Hi Tim,
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.
I'll await a correction form BS on their expensive new edition..............
Have a good weekend
Rupert
-----Original Message-----
From: Tim Moya [mailto:Tim.Moya@xxxxxxxxxxxxxxxx.co.uk]
Sent: 24 May 2012 22:30
To: UK Tree Care
Subject: RE: BS5837-2012 - Combined Stem Diameter
I think Paul has a point
My maths is not as good as it once was but it seems to me that there are
some scenarios where the BS formula for more than 5 stems will give a result
that makes no sense.
If you have a tree with one stem of 400mm and 4 stems of 100mm the first
calculation will give a root protection radius (RPR) which represents the
combined cross sectional area of the stem
If you add another stem of 100mm to the same tree and use calculation 2 you
get an RPR of about 80% of the smaller tree
The resulting root protection area for calculation 2 will be about 65% of
the smaller tree's RPA
If you increase the size of the larger stem to 600mm the result is that the
RPA for calculation 2 is about half of that for calculation 1 (even though
it's a bigger tree)
For both the examples of calculation 2 above you would get a larger RPA by
taking the largest stem and treating the tree as single stemmed - although
this can't be the answer either.
One possibility would be to simply use the largest 5 stems and calculation 1
where there is a one large and several small stems. It would give a better
result
While not getting hung up on the maths is fair enough, the calculation in
the BS surely has to work as a reliable guide.
TIM MOYA
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