Tree Risk News

  • 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

    QTRA to VALID Tree Risk Upgrade

    QTRA to VALID Tree Risk 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

  • 2021-07-19 12:36 PM | Admin (Administrator)

    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.

    High Traffic Occupancy

    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.

  • 2021-07-06 12:47 PM | Admin (Administrator)

    Here are 3 reasons to take the H(azard) word out of Tree Risk-Benefit Management and Assessment.

    Tree Risk Hazards?

    1) All trees are Hazardous
    The definition of a Hazard is something that has the "potential to cause death, injury, or damage".

    The informal and common interpretation of a Hazard is, it's a risk that's unacceptable and needs to be mitigated. The hazard needs to be managed in some way. 

    Because every tree has the potential to cause death or injury, or damage property, every tree is a Hazard. No matter how Acceptable or Tolerable the risk.

    2) Hazard thinking is risk and benefit averse
    Risk averse thinking and decision making is about what's the worst that could happen?

    The worst that could happen is only limited by how easily you can imagine the worst case scenario. Our brains might be marvels of nature, but we've evolved to first imagine the worst because it's a useful survival tool. If you're on the first rungs of the evolutionary ladder and on the plains of Africa, it makes sense to respond to the long grass rustling as though it's a Lion rather than analyse the evidence further. Our instinctive gut reaction to a Hazard is, you need to do something about it.

    Instinctively thinking with your gut is the opposite of a risk literate frame of mind. Risk literacy is about your mind overriding your gut instinct and considering what's most likely to happen. There's a risk. Is it an Acceptable or Tolerable risk?

    The benefits of trees don't get a look in with Hazard framed decision making. It's all negative, with no positive risk.

    3) Hazard can easily be weaponized and used against you
    This is neatly illustrated in Mike Garvey's International Society of Arboriculture conference presentation, 'Did we keep that Heritage Tree Too Long?

    Here, Mike looks at the legal case of a branch from a Cottonwood that falls and severely injures someone in a Municipal Park.

    The link below takes you to 16'55'' of the presentation on the ISA's YouTube channel (you'll likely get an Ad first). There, you'll see how easily the Claimant's Attorney weaponizes the H word.

    The line of attack the Attorney goes for by honing and wielding the H word is the same reason we're taking the D(efect) word out of Tree Risk-Benefit Management.

    These are some of the reasons why the H word doesn't appear in any of VALID's publications.

  • 2021-06-27 10:46 PM | Admin (Administrator)

    It’s always valuable to see how others view your work because they’re seeing it with different eyes.

    We were recently asked by a State Government client to publish a standalone summary of our Tree Risk-Benefit Management Strategy because it was the easiest way for their senior managers to understand how they were updating their approach to managing the risk.

    The Strategy Summary is now available on the Home and Risk Management pages of our website.

    Tree Risk Management Strategy | Policy & Plan Summary

  • 2021-06-06 3:54 PM | Admin (Administrator)

    We're updating all our publications from Tree Risk-Benefit Assessment & Management to Tree Risk-Benefit Management and Assessment.


    We thought we'd gotten past looking at tree risk through the eyes of an Arborist, rather than a Duty Holder, with v5.0 of the Strategy. This is where creating a flowchart helped reveal that the most valuable risk management asset is Passive Assessment by anyone. Not Active Assessment by an Arborist.

    A 5 yearly Active Assessment isn't being topped up by Passive Assessment, as we used to propose. Passive Assessment is being carried out all of the time, day in day out. It's being topped up by Active Assessment in zones of high confluence every 5 years.

    Well, in the process of completing our work helping the Tasmanian Government manage their tree risk, David was asked whether we could produce a summary to explain what VALID is about. It's for the strategic decision-makers, they explained.

    "'What is VALID?', does that", David said.

    "In 'What is VALID?', the first picture is of a woman looking at a VALID likelihood of failure decision in the Tree Risk App. That's an Active Assessment at a Detailed level", they replied.

    "That level of investigation is not the first thing in the minds of Tasmanian Government decision-makers when it comes to adopting VALID's approach to Tree Risk-Benefit Management, is it?"

    They're right.

    Hence the upgrade and the new, 'What is VALID?'

    Tree Risk Management & Assessment | What is VALID?

  • 2021-05-24 11:38 AM | Admin (Administrator)

    Jeremy Barrell’s Arb Magazine version of his journal article has been posted by the Arboricultural Association, on their website, as a 'Legal Update' - it's not a legal update, it's an opinion piece by an Arborist.

    It's had some Duty Holders and Arborists ask us about where his binary, ‘High’ or ‘Low’ likelihood of occupancy approach sits with VALID's Likelihood of Occupancy categories.

    To recap. The heart of Jeremy Barrell's journal article are three legal cases cherry-picked by Jeremy, where Jeremy acted as an expert, and are Jeremy’s interpretations of these cases where Jeremy’s evidence was a key factor.

