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Re: BS:5837 20% offset question

Subject: Re: BS:5837 20% offset question
From: alison parish
Date: Jan 20 2008 18:25:25 
______________________________________________________________________
Freelance Arborists required by Landscaping Company to undertake tree
surveys to BS 5837.

Please e-mail expressions of interest to mark@xxxxxxxxxxxxxxx.co.uk together
with information relating to geographic coverage offered.
______________________________________________________________________

Ian
For the purpose of BS5837 I take 'open grown' to mean a tree whose root
system is not compromised by the presence of structures e.g buildings, roads
etc within the nominal circular RPA.
I dont think the BS intended to mean a tree growing in isloation from other
trees because neighbouring trees can have overlapping root systems, each
individual root exploiting different soil layers.
Apologies for the use of non technical terms but if I did use technical
terms I dare say those more exact than myself would start a debate un the
use of those terms (also I'm not in the office and dont have reference to
that excellen diagram explaining this)
When discussing the offsetting of the RPA with a Mathematician he calculated
that:
(assuming all parts of the root system were equally important to the tree
for nutrient and moisture uptake; and a limiting factor for the efficiency
of the root system was the distance of the root tip to the trunk)
1. For a tree in the centre of a circular area offsetting by 20% would only
amount to a reduction in 1% in the growth unit of the original i.e the
ability to absorb water and nutruents
2. If the RPA was square and the tree offset by 20% in the direction one of
the sides the reduction would be less than 1% of the original ability to
absorb nutrients
3. As 2 above but if offset along the diagnals to one of the right angles
the offset would also be less than 1%.
If his findings sparks a debate Ill willingly try and explain his maths
further! 
Regards
Alison
---- Original Message -----
From: "ian cupper" <iancupper@xxxxxx.com> 
To: "UK Tree Care" <uktc@xxxxxx.tree-care.info>
Sent: Saturday, January 19, 2008 11:38 AM
Subject: BS:5837 20% offset question



______________________________________________________________________
Freelance Arborists required by Landscaping Company to undertake tree
surveys to BS 5837.
Please e-mail expressions of interest to mark@xxxxxxxxxxxxxxx.co.uk
together 
with information relating to geographic coverage offered.
______________________________________________________________________
An RPA can be represented on a TCP plan as a circle, a
polygon or a square. The fundamental shape is
determined by the existing trees root morphology.

A 20% offset can be applied on open grown trees, and
this effectively allows the RPA to be moved depending
on the tree's species and the current site conditions.

The RPA cannot be reduced.

If this is the case, what's is the difference between
using a polygon rather than a circle to achieve the
desired RPA?

Thanks for your comments, Ian.

PS. What does open grown mean exactly? is this 'open'
to interpretation? Or does there have to be cohesion
between canopies etc?





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