Dear Richard
One reason to raise this on UKTC is to try to ensure that everyone is aware
of the anomaly that is inherent within the two multi-stemmed formulae within
BS5837:2012 and to emphasise that we should be cautious and fully informed of
the potential outcomes when applying these two formulae.
I do not think it is fair to say that "It is possible in any such averaging
calculation to manipulate the input figures and produce anomalies"
The anomalies arise from a rigid application of the calculations NOT from
manipulating the input figures.
Actually the opposite is true - Manipulating the input figures goes some way
to resolving the issues that arise from directly applying the formulae.
After all we are interested in presenting a consistent RPA appropriate for
the tree in question. Being aware that choosing to measure an extra stem
might reduce the RPA (and reduce it dramatically) is pretty important
wouldn't you agree?
Regards
Paul Muir
Arboricultural Consultant / Contracts Administrator
Treework Environmental Practice, The Old Rectory, Pilgrims Way, Chew Stoke,
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-----Original Message-----
From: Richard Nicholson (Leisure) [mailto:r.nicholson@xxxxxx.gov.uk]
Sent: 28 May 2012 09:03
To: UK Tree Care
Subject: RE: BS5837-2012 - Combined Stem Diameter
<Rupert wrote
I have continued to measure all the stems on a MS tree, added
x-sectional areas, and derived a figure from a notional stem of the same
cross-sectional area, in view of the gremlins in the new proposals.
<Tim added
that would work Rupert - in other words just use the first calculation. Gets
a bit tricky when there are 30 or 50 stems but in that situation they are
often of similar size and the second calculation works better then.
RN
You will recall that in the draft for public consultation there was only one
method, what is now the calculation in 4.6.1 a) The general comment from
arbs. in the form of DPC returns and comments at the AA Reg. Con. meeting was
that its not reasonable to expect an arb to measure every stem. So we added
an average calculation as in 4.6.1 b). It will only give an average, that’s
what averaging gives. It is possible in any such averaging calculation to
manipulate the input figures and produce anomalies, but after all its about
measuring trees not assessing a system against the womping willow or any
other tree which can grow a stem as you look at it.
If Rupert and Tim want to continue to measure every stem, keep calm and carry
on.
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