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

Establishing the context

Sometimes, the gulf between reasonable, proportionate, and reasonably practicable tree risk management and assessment, and expert evidence in UK court Judgments is vast. So vast, it's difficult to believe they're speaking the same language. This wide gap has been of considerable concern to many in the profession since back in the days of the 2006 Poll v Bartholomew Judgment.

In Poll, the experts jointly assessed the risk of an Ash stem falling onto a country road and severely injuring a motorcyclist. They advised the court the likelihood of occupancy on this minor road country road was 50%. When in fact it was only 1%. To help you visualise just how big the gap is between these two figures, it's the difference between a vehicle passing you about every few seconds and every 4-5 minutes, during the working day.

Likelihood of Occupancy as log base x10 canvases

This whopping margin of error, by a factor of 50, seems to have been the pivotal evidence in Poll. The gaffe was so great it meant the court was told the Ash tree was a high risk, instead of medium or low risk, and the Judge found in favour of the Claimant.

Poll created such substantial fallout, with reports of trees in the countryside being unnecessarily felled and concern raised about the liability of underwriting landowners, that it became a catalyst to the formation of the National Tree Safety Group (NTSG). Thankfully, the NTSG has brought some much needed common sense to tree risk management since it was formed in 2007.

Similarly, the Risk and Regulation Advisory Council (RRAC), which was founded to address the poor handling of public risk, also contributed to a better understanding of tree risk on two counts. First, its 2009 guides, reports, and tools about risk management, and in particular public risk, which included the subject of tree risk as one of its 'Risk Aversion' case studies. Second, when it was quick out of the blocks to recognise the 'disproportion' and role of "risk entrepreneurs"* behind the ill-fated BS 8516 Recommendations for tree safety inspection, and its 5-yearly inspection proposal. With much national media coverage, the RRAC publicly put BS 8516 to the sword in 2008.

*Risk entrepreneurs - "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."

The work by the NTSG and RRAC has been ground-breaking, enlightening, and welcome. Despite their efforts, by the time of 'Cavanagh' the gulf between reasonable, proportionate, and reasonably practicable tree risk management and assessment, and expert evidence doesn't appear to have narrowed in the 10 years since Poll.

The Cavanagh Judgment

In a previous article, The high tree risk twilight zone, I explored the 'begging the question fallacy' of high-risk zones and high-risk trees, which likely had some influence on the Cavanagh v Witley Parish Council Judgment. If you've not read this short article yet, I'd recommend you have a quick look by clicking the link because it explains why high-risk is italicised throughout this one. In short, it illustrates the problems that come from labelling high-use zones, high-risk zones, and large trees, high-risk trees. Conflating these terms means that no matter how low the risk might be, if the risk is realised and someone is injured it's very difficult to accept that the risk wasn't high. In this second piece about Cavanagh, we're going to examine what appears to be rotten at the roots of the evidence presented to the court.

Witley, 3rd January 2012

To briefly recap Cavanagh. Witley Parish Council were the duty holders and responsible for a mature Lime (Tilia) tree that fell into the road during severe weather. Sad to say, the tree hit a bus that was passing at the time and severely injured the driver, Mr Cavanagh. Judge MacDuff concluded that Witley's policy of inspecting higher-risk large mature trees in such high-risk zones every 3 years was inadequate. The Lime should've been inspected at least every 2 years, and preferably every 18 months (in and out of leaf), and the Judge found in favour of the Claimant, Mr Cavanagh.

How did the Judge get there?

When you read through the Judgment carefully, the reasoning of the Judge appears to be pretty clear about how he gets to his preferred inspection frequency of every 2 years. Given the evidence presented to the court by the experts, it's the logical conclusion for him to have drawn. Let's go through the key evidence, step-by-step.

First, these dates are important.

Summer 2009 - The tree was inspected and there was no fungal bracket present.

January 2012 - The tree failed and a Ganoderma fungal bracket was present.

The single most revealing sentence of the Judgment is in para 5, which is part of the Claimant's case.

“...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.”

We could just stop there. That, in 2016 a court is being told the mere presence of fungal bracket 'is a sure sign of impending failure' and the need for 'emergency felling' is astonishing. It's demonstrably nonsense of the highest order. It has no basis in fact and shouldn't be part of any credible opinion; particularly one from an expert to the court. For those of you who aren't Arborists, here's why.

