hamstring critical thinking. 'Better safe than sorry,' easily trips off the tongue without a second thought about what it really means. Or the unintended consequences of trying to achieve it. "Could we make it safer?" sounds like a reasonable request.

Mind your language
The language you use when talking about tree risk is really important. You can't make a tree safe. You can't remove all of the risk. But you can always make a tree safer by cutting some of it off. If we stick with risk words, we can diffuse lazy phrases like, 'Better safe than sorry' or 'If in doubt, take it out', because it translates to 'Better no trees, or less tree, than any risk.'

If the risk from a tree is Acceptable or Tolerable, there's no reason to make it safer by cutting bits of it off. It's why you won't find the 'S' word in any of VALID's Tree Risk-Benefit Assessment and Management publications.

This is quite a long explanatory post, so here's the take home message:

VALID represents a responsible body of competent professional Duty Holders, Validators, and Basic Validators who would agree there were no Obvious Tree Risk Features on the Cherry Tree in Hoyle v Hampshire County Council.  This tree did not have any obvious defects.  All the so called defects were natural features.

Here's how we get there
The Bolitho Test is a new one for us, which we think is profoundly important. From the recent Hoyle v Hampshire County Council Judgment in the UK:

"Principal issues for determination
Para 32

(iii) was Mr. Soffe's/Mr. Power's VTA of tree 572 such that no competent Tree Inspector would have completed it in this way.

Para 114

…the Claimant must show that no responsible body of competent professional tree inspectors would have come to the conclusions and made the recommendations…

(Bolitho v City & Hackney Health Authority)"

What's a responsible body of competent professional tree inspectors?
This is saying for the claim of negligence to stick, for an edge tree, with a natural lean and asymmetric crown, without noteworthy buttressing on the sheltered side, next to a ditch, to be considered anything other than normal features, NO competent Arborist would agree with this.

Or to put it another way. EVERY other competent Arborist would need to agree that an edge tree, with a lean and asymmetric crown, without noteworthy buttressing on the sheltered side, next to a ditch, are not normal features. That they're a catalogue of 'obvious defects' that means you need to explore for roots on the sheltered side.

Strategy - your first line of defence
In VALID's Tree Risk-Benefit Management Strategies, we define what obvious risk features we're looking for in a tree (the word defect does not appear in any of the Strategies because it's a begging the question fallacy). The Obvious Tree Risk Features Guide is a free resource that's released under a creative commons license. Anyone is welcome to use it.

Nothing to see here
An edge tree, with a lean, asymmetric crown, lack of noteworthy buttressing on the sheltered side, next to a ditch has NO Obvious Tree Risk Features.

How many competent professionals?
Now, we're tree risk experts, not lawyers. But, reading about The Bolitho Test, it looks like the weight of a 'responsible body of competent professionals' needs to be more than AN Other. Which is fine, because if we took a random sample of 100 Validators, (responsible body of competent professionals) we'd be surprised if any of them would've taken a closer look at the tree in question.

The Cherry tree was an Acceptable risk at a Passive level of assessment, and at a Basic level of Active Assessment.

What lies beneath
We know Ivy (and other vegetation that obscures the stem) can cause concern amongst some Arborists who assess tree risk. They feel they have to remove this vegetation because of what risk feature it might hide. We disagree, unless there's an Obvious Tree Risk Feature to trigger it's removal. This example from the Government Agency Strategy describes how a Validator deals with this kind of vegetation when carrying out an Active Assessment at a Basic level.

"We won't remove climbing plants, undergrowth, basal epicormic growth, or cut hedgerows to get a closer look unless there's an Obvious Tree Risk Feature. It's only if we find these features the costs of removing vegetation, and loss of habitat benefits, are justified."

A responsible body of competent professionals
We've got a large and growing international group of Duty Holders, Validators, and Basic Validators (responsible body of competent professionals) who manage and assess tree risk without removing vegetation, unless there's a trigger to justify it.

No matter how many natural features are being labelled as obvious defects because they appeared in a recent Judgment, Inquest, or Enforcement, and added to tree inspection training programs and publications, VALID is happy to share a responsible body of competent professionals that would take a very different view when it comes to managing and assessing tree risk.

This recent UK civil case is about the death of David Hoyle. Sadly, he was killed when a Cherry tree uprooted during foul weather and struck his car as he was driving along the A287 in Hampshire, UK.

