UKTC Archive

Re: Tree Risk Communication

Subject: Re: Tree Risk Communication
From: Wayne Tyson
Date: Aug 01 2020 22:09:20
Here in the US we once had a car. A lot of people were burned alive (or
dead, depending upon the context) in them because of a faulty design, but
not quite enough to make a recall statistically "sensible." It would cost
more than paying the wrongful death claims. Simple, eh? Pay the wrongful
death claims. After all, a corporation's first duty is to its stockholders.


On Sat, Aug 1, 2020 at 9:00 AM Bill Anderson <> wrote:

Excellent podcast David, thanks for the link.

On Fri, 31 Jul 2020 at 16:51, Rupert Baker <>

Succinctly put, Jim;  something I often wonder about.
Given that we must all regularly come across trees which show signs of
failure; and recommend works to reduce the probability of such failure,
assumes that the stock of trees with appreciable levels of target is -
gradually - having those most prone to sudden failure removed, it'd be
to think that we were making a difference;
But as we all know, the risk is lower than for many things us humans get
up to; and lower than many uninvited risks we are exposed to
Have a good weekend!

-----Original Message-----
From: On Behalf Of Jim Quaife
Sent: 31 July 2020 13:24
To: UK Tree Care <>
Subject: RE: Tree Risk Communication

The problem with facts is that individuals choose to ignore them if their
opinions/concerns are challenged. (Witness C-19!).
The incredibly low number of tree-associated deaths (of members of the
public) does make the statistics insignificant.  This is on two counts.
One is that the sample numbers are so small that one cannot draw from
any trends whatsoever; and two, in the science of statistics, for
statistics to be significant the element of randomness has to be removed,
or at least reduced to a miniscule degree.
Whatever comfort we derive professionally from surveying trees for risk,
the harsh reality is that serious tree incidents are entirely random.
many this is counter-intuitive because, hey, surely our surveys prevent
incidents?   They might, but we have absolutely no idea, and the pressing
question is - would there be any more tree incidents if no tree surveys
were carried out?  One suspects the answer must be yes, but there is no
proof, nor any means of providing it.
Tree surveys provide a fallacious peace of mind, but they are ingrained
the psyche of tree managers and demanded by insurers.
Personally I find court decisions which conclude that a tree manager has
no credible tree risk management policy and that contributed to the cause
of the incident to be little more that "gut feeling".  (That is not to
that the decision of a court for the manager to instigate or improve tree
surveys is not right in the context of the victim or more especially the
relatives in cases of fatality.) The bottom line is that I cannot, and do
not suggest that tree risk surveys are not carried out.  Scientifically
would be impossible to justify, but our behaviour is most certainly not
scientific to the extent that the behaviour of any given individual is
reliably predictable in the presence of a tree.
This is an intractable dilemma, but the progress made in the mindset of
conducting tree surveys (almost invariably the product of the opinion of
individual) in recent years will, if more generally adopted (and in this
respect one must look at the more established methods with a critical
will improve the situation.
Right, this brings me to lunch - I'm off.

-----Original Message-----
From: [mailto:] On Behalf Of Jerry Ross
Sent: 31 July 2020 12:36
To: UK Tree Care
Subject: Re: Tree Risk Communication

David, Chris got there some years ago with this:

Chris Hastie, arboriculturist and webmaster of the The UK Tree Care
Mailing List recently got fed up with the assumptions that are made about
such things. He writes:

"After the storms the other month I was phoned by a journalist who
questioned me about various things, mostly to do with a very large horse
chestnut by the side of a busy road which managed to blow over and do no
harm to anything except a lamp post. Trying to explain the nuances of
management to her and knowing everything I said was going to be massively
dumbed down, I started to wish I had a few soundbites at my fingertips.