The tree & the fungal bracket (top left)

Fungus is not the Bogeyman

The presence of a fungal bracket most emphatically does not mean 'a sure sign of impending failure and emergency felling.' There are countless trees around the country that are getting on just fine providing fungal brackets with a home for many years, and decades, that haven't failed; for veteran trees, this has likely been centuries. Hosting some decay is perfectly normal for a Lime tree of this age, history of pruning, and setting, and it seldom affects its likelihood of failure. In fact, it'd be quite remarkable if such a tree wasn't colonised by some decay, whether or not a fungal bracket was present.

Trees and decay fungi mostly live happily together and decay only becomes a problem when it's very extensive, or if the tree has low vitality. The real significance of a fungal bracket is that it's an 'obvious tree risk feature' inviting you to have a closer look. You're taking a closer look to find out whether the tree has enough sound wood and vitality that it can comfortably accommodate the fungus and associated decay.

To add another a couple of points. From photographs I've seen of the stump shortly after the accident, it looks like the primary failure was at the roots, and the fungal bracket is described as being 300mm up the stem in the evidence. It's a very real possibility the fungus that decayed the roots is a different species, or a different colony, to the one that fruited and produced the bracket. Also, the roots that failed in 2012 would likely have hosted significant decay at the time of the 2009 inspection; a point not considered in the Judgment.

Unfortunately, with our standard of tree risk expertise bar now set so low by equating a fungal bracket with impending failure, things don't get much better.

The Defendant's own goal

Para 6 of the Judgment is Witley's defence. This largely rests on the fact that the fungal bracket wasn't there at the time of the 2009 inspection. Remarkably, there's no rebuttal of the claim that, "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." If we ignore that elephant in the room, you can kind of follow the thinking about why the age of the fungal bracket is important. A 3 yearly inspection cycle is perfectly reasonable. That the fungal bracket first appeared in the autumn of 2009, just after the last inspection was unfortunate. It's unfortunate because the fungal bracket would've been picked up in a few months' time during the next scheduled inspection, in the summer of 2012. As we're about to see, this line of argument that focuses on the age of the fungal bracket, and not contesting it as a sure sign of impending failure, backfires. Before that, let's look at the science behind ageing a fungal bracket.

What's in an age?

The Defendant's expert said the fungal bracket first appeared in the late summer of 2009, just after the last inspection. They aged it at 3 years of growth by counting the number of pore tube layers (the light brown striped layers in the example image below) when they visited the stump in November 2012. One pore tube layer for each year of growth in late summer 2009, 2010, and 2011. There are three problems here.

How old is this fungal bracket? One, two, five years?

1) You can't count pore tube layers, like the candles on a birthday cake, to accurately age a fungal bracket. Perennial fungal brackets don't grow like trees that produce an annual ring each year. They often produce a new layer of pore tubes with each growth spurt. This can happen once, twice, maybe several times a year. Some years there's no growth. Other years there's growth but just the darker brown flesh and no pore tube layer. Those of you who may have heard anecdotal evidence that you can age fungal brackets like this, don't take my word for it. We can ask someone who's an internationally renowned mycologist with particular expertise in decay fungi.

“Layers of pores/tubes on perennial brackets of fungi cannot be reliably used to judge age, because there is not necessarily just one new set per year. There could be several, or perhaps even no new pores”

Professor Lynne Boddy, Cardiff University

2) Fungal brackets are not all born in late summer.

3) The tree failed in January 2012. Yet, the fungal bracket wasn't aged until some 10 months later, in November 2012. By the expert's own metric of ageing, the fungal bracket would've put on another layer of pore tubes in later summer 2012 - fungal brackets usually keep on growing after trees fail. That means, according to their expertise, with 3 pore tube layers, it first appeared in the late summer of 2010 and not 2009, just after the last inspection.

Some additional fact checks are worth considering here that affect the ageing. Fungal brackets often put on growth spurts after trees have fallen. They do this because whilst the tree's alive, the resource-rich outermost functional wood is usually too wet and there's not enough air for fungi to colonise it. However, once a tree falls and dies, the functional wood becomes dysfunctional when the water content lowers and it becomes aerated. This fresh dysfunctional wood becomes a much more hospitable environment for some decay fungi, and they can thrive in the newly released resource. What that means is it's entirely feasible that the fungal bracket enjoyed 2 growth spurts, and produced 2 more pore tube layers during 2012, after it failed. The fungal bracket, with 3 pore tube layers, may have been as young as a year or so when it was aged in November 2012.

Lining up the ducks

The court has the following evidence to work with.