    When we first went through the article, we were disappointed to find it appeared to be less about reasonable, proportionate, and reasonably practicable tree risk-benefit management (which is surely what the Courts and Coroners are after). And more about setting out what Jeremy expects to contest when he's employed as an ‘expert witness’. 

    Jeremy Barrell Tree Risk Management Article

    Back to the binary ‘High’ v ‘Low’ likelihood of occupancy.

    VALID’s Likelihood of Occupancy categories are based on log base 10, like the Richter scale uses to measure earthquakes. If we show the likelihood of occupancy to scale as 10 x 10 canvases, and set High at the centre, we can compare VALID’s and Jeremy’s likelihood of occupancy categories.

    Likelihood of Occupancy | Tree Risk Management

    Jeremy Barrell Tree Risk Management | Likelihood of Occupancy

    Jeremy’s High occupancy spans 4 Richter Scale orders of magnitude with a range of ×10 000!

    Or, another way of looking at it. A Richter scale 4 earthquake is categorised the same as a Richter scale 7 earthquake.

  • 2021-04-26 8:23 AM | Admin (Administrator)

    In the previous post we looked at VALID's Goldilocks Likelihood of Occupancy canvases to explore categories that are not too wide, and not too narrow, that are just right.

    These Likelihood of Occupancy canvases are helpful when we look at tree risk management and assessment decision-making in the UK’s landmark Poll v Bartholomew Judgment.

    Poll v Bartholomew - VALID Likelihood of Occupancy

    In Poll, a motorcyclist was seriously injured by a falling Ash stem. The Judge found for the Claimant because the experts said the tree was ‘High Risk.’

    In their reports, the Claimant’s expert said the tree was ‘High Risk’. The Defendant’s expert didn’t mention any level risk. Yet in their Joint Statement, the experts agreed the tree was a ‘Medium Risk.’

    Naturally, the experts' opinions left the court scratching its head. The court had to ask them to produce a Second Joint Statement to define what they meant by High, Medium, and Low Risk, and what risk the tree posed.

    In the Second Joint Statement, the experts told the court the tree was ‘High Risk’. However, they concluded the risk was high after they'd assessed the Likelihood of Occupancy for a minor country road at 50%, when in fact it was 1%. The experts overvalued the occupancy by a whopping factor of 50. This gaffe was so enormous the tree was in fact a ‘Medium Risk’ and not a ‘High Risk.’

    The Judge would’ve found for the Defendant, not the Claimant, if the tree was a ‘Medium Risk.

    Poll v Bartholomew | Expert Evidence - Likelihood of Occupancy

  • 2021-04-26 8:01 AM | Admin (Administrator)

    In the Scale of the Problem we saw the overall risk from branches and trees falling is so extremely low we need a microscope to see it.

    Tree risk spectruem

    The only sensible way to measure risks that go this low is to use a logarithmic scale.  It turns out the Goldilocks logarithmic scale for tree risk that’s not too narrow, and not too wide, that's just right is log base 10.  Just like the Richter Scale is for measuring earthquakes.

    So far so numberwang. What does that mean for you?

    Well, when it comes to Likelihood of Occupancy decision-making, the advantages of log base 10 are obvious when drawn to scale.  There’s 5 colour-coded Likelihood of Occupancy categories in VALID.  If we centre High, then you can only see a bit of the heel of Very High.  Nearly all of it’s off the screen.  You can make sense of Moderate but you can barely make out Low.  And you can’t see Very Low at all.

    Tree Risk-Benefit Management & Assessment | Likelihood of

    So, the first decision a Validator makes with Likelihood of Occupancy is what 3 categories can’t it be?  Which 3 make no sense?  Once calibrated this is an effortless decision. Then it comes down to one of two. Usually, which one is the most obvious because they're huge canvases.  If in doubt you go for the higher one.

  • 2021-03-29 7:49 AM | Admin (Administrator)

    We regularly use visuals to convey both the context of tree risk and how you can measure it. Recently, we shared a post with Professor David Ball's quote that the prospects of reducing the risk below the current level were comparable to finding a microscopic needle in a gargantuan haystack.

    To help convey that finding a microscopic needle in a gargantuan haystack simile further, we've had a play around with illustrating the tree risk context using coloured spectrums.

    In the graphic, the top spectrum shows the reality of tree risk to scale. We know that compared to other everyday risks we readily accept, the overall risk to us from branches or trees falling is extremely low. Our annual risk of being killed or seriously injured is less than one in a million. At this scale, we can't see the amber and red risks. We'd need a microscopic.

    If we take the risk spectrum to a scale where we can just make out the risks that we're trying to find and manage, we have to overvalue the base-rate risk by a factor of more than 1000.

    Tree Risk Management | Tree Risk Spectrum

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