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 Judgment. Not least because it looks like the Judge built his 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.
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.
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.
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.
The UK's Joanna Parker v The National Trust Judgment makes for interesting reading:
Parker v National Trust Judgment
Here, a crucial part of the evidence that supported The National Trust's defence was they had a tree risk management strategy* in place at Lyme Park, and carried it out.
Similarly, the National Tree Safety Group's (NTSG) 'Common Sense Risk Management of Trees', on which The National Trust's strategy was founded, looks like it was just as an important part of the evidence.
We wonder what the Judge in Cavanagh v Witley Parish Council might have made of that case if the experts had let him know the NTSG existed, and that they'd published, 'Common Sense Risk Management of Trees.'
Cavanagh v Witley Parish Council | A case of rough justice?
Here's a legal take on the Parker Judgment from Gabriel Fay at DWF LLP, that also explores its context in relation to the Cavanagh Judgment.
*Why's a Tree Risk-Benefit Management Strategy so important?
This paragraph, from an explanation of why the Tasmanian Government is adopting VALID's approach to tree risk, sums it up nicely.
"VALID is a complete Tree Risk-Benefit Management and Assessment system and not just another way of assessing tree risk. At its core is a Strategy that explains why and how the DSG is taking a reasonable, proportionate, and reasonably practicable approach to managing the risk from trees or branches falling. This establishes the context of any risk-benefit assessment. In the extremely unlikely event that a tree kills or injures someone on a state road, and there's a threat of legal or enforcement action, it's the Strategy that equips DSG with robust lines of defence about how they managed the risk."
Do 5 hopeless hedgehog cakes = 1 fantastic hedgehog cake?
Of course 5 one star cakes don't add up to 1 five star cake.
The reason why is you can't apply mathematical rules to qualitative ordinal ranks or scales when assessing tree risk - or assessing any risk, for that matter.
It's why having to suffer the film 'Sex in the City II' five times doesn't have the same value as enjoying 'The Godfather' once.
Similarly, applying mathematical rules to ill-defined words and saying things like High × Low = Medium is just as crazy as adding up hopeless hedgehog cakes when managing and assessing tree risk.
Risk experts know this well, but in the world of tree risk there are plenty of examples where hopeless hedgehog cakes are being added up.
Here, qualitative ordinal ranks or scales are added up, just like hopeless hedgehog cakes, in what the workbook calls a tree risk matrix (it's not a matrix, it's a table) to work out 'THE RISK'.
The authors of the 'Lantra Technical Award in Tree Inspection for Highways Workbook' are David Dowson and Jeremy Barrell.*
We recently had a discussion with Dave Dowson about adding up these hopeless hedgehog cakes to assess and manage tree risk on the UKTC discussion forum. In the interests of balance, you can catch Dave's response below. Our reply to that follows. The links also give you access to other comments in the discussion.
Dave Dowson's response
*The risk matrix (sic) is also peculiarly noteworthy because Jeremy Barrell has published that he thinks there are only two likelihood of occupancy zones. High and Low. Here, he has three targets, or likelihood of occupancy zones. High, Medium, and Low.
Can you help everyone manage tree risk?
We're after high quality obvious tree risk feature photos for a free multi-language App we're developing called Tree Alert. Full credit will be given to you as the photo source.
What is Tree Alert?
It's an App version of the free 'Obvious Tree Risk Features Guide.'*
Here are a couple of rough wireframe sketches to show you how it's looking in development.
We're after high quality photos of
1) Partial root failure
2) Broken or hanging branches
3) Cracks or splits
4) Advanced decline or death
5) Fungal brackets (an abundance of them)
6) Construction damage
As you'll see from the Guide, they need to VERY obvious.
If you can help by sharing any of these photos, please email them to email@example.com
Trees with the highest risk are the easiest to find.
When a tree has a risk that might not be Acceptable or Tolerable, it'll usually have an obvious tree risk feature that you can't help but notice.