There's a short article about the Judgment in the Local Government Lawyer.

Here's the Judgment:

Hoyle v Hampshire County Council

The claim was successfully defended. From a tree risk perspective, it looks like key parts of the defence were:

1 Tree Risk Strategy
Like the recent Parker v The National Trust Judgment, Hampshire County Council had a Tree Risk Strategy and followed it.

2 Tree Benefits
The Strategy included the benefits from trees. The Judge makes a particular note about the benefits from trees when balancing them with the risk.

3 Obvious Tree Risk Features
Most importantly, the tree had no Obvious Tree Risk Features.

The Claimant's Evidence
The Claimant's expert is Jeremy Barrell, and we find some of his evidence alarming.

An edge tree with an asymmetric crown is described as a defect. It isn't a defect. It's a normal feature.

An edge tree with a lean is described as a defect. It isn't a defect. It's a normal feature.

An edge tree with a lack of root 'buttressing' on the sheltered side is described as a defect showing a lack of roots. It isn't a defect. It's a normal feature.

Risk Assessments
The tree was risk assessed as part of a Drive-by Assessment, 16 times in the previous 16 months.

In the year before the tragedy, the tree was risk assessed twice by qualified Arborists. A Countryside Department inspection of the tree, and a Highways negative inspection of all the trees on the A287. Neither Arborist regarded the tree as having a risk that needed reducing.

Reasonable, Proportionate, and Reasonably Practicable
That this Claim made it to court, and David Hoyle's family and friends have been led to believe that his tragic death could've reasonably been avoided is concerning.

Tree Risk-Benefit Management Strategy
From the tree's description in the Judgment, we can't find any reason why the tree justified a Detailed Assessment. The tree didn't need a closer a look, so the expense of carrying out a Detailed Assessment doesn't look like it was reasonable, proportionate, or reasonably practicable.

The Bolitho Test
We've got an additional post about the important role The Bolitho Test played in Hoyle v Hampshire County Council, here.

UPDATE
We've recently updated this:

It's because we've done some fine tuning to the Basic Validator guidance that's connected to it. We were also asked to clarify some of the points in it.  Here's the text from the original post.

As some of you are aware, the Tasmanian Government (State Roads) was an earlier adopter of VALID’s approach to tree risk-benefit management and assessment.

They’ve completed their move to a VALID Strategy from July. Basic Drive-by Assessments are carried out in high use zones as part of their 5 yearly Active Assessment programme.

One piece of work they asked us to do in this project was write a short briefing note for the General Manager State Roads, Department of State Growth (DSG).

The briefing note is to make the case for and explain why they were upgrading their approach from QTRA to VALID.

We’ve not shared this before because we thought it was a confidential bit of in-house work for DSG’s tree risk framework review team.

However, it turns out it's not confidential because the DSG is a government agency. The work is in the public domain.

As many of you working at the tree risk coalface might find it of interest, we’re now sharing. and you can download it here:

On the recent epic tour Downunder (more on this later) we trained a whole bunch of Basic Validators for SA Power Networks, SA Water, and Catholic Education Tasmania.

Whilst working with these organisations, we've created standalone guidance and have colour coded everything for a Basic Validator with the same company blue we use for the Tree Risk-Benefit | Basic Validator logo on their certificates.

The blue colouring will make it a sintch to distinguish between Validator and Basic Validator guidance at a glance.

Not sure what a Basic Validator is?

It's someone who's not an Arborist that's been trained to pick up Obvious Tree Risk Features they can't help but notice as they go about their daily routine. They mainly carry out Passive Assessment. If necessary, they can carry out Active Assessment at a Basic level.

After having a Tree Risk-Benefit Management Strategy in place. Basic Validators are a Duty Holder's most valuable tree risk asset because if there's a risk that's Not Acceptable or Not Tolerable, it'll be a Basic Validator who'll most likely pick it up first.

Basic Validators don't make decisions about whether the risk is Not Acceptable or Not Tolerable. They just flag trees that need a closer look by an Arborist.

Basic Validator Guide

This tale about the felling of the famous Cannonball Tree in Quebec because the risk was too high has some incongruous tree risk elements to it.

We've not been able to get hold of the reports behind this decision. Only what's in a Press Release and accompanying PowerPoint.