• The Lime was a high-risk (or higher-risk, as the Judge put it) tree growing next to a high-risk road.
• The tree had a fungal bracket, which 'is a sure sign of impending failure', that had 3 years of growth since late summer 2009.
• Witley's inspection frequency was every 3 years.
• The last inspection was the summer of 2009, just before the fungal bracket appeared.
• The next inspection was scheduled for the summer of 2012, and this would've found the fungal bracket.
• The tree failed and severely injured Mr Cavanagh in January 2012.

Of all the inspection cycles raised by the experts, the one which would've found the fungal bracket that "mandated emergency treatment; most likely felling of the tree" before the tree failed is the 2-yearly one. Hence, when finding for the Claimant in the 'Final summary and result' of the Judgment, in para 71 the Judge says;

"(ix) that a two-yearly inspection would have discovered that the tree was diseased well in advance of the accident; (x) that the tree would have been felled or otherwise made safe and the accident would not have occurred;"

Painful lessons

What lessons can we learn from the Cavanagh Judgment so far? For one, the key evidence that was presented to the court is completely at odds with basic arboricultural knowledge, and the court relies on the evidence of its experts. There are three major problems.

1. The presence of a fungal bracket at or near the base of a tree is most emphatically not a sure sign of impending failure. It's an obvious tree risk feature that's inviting a closer look, and to carry out a more detailed assessment.
2. Counting the layers of pore tubes, like the candles on a birthday cake, to age a fungal bracket is flawed, and they're not all born in autumn. The focus on ageing the fungal bracket to justify the inspection frequency of 3 years, but not contest the significance of its presence was an own goal. It left the Judge in a position where the only sensible decision was to go for the inspection frequency that meant the fungal bracket could be found before the tree failed.
3. 'Begging the question' evidence that conflates high-use with high-risk, and large tree with high-risk, is not helpful to the court when it has to make a tough decision about reasonable, proportionate, and reasonably practicable tree risk management.

The logical end-game: 3 Inspections per year

At this point, you might have a niggling sense of something not being quite right. A feeling of disquiet you can't quite put your finger on. If so, it's probably this. If a fungal bracket really 'is a sure sign of impending failure', then how come the tree didn't fall in late summer of 2009, when it's claimed the fungal bracket first appeared? Or whenever it first appeared? If a fungal bracket really 'is a sure sign of impending failure', then equally surely, don't you then need to find it as soon as it appears, and not wait up to 2 years for the next inspection? What that'd mean is at the end of every autumn, end of every spring, and end of every summer, the duty holder would need to pay for high-risk trees next to high-risk roads to be inspected to check whether there's a fungal bracket present.

Back to the future

Stretching over 10 years, from Poll to Cavanagh, there remains a terrible gulf between reasonable, proportionate, and reasonably practicable tree risk assessment and management, and expert evidence in the court. Yet, between 2006 - 2016 there'd been considerable evolution in our understanding of tree risk from the likes of the NTSG and the RRAC. Both were the most relevant sources of tree risk management guidance in January 2012, and up to the 2016 court trial, yet neither the NTSG nor the RRAC are mentioned in the Judgment. This omission is noteworthy because in the NTSG's, 'How this guidance could be applied', at 'Scenario 4: Local authority - rural', the inspection frequency suggested is every 3 years in high-use zones.

Before the accident and the court trial, we already knew from research commissioned by the NTSG that compared to other everyday risks we readily accept, the overall risk to us from tree failure is extremely low. The annual risk of death or serious injury from tree failure is less than one in a million. We also knew,

"…the prospects of reducing the risk (from falling trees) below the current level are remote and comparable to finding a microscopic needle in a gargantuan haystack."

Public Safety and Risk Assessment (2011), Professor David Ball, Centre for Decision Analysis and Risk Management

In a third Cavanagh-related article, I'll look at tree risk-benefit management strategies in this context, tree risk-benefit assessment (not inspection) frequencies, and the overarching importance of a Policy. We'll also explore whether the Cavanagh Lime could've been a "microscopic needle".

Note: This article is based on the contents of the Cavanagh Judgment. In order to get a better understanding of the evidence and thinking behind the expert's decisions recorded in the Judgment, I made a request for the expert witness reports and joint statement to be disclosed. First, with DWF, who defended Witley Parish Council. And second, with Witley Parish Council under the Freedom of Information Environmental Information Regulations 2004. On both occasions, my request for disclosure of the expert reports was refused. Finally, I applied to the Queen's Bench Division, and have been told by the court that the expert witness reports are not in the public domain.

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