Tree Risk News

  • 2022-04-15 6:23 PM | Admin (Administrator)

    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.

    Basic Tree Risk Assessment | Basic Validator Certificate

    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

    Basic Tree Risk Assessment | Basic Validator Guide

  • 2021-11-25 8:43 AM | Admin (Administrator)

    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.

    Cannonball Tree | Quebec

    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.

    QTRA Cannonball Tree Quebec

    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.

    Tomography Cannonball Tree Quebec

    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. 

  • 2021-11-13 8:44 PM | Admin (Administrator)

    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

    The high tree risk twilight zone

  • 2021-11-03 8:36 PM | Admin (Administrator)

    Cavanagh v Witley Parish Council | A case of rough justice?

    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 his decision on two flawed central pillars of expert evidence.

    Pillar 1
    Para 5 of the Judgment:

    "...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.

    Pillar 2
    The age of the fungal bracket.

    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.

  • 2021-10-28 5:37 PM | Admin (Administrator)

    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.

  • 2021-10-16 10:33 AM | Admin (Administrator)

    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.

    Joanna Parker v The National Trust | Lyme Park

    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.

    DWF | Joanna Parker v The National Trust

    *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."

    DSG Tree Risk Upgrade
  • 2021-09-21 6:25 PM | Admin (Administrator)

    Do 5 hopeless hedgehog cakes = 1 fantastic hedgehog cake?

    Tree Risk Matrix | Adding up 5 hopeless hedgehogs cakes to make one great hedgehog cakeOf 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.

    The most recent half-baked crime against risk and reason has been brought to our attention by concerned Highways Managers and Arborists in the 'Lantra Technical Award in Tree Inspection for Highways Workbook.'

    Lantra Tree Inspection for Highway | Tree Risk Matrix - David Down & Jeremy Barrell

    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.*

    *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.

  • 2021-09-06 2:32 PM | Admin (Administrator)

    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.

    Tree Alert App sketches

    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


    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, low effort, 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.

    Obvious Tree Risk Features Guide

    Tree Risk Management & Assessment | Obvious Tree Risk Features

  • 2021-08-30 10:43 AM | Admin (Administrator)

    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 (this has been upgraded to v8.0, which is linked):

    TAS Gov | QTRA to VALID Upgrade Explanation

    Tree Risk Management | QTRA to VALID Upgrade

    Tree Risk Management | QTRA to VALID Upgrade

  • 2021-07-28 9:21 PM | Admin (Administrator)

    We're now into a prolonged hot dry spell of weather. When this happens, anxious Duty Holders often get in touch about managing the risk from Summer Branch Drop (SBD), or Summer Limb Drop (SLD), or Sudden Branch Drop (SBD), or Sudden Limb Drop (SLD).

    What to do?
    The uncertainty about what to call SBD, or SLD, is often matched by similar uncertainty about how you should manage the risk.

    Should you put up signs?

    Fence trees off?

    Prune them?

    Fact-checking the risk
    The overall risk from SBD is mind-bogglingly low.

    From the data, the risk is so low, our risk of death from driving for the few minutes it takes to cover about 5km/3mi is higher than from SBD over a whole year.

    Finding a microscopic straw-coloured needle in a gargantuan haystackThe risk from Summer Branch Drop

    Despite this mind-bogglingly low risk, fear-mongering from Risk Entrepreneurs*, claiming legal action is likely if the risk were to happen and it wasn't managed or assessed, has had some anxious duty holders putting up confusing and ineffective signs.

    Is standing, lollygagging, or laying down fine?
    Tree Risk Management - Summer Limb Drop Sign | Summer Branch Drop

    What we know
    We know the overall level of risk from SBD is so low it's Acceptable.

    We also know, Arborists can't tell the difference between branches that have a high likelihood of failure from SBD, and those that have a low likelihood of failure.

    That means, warning signs make no measurable reduction to a risk that's already Acceptable.  In fact, the costs of commissioning and managing these signs are grossly disproportionate to any claimed reduction in the risk.

    Linger near trees at your perilSummer Branch Drop SignPhoto Credit - Paul Barton

    Exposing yourself in public
    Worse still, the ineffectiveness of these signs may backfire and create an opportunity for a Risk Entrepreneur to act as an expert witness in the extremely unlikely event of someone being killed or injured by SBD. It'd be all too easy for them to claim you hadn't managed the risk well enough, and you could've done more.

    Why didn't you put up more signs?

    Why didn't you fence the tree off?

    Why didn't you prune the tree?

    Or, if the visitor wasn't an English speaker, why didn't you translate the sign into other common languages?

    If you're a Duty Holder, or advise one, worry not. We've got your back on this one with our Summer Branch Drop Guide.

    An antidote to risk entrepreneurs
    Summer Branch Drop Guide

    In short, you don't need to do anything to manage the risk unless you have a repeat offender.

    We've also got a whole range of guidance of our Risk Management page.

    *Risk Entrepreneur
    "Treecare professionals who thrive on maximising the perception of risk in order to create standards for which they are perfectly placed to provide profitable solutions."
    Rick Haythornthwaite, Risk & Regulation Advisory Council

Stay up to date


© VALID is a not-for-profit organisation