Cannonball Press Release

Cannonball PowerPoint - has been through translation software from French to English.

These are the main curiosities.

1) The range of risk is estimated (sic) with QTRA as being between 1 in 35 and 1 in 526. Both these two and three significant figure risks values are so accurate for a risk that has so much uncertainty, they're not credible.

2) The two tomograms from 2009 and 2020 in the PowerPoint are clearly from different heights. As ever, the tomograms appear to undervalue the all the important outermost wood which carries the most load, and is often the strongest and stiffest part of the tree.

3) It looks like 73% of the cross section decayed is beyond some kind of threshold, which isn't explained. There's no sound basis for making a decision about the safety factor of a cross-section in a tree based on the percentage decayed without considering the wind load, geometry, and material properties. 

The recent Parker v The National Trust Judgment in the UK spends some time examining the history of the National Trust's tree risk management strategy. That includes many references to 'risk zones', when what they mean and should say is, 'use zones'.

This is the same 'begging the question' logical fallacy that looks like it influenced the Judge's decision-making in the Cavanagh v Witley Parish Council Judgment.

Zones of use being conflated and confused with risk or hazard is a common error we're regularly seeing in tree risk management strategies. This re-up is a short article, published last year in the Arboricultural Association's ARB Magazine, explaining why you should mind your language when managing tree risk and zoning.

The high tree risk twilight zone

Many of us in the UK have misgivings about the landmark Cavanagh v Witley Parish Council Judgment. Not least because it looks like the Judge built their decision on two flawed central pillars of expert evidence.

"...The presence of a fungal bracket at or near the base of a tree is a sure sign of impending failure and would have mandated emergency treatment; most likely felling of the tree."

The presence of a fungal bracket most emphatically isn't a sure sign of impending failure. This point in the claim isn't contested by the defendants in the Judgment.

Witley PC's expert persuades the Judge they can accurately age the fungal bracket from the number of pore tube layers. An expert to the court should know you can't do this. The bracket could've been as young as about one year, or much older.

From the above evidence, it looks like the Judge had little choice but to prefer the shortest inspection frequency offered by the experts that would find the bracket. Which was 18 months to 2 years.

The Judgment appears to be flawed because key evidence is flawed. Not least because if we extend the logic of Pillar 1, we need to inspect high-risk trees (sic) in high-risk zones (sic) every day, between spring and late autumn, in case they've produced a fungal bracket and failure is 'impending.'

We explore the role of these key pillars of expert evidence, and more, in this LinkedIn article. It also takes a wider perspective of expert witness evidence, tree risk, and court Judgments in the UK.

Cavanagh v Witley Parish Council | Case of Rough Justice

To get a better understanding of what evidence the Judge had to work with, we asked DWF (Solicitors for Witley PC) whether they would release the expert reports and joint statement. The experts refused to disclose their reports.

We then made a formal request under the Environmental Information Regulations (2004) to Witley PC. They referred me to DWF, who reported back that the experts refused to share the contents and disclosure couldn't be forced under the Act. Similarly, Witley PC's insurers said they cannot release the expert reports without their permission.

Finally, under the impression that a Civil Judgment (and Appeal) meant the expert reports are in the public domain, we applied to the Queens Bench Division. After what has been well over a year, they finally got back to us and said expert reports in Civil Judgments are not public property.

In VALID's Tree Risk-Benefit Management Strategy templates, apart from emergency work there are NO timescales for risk reduction work.

Here's why:

1) By setting work completion dates like 7 days, 10 working days, 4 weeks, 13 weeks, 3 months, or 6 Months (these are from real examples), you're quantifying the likelihood of failure part of the risk assessment with a mind-blowing accuracy that's simply not credible.

2) By giving a very specific period within which risk reduction work should be carried out, this is what you're effectively saying. The risk is not Acceptable or Tolerable. But, the risk is Acceptable or Tolerable for those periods of time. Then, suddenly, the risk is immediately no longer Acceptable or Tolerable after the last day.

3) If the risk is realised before the work completion date, then self-evidently your timeframe when the risk is temporarily Acceptable or Tolerable was wrong.

4) If your client can't get the work done within these dates, and the risk is realised, then they're hung out to dry.

5) You're unlikely to know what competing demands there are on your client's budget.