Dear Jim
I know. I'm not hung up on the maths and I am completely aware that the RPA
is a monumental guess!
But one has to consider the potential for being challenged if one calculates
and presents a RPA and this is lower than a strict application of the
formulae in BS5837:2012. If one uses the >5 (mean stem diameter) formula for
a tree with 2-5 stems and the variation in stem diameters is large, then the
combined diameter and the resulting RPA can be significantly lower. I wonder
whether this would be justifiable on the basis of survey efficiency / speed
(e.g. sycamore regeneration with 5 stems between 100mm and 150mm - is it
worth taking 5 measurements or is estimating an average and using the mean
stem formula appropriate?).
In terms of crown mass - are you suggesting we just amend RPAs regardless of
the measured diameters? I understand why you might consider that, but what
rules might you apply? (I know that you are going to say - use your
experience and deep understanding of tree root systems and morphology!)
Paul Muir
Arboricultural Consultant / Contracts Administrator
Treework Environmental Practice, The Old Rectory, Pilgrims Way, Chew Stoke,
BS40 8TT
M: 07966 647906
T: 0117 244 0012 (Head Office)
www.treeworks.co.uk
Treework Environmental Practice has moved and developed our regional
presence! Please see the new Head Office address and telephone number above
with local representatives now based in the Midlands (0121 647 7021) and the
Southeast (0207 871 3003).
Treework Environmental Practice is the trading name of Treework Services Ltd.
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-----Original Message-----
From: Jim Quaife [mailto:jq@xxxxxxxxxxxxxxxxx.co.uk]
Sent: 24 May 2012 08:44
To: UK Tree Care
Subject: RE: BS5837-2012 - Combined Stem Diameter
Hi Paul,
Don't get to hung up on at arithmetic - these are trees! With multiple stems
by all means measure to estimate an equivalent single stem diameter, but use
your judgement in respect of crown mass and all the other site circumstances
to determine an RPA.
Jim
-----Original Message-----
From: Paul Muir [mailto:PaulMuir@xxxxxxxxxx.co.uk]
Sent: 23 May 2012 19:02
To: UK Tree Care
Subject: BS5837-2012 - Combined Stem Diameter
We had a meeting this week to determine how we will introduce changes to our
tree management / survey database to conform to BS5837:2012.
Has anyone else noticed that the two formula proposed for calculating the
combined stem diameter of multi-stemmed trees (sections 4.6.1a and
4.6.1b) are not mathematically equivalent? The formula for trees with more
than 5 stems generates a smaller combined diameter (where stems are not equal
in diameter). While I am not too concerned about the implications for the
actual areas generated in terms of protection of the root zone, I wonder if
this was intentional, and if so what the logic was - other than for sensible
data collection.
As an example, if one actually measured the diameters of each stem of a hazel
stool with 10 stems, then inputted these into the 2-5 stems formula this does
not generate the same combined diameter as if one entered the average stem
diameter of these measured stems into the >5 stems formula. As the 2-5 stem
formula is based on the formula for calculating the equivalent area of a
"virtual" single stemmed tree with the intention of representing the
multi-stemmed tree, I wonder what the
5 stems formula is based on.
Depending on the diameters used the differences are significant and are of
course exaggerated when calculating a corresponding RPA.
We only noticed this when we explored the potential for allowing a short-cut
when surveying, involving recording one average stem diameter for trees with
2-5 stems, where the trees were insignificant or perhaps where the stems are
of very similar (and small) magnitudes.
Not a very interesting issue, I know, but...
Paul Muir
Arboricultural Consultant / Contracts Administrator
Treework Environmental Practice, The Old Rectory, Pilgrims Way, Chew Stoke,
BS40 8TT
M: 07966 647906
T: 0117 244 0012 (Head Office)
www.treeworks.co.uk <http://www.treeworks.co.uk/>
Treework Environmental Practice has moved and developed our regional
presence! Please see the new Head Office address and telephone number above
with local representatives now based in the Midlands (0121 647
7021) and the Southeast (0207 871 3003).
Treework Environmental Practice is the trading name of Treework Services Ltd.
Registered Office & Place of registration: Treework Services Ltd, The Old
Rectory, Chew Stoke, Bristol, BS40 8TT
Reg No.: 1621606
VAT No.: 397 4028 23
This email including attachments is intended for the addressed recipient
only. It may contain confidential information and may be subject to legal,
professional or other privilege. It must not be copied, disclosed or used by
any other person. If you are not the intended recipient, please notify the
sender and then delete from your system immediately.
Treework Environmental Practice does not guarantee the attachments or
enclosures are secure or virus-free.
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