This tree risk assessment review article by Peter Gray, from the Summer 2020 issue of Arboriculture Australia's 'The Bark', might be of interest to you.
We've grown up being told when we assess tree risk we should look out for tree 'defects'. The problem with this approach is what are commonly labelled as defects often aren't defects at all. Hollows, cavities, decay colonies, and deadwood, are natural features of older trees that are usually valuable habitat benefits. It’s seldom these natural features are risks that are not Acceptable or Tolerable. So, why are we labelling them defects before we carry out a risk assessment?
Those of you who know the origin story of VALID might remember the D-word dilemma. Vitality, Anatomy, Load, Identity are all neutral. On the other hand, because Defect means something that's a shortcoming, an imperfection, or a flaw it's not neutral. Defect is pejorative.
Defect is also a begging the question decision-making problem because usually, you can only work out whether a feature is a defect after you've evaluated it and the risk, not before.
Last year, the word ‘defect’ was removed from all of VALID’s Tree Risk-Benefit Management Strategies. Obvious Tree Defects was replaced by Obvious Tree Risk Features. Now, Defect is finally going to be removed as the D-word in VALID.
Occasionally, you'll come across an Arborist who claims to have anecdotal evidence about tree risk which they insist is the truth of the matter.
I've not given anecdotal evidence much weight. Not since I met a bloke down the pub who told me, it's not worth the paper it's not written on.
That said, having just read this article and its compelling evidence, I'm going to have to update my priors.
Can we rely on an expert witness telling us what the courts are expecting when it comes to tree risk?
In short, the answer is no because they’re an expert to the court, and not an expert for the court.
A competent arboricultural expert witness knows their limitations. Namely, their role is limited to being an expert to the court. They’re stepping way outside their field of expertise if they claim a Judge’s wisdom about how the law will evaluate tree risk-related evidence in the next case.
Claims by Arborists that they’re experts for the court should ring alarm bells. In a similar way to a Judge who, with no arboricultural training or qualifications, claims they could carry out an advanced tree risk assessment with a Static Load Test on a tree that has extensive root decay because they’ve seen it done.
In the UK, we’ve had several tree risk-related Judgments where the Judge has spotted an expert straying outside of their lane, and dipping into their legal dressing up box. Most recently in Colar v Highways England.
What’s of much greater concern is when a Judge is not aware that the evidence an expert gives them is critically short on expertise. Highly questionable expert evidence appears to have been pivotal in two landmark Judgments in the UK, Poll v Bartholomew and Cavanagh v Witley Parish Council.
This article explores the gulf between reasonable, proportionate, and reasonably practicable tree risk assessment and management, and expert evidence in these cases.
Recently, we had a couple of enquiries asking for a copy of this article. It reviews qualitative and quantitative approaches to tree risk assessment and looks at how we could do better.
It's over two years old now and was written at the time VALID was entering the home stretch. Though VALID has evolved further, much of the article is still relevant today.
This makes for an interesting tree risk assessment case study.
A TRAQ, QTRA, and VALID tree risk assessment were carried out on the same Pine trees in Western Springs, Auckland | NZ.
It involves around 200 Pinus radiata. From a risk of branch or tree failure perspective, the trees of particular interest are those that could fall onto a footpath or property.
The reports are linked.
TRAQ | August 2019
QTRA | December 2019
Random tree part or tree onto footpath
1/400,000 (Size Range 4)
1/500,000 (Size Range 3)
1/1,000,000 (Size Range 2)
<1/1,000,000 (Size Range1)
1 Not Acceptable
50 Not Tolerable
We’ve got an all new Basic Tree Risk Assessment workshop!
Contact us to arrange training now.
This one day course will train your staff in how to recognise obvious tree risk features that need a closer look by an Arborist. If you’re a tree owner or manager with staff who spend a lot of time outside, this is the most cost-effective way for you to manage your tree risk.
We know duty holders prefer this training to Lantra’s ‘Basic Tree Survey and Inspection’ or ‘Highway Tree Inspection’ courses. You'll appreciate the value because the training is all about helping you fulfil your duty of care as a key part of your Tree Risk-Benefit Management Strategy.
*Basic Validators aren’t expected to survey or inspect trees. They’re able to carry out Passive Assessment (keeping an eye out for obvious tree risk features you can’t help but notice). Or, carry out an Active Assessment at a Basic level, where they’re looking for obvious tree risk features.
If you have a tree in your garden, all you need do is download this short Strategy and use a pdf editor to change the personal details. Then keep an eye out for obvious tree risk features (page 3) that you can’t help but notice in high-use areas. If you see any of these obvious tree risk features, get in touch with an Arborist who's been trained in tree risk assessment.
When you know what to keep an eye out for, trees with the highest risk are the easiest to spot. Most tree risk assessment isn’t so difficult.
Here, and in the other Strategies, Passive Assessment encourages citizen science risk assessment from those who are on the front line, enjoying the benefits that trees give us, day in day out.
This, and the other Strategies for Government and Landowner, can be downloaded from our Risk Management page.
Don't call 'high-use' zones, 'high-risk' zones.
This is from the new edition of the Arboricultural Association's ARB Magazine that's out this week. It can be downloaded here.
The high tree risk twilight zone
As we’re going through a hot spell in the UK at the moment, it’s time to release v4.0 of the Summer Branch Drop (SBD) Guide.
Those of you who are concerned about the risk from SBD, this should help reassure you. The overall risk from SBD is mind-bogglingly low. In this update, we have an easy to grasp explanation of what mind-bogglingly low means. The overall risk from SBD for a whole year is the equivalent of the few minutes it takes to cover about 2 miles (3km) on a drive.
200 miles (320km) drive = 1 micromort (a one in a million chance of death).
The overall risk from SBD is over one hundred times lower than this.
If you’re a duty holder, unless you’ve got a tree that’s a repeat offender, there’s no need to fanny around with confusing and ineffectual warning signs. Just download the SBD Guide from the Government section on the Risk Management page of the website.
Photo credit - Paul Barton
If you'd like to stay in touch and be kept up to date with an occasional short and snappy newsletter every few months or so, please subscribe.
The kind of thing we'll share with you are some of the choice
cuts from this News page. We'll also let you know when there's
new training dates.
What is VALID?
© VALID is a not-for-profit organisation