UKTC Archive

Re: Diameter callipers

Subject: Re: Diameter callipers
From: Bill Anderson
Date: Aug 16 2019 10:53:18
One wag (possibly Chris Hastie) pointed out that BS5837 2005 quoted Matheny
and Clark for the 12 times rule, which quoted BS5837 1991 for the source of
the rule Wayne. This is useful when explaining to Planning Officers that
the RPA can't ever be "exact...."

On Fri, 16 Aug 2019 at 11:20, Simon Pryce Arboriculture <
info@xxxxxxxxxxx.co.uk> wrote:

There is some science in previous BS5837 distances was the table in the
1980 version with shorter distances for conifers, reflecting that
conifer root systems are inherently more compact and the 1991 version
which factored in age and vigour.

Jim's too diplomatic to say the the 12x figure was pulled out of the air
- it works because most (NOT all) roots are closer than that in most
cases.  The words often overlooked in the 5837 2005 and 2012 are that
the RPA should be an "_area equivalent__to_" a circle.  In open ground a
circle might be a reasonably accurate reflection of where the root
actually are, but not many development sites round here are large and
open.  Just drawing 12x radius circles round every tree is fine
geometry, but doesn't need any arb expertise. However it is hard to get
out of the habit of drawing circles and straight lines - those Helix
geometry sets we had at school didn't help.

Simon





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