So Chris took the question at face value and worked out some statistics.
He started by pointing out that the chances of being killed by a tree in
public space in the UK is about 1 in 20,000,000 (according to the UK
& Safety Executive, “Management of the risk from falling trees – Internal
guidance”). So, what about winning the lottery jackpot?
Actually, Chris also demonstrated that rather than the 14 million to one
which is usually quoted, the chances of winning it are actually better
expressed as 1 in 268,920. This is because although the chances of
with one ticket are indeed 1 in 13,983,816, accidental deaths are usually
expressed as the chances of any incident happening to any person in one
year. So, assuming a lottery player buys one ticket per week every week
a year, the odds are reduced to 1 in 268,920. Thus a regular lottery
is 75 times more likely to win the lottery jackpot than be killed by a
in a public space.
He goes on with some other sobering illustrations. The total number of
accidental deaths in the UK is over 12,000 per year. About 6 of these are
due to trees. So you are 2000 times more likely to die from some other
of accident than by being hit by a falling tree. More specifically, 3,501
people were killed in road traffic accidents in the UK in 2005. So you
around 600 times more likely to be killed in a road accident than by a
falling tree. The Ranger adds one of his own – the annual risk of being
struck (and not necessarily killed) by lightning is 1 in 10,000,000. So
are more likely to be hit by a bolt of lightning than killed by a falling
tree. That seems to put things into perspective. Anyone else want to
have a
try? Cite your sources if you do!

Taken from
Nick Hellis has similarly relevant statistics on his website (or had - I
can't locate it now but his website is here

The most up to date research shows that between January 1999 and January
2009 there were 64 fatalities in the UK resulting from trees or parts of
trees failing an average of 6.4 fatalities per year.

Accidents at work account for 144 fatalities a year and accidents at home
account for 3,380 fatalities a year. In other words, you are 50 times
likely to be fatally injured at home than you are to be fatally injured
a tree.

*Non-Fatal injuries caused by Trees*

The number of A&E cases in the UK attributable to being struck by trees
parts of trees is around 55 a year out of a total of some 2.9 million
annual leisure-related A&E cases.

Footballs account for 262,000 cases per year; Children’s swings account
for 10,900 per year and Wheelie bins account for 2,200 cases per year.

*Risk of Fatal Injury caused by Trees*

The annual risk to any one individual of being killed by a tree is
1:10,000,000 (i.e. 6 deaths per 60 million head of population)

The HSE state that people regard a risk of ‘one death in a million’ as
insignificant or trivial in their ‘daily or normal life’.

The individual risk of death caused by trees is one tenth or ten times
lower than the risk people accept as being insignificant or trivial in
their ‘daily or normal life’.

*Fatalities in ‘normal or daily life’*

The following table compares the calculated risks that are experienced in
‘daily or normal life’.

*Causes of death *

*Annual risk *

*Annual number of fatalities*

Accidents at home, all ages (1)

1 in 17,000


Road traffic accidents (2)

1 in 37,000


Murder (3)

1 in 91,000


Accidents at work (4)

1 in 458,000


Insignificant or trivial risk (HSE definition)

1 in 1,000,000


Trees (5)

1 in 10,000,000


Lightning (6)

1 in 33,000,000



(1)Office for National Statistics Mortality Statistics – Injury and

(2)Department for Transport Road Casualties Great Britain: 2013

(3)Year ending March 2018 – Office for National Statistics

(4)Health and Safety Executive – Fatal Injuries in Great Britain 2017/18

(5)Centre for Decision Analysis and Risk Management

(6)Lightning deaths in the United Kingdom: a 30-year analysis…. D. M.

However, as Michael suggests, I doubt if knowing all this would stop
people asking to have trees taken down 'because they might blow down'.

On 31/07/2020 10:41, David Evans wrote:
Those of you who have to explain tree risk to civilians might find
this useful.

You're at greater risk from going on a 200 miles round trip in a car
to visit friends for a weekend than from branches or trees falling
over a whole

I think this is such a relatable comparative risk that everyone
accepts without thought, and usually involves driving past trees, I'm
using it in the next version of VALID's Tree Risk-Benefit Management
Strategies that I'm working on.

*A micromort is a one in a million chance of death

The risk from a 200 miles road trip = 1 micromort

The annual risk from trees = less than 1 micromort

For those of you who are interested in this kind of stuff.  The 200
miles statistic is from Tim Harford's marvellous 'Cautionary Tales -
The Spreadsheet of Life and Death', available here.

It's about why the Value of Statistical Life is so important.  The
tragic tale of Clive Stone is a neat illustration of the folly of not
using a VSOL, and a great skewering of populist politics.  Concerning
trees, it explains why the costs of tree risk assessment and
management are a crucial part of the risk equation.  And why the, 'If
it saves one life' argument is an empty one.


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The UK Tree Care mailing list
To unsubscribe send

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits

The UK Tree Care mailing list
To unsubscribe send

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits

The UK Tree Care mailing list
To unsubscribe send

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits