UKTC Archive

RE: Tree Risk Communication

Subject: RE: Tree Risk Communication
From: Rupert Baker
Date: Jul 31 2020 15:51:27
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, one 
assumes that the stock of trees with appreciable levels of target is - 
gradually - having those most prone to sudden failure removed, it'd be nice 
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 them 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.  For 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 in 
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 say 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 it 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 an 
individual) in recent years will, if more generally adopted (and in this 
respect one must look at the more established methods with a critical eye), 
will improve the situation.
Right, this brings me to lunch - I'm off.

-----Original Message-----
[] 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 risk 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 a 
public space in the UK is about 1 in 20,000,000 (according to the UK Health & 
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 winning 
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 for a year, 
the odds are reduced to 1 in 268,920. Thus a regular lottery player is 75 
times more likely to win the lottery jackpot than be killed by a tree 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 type 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 are 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 you 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 more 
likely to be fatally injured at home than you are to be fatally injured by a 

*Non-Fatal injuries caused by Trees*

The number of A&E cases in the UK attributable to being struck by trees or 
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 poisoning

(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. Elsom

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 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