High volume lower quality citizen science tree risk assessment is most likely to pick up 'red risk' trees before any scheduled visit from a trained Arborist carrying out 'Active Assessment.'
In VALID's free Tree Risk-Benefit Management Strategies, this is called 'Passive Assessment'. Passive Assessment is a duty holder's most valuable risk management asset because it can be done by anyone and it's going on day in day out.
Tree Alert will be used by your clients and members of the public, or Basic Validators, to alert duty holders or contact Arborists that they've seen a tree that might be 'dangerous'. The Tree Alert user will be able to check what they're looking at against a rogue's gallery of obvious tree risk features. If it matches one of them, they geolocate the tree and take several photos of the tree in its setting, and of the obvious tree risk feature.
The duty holder or contact Arborist will then get an alert with where the tree is and photos. A trained Arborist can then swipe right if they 'fancy' the tree and it needs a closer look, or swipe left if they reject the alert because it's not an obvious tree risk feature. Each alert will produce a brief photographic driven one-side report that will stand as a record of the alert.
*Obvious Tree Risk Features Guide. You can download and share the guide with your clients from the Risk Management page of our website.
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 been completing the move to their new VALID Strategy from July with Basic Drive-by Assessments being carried out in high use zones as part of their 5 yearly Active Assessment programme. They’ll soon be publishing their Strategy and we’ll share it when it goes live.
One piece of work they asked us to do in this project was to write a short briefing note for the General Manager State Roads, Department of State Growth (DSG), making the case for and explaining why they were upgrading their approach from QTRA to VALID. This is some of the work we were party to with DSG’s tree risk framework review team.
We’ve not shared this before because we thought it was a confidential bit of in-house work. However, it turns out this is not the case because the DSG is a government agency and 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:
During VALID's recent UK Summer tree risk training tour, I popped into Dunham Massey to check out the magnificent trees. Whilst walking amongst the Limes and Beech on the northern boundary, this is the sound of the traffic passing by.
Traffic Occupancy | High
I can't see the traffic because of the boundary wall, but I know the Likelihood of Occupancy on Smithy Lane (B5160) is High just by the sound.
The rhythm of this traffic is on average in the middle of High. Of course, traffic is messy and it pulses both higher and lower than the average during the one and half minutes of the recording, and during the day. But one of the many benefits of VALID is we've had a tame mathematician do the clever stuff and render complex traffic numberwang into easy to understand decision-making.
When you're a Validator, you'll have been calibrated so that you can make the O for Occupancy decisions for Very High, High, and Moderate based on what you can see (or hear) whilst you're on site.
You make this decision in the time it takes you to walk to the tree. You make it with your (calibrated) gut and it's effortless.
You're not expected to do any numberwang.
Or try to find traffic data that might not exist.
Or label it with a word that gives the illusion of communication and is open to interpretation.
If you're not sure about the Occupancy, then all you need to do is ask on the website's Community page and we'll tell you.
We know from the available data that the overall risk from Summer Branch Drop is mindbogglingly low.
The risk is so low, our risk of death from driving for the few minutes it takes to cover 3km/2mi is higher than from Summer Branch Drop over a whole year.
Yet, fear-mongering and threats from risk entrepreneurs about legal action if such a mindbogglingly low risk happens are pushing some anxious duty holders into wasting time and money on putting up confusing and ineffective signs; like this recent photo at Scone Palace, Scotland.
Not only are the costs of commissioning and managing these signs grossly disproportionate to any questionable reduction in a risk that's already Acceptable. Their ineffectiveness may backfire on the duty holder and create an opportunity for a risk entrepreneur to act as an expert in the extremely unlikely event of someone being injured or killed. It'd be all too easy for them to claim the duty holder hadn't managed the risk well enough with signs and they could've reduced it more by fencing or pruning. Or if the visitor wasn't an English speaker, why wasn't the sign translated into their language.
If you're a duty holder, or advise one, worry not about Summer Branch Drop and where, when, and how many signs to put up - or how many languages to use. We've got you covered with our handy Summer Branch Drop Guide on our Risk Management page.
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