UKTC Archive

RE: Statistical Risk vs Ecosystem Services - does this compute?

Subject: RE: Statistical Risk vs Ecosystem Services - does this compute?
From: Jim Quaife
Date: Dec 04 2019 12:00:41
Hi Chris,
The problem with tree risk statistics is that in the science of stats they 
are not significant - I didn't know this but I have been educated by someone 
who does.
I thought that statistical significance was to do with the sample size, but 
it is not. Significance is determined by the absence of randomness.  This is 
not always possible and so stats which contain randomness have to be adjusted 
to compensate, and that usually means that the reliance one can put upon them 
decreases proportionately.
The problem with tree incidents is that they are random.
We like think that our tree surveys are comprehensive and professional (which 
they are - hopefully) but accurate prediction of tree failures is virtually 
unheard of.  We specify work that requires attention where we can anticipate 
failure, but we have absolutely no idea whether in so doing we have actually 
prevented an incident.  Intuitively we think we have of course and I do not 
question the integrity of surveyors (myself included!), but there is no way 
we can prove it.
Regretfully it follows that any calculations based on a random data are of 
questionable worth in actuality.   Interesting yes, but applicable?
We all love numbers as they provide reassurance (particularly to insurers who 
hover over all this), but I would be very wary of basing any sort of policy 
or programme on such calculations.
Although it may sound "woolly", tree risk assessments are justifiable because 
the alternative of not conducting them is not.
Jim  

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info 
[mailto:uktc-request@xxxxxx.tree-care.info] On Behalf Of Corder, Chris
Sent: 04 December 2019 11:43
To: UK Tree Care
Subject: Statistical Risk vs Ecosystem Services - does this compute? 

Dear all, 

I am a sad case. I only have numbers to comfort me.
So I was wondering where the risk-benefit of trees might lie.
Maybe someone has already done this?
If not, does the following compute?

For arguments sake...lets agree that the background of risk of death in 
'public spaces' in the UK seems to be in the order of 1/10,000,000
Lets also assume/agree that the Value of Statistical Life is £2M
6 deaths per year = value of risk of £12M per year
“A value of statistical life of £1,000,000 is just another way of saying that 
a reduction in risk of death of 1/100,000 per year has a value of £10 per 
year” (HSE, 1996)"
Therefore, divide £12M by 1/10,000,000 = risk value of £1.20
The i-Tree Eco London study found that 8,421,000 trees provided £132,700,000 
per year of ecosystem services i.e. £15 per tree per year (or near as damn 
it). So lets assume £15 per tree might be about right.
£15 eco value per tree/£1.20 risk value = 12.5
So...is it right to say that the background risk from trees would need to be 
12.5 times greater before the ecosystem benefits start to become outweighed?
If so, then presumably the background risk from trees could increase to 
somewhere in the region of 1/800,000 before the risk starts to outweigh 
ecosystem benefits?
(Which is sort of where the Tolerable/Broadly Acceptable region of the ToR 
Framework lies...is this coincidence?) 

Does this compute or have I gone start raving mad?

p.s. I get the daily digest...so I won't see any replies in real time. So 
thanks in advance. And sorry in advance for delay in reply. 

All the best, 
Chris 

Christopher Corder PDArb (RFS), BSc (Hons) in arboriculture, MArborA
Assistant Arboricultural Manager
Hampshire Highways 
Tel: 0300 XXX XXXX
Web: www.hants.gov.uk/roads
@Hantshighways

© Hampshire County Council 2017 | Disclaimer | Privacy Statement

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of Alastair Durkin
Sent: 03 December 2019 08:56
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: RE: Replacement trees in an area TPO

Hi Jon the situation is this:

If you have an area TPO and allow a tree to be removed, subject to 
replacement planting then you MUST either make a new TPO on the replacement 
OR formally 'vary' the TPO to include the new individual tree. Otherwise the 
tree is not protected. 

The 'C' business is for giving effect to planning conditions under s197, it's 
not for TPO app conditions. See section 4 of the model order. 

Hope this helps.

Alastair


-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of Jon Heuch
Sent: 01 December 2019 14:14
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Replacement trees in an area TPO

Good folk of uktc

 

Remind me what should happen if the removal of a protected tree covered by an 
area order is allowed, but a condition is given to plant a replacement tree? 
The order may or may not contain separate individual protected trees.

 

The order can't be altered to include an individual tree shown within the 
protected area, can it?

 

The tree officer who gave permission will remember but what is there on 
record to show a protected replacement tree? The replacement tree will 
clearly be younger than the order, so not seemingly protected to subsequent 
tree officers.

 

Do area orders get conditional replacement trees? Do they get Tree 
Replacement Notices?

 

Is this just a failing of the Area order?

 

Jon

 

 




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