UKTC Archive

FW: Highway Rooting constraint and pollard street trees - assessing and plotting a rational RPA

Subject: FW: Highway Rooting constraint and pollard street trees - assessing and plotting a rational RPA
From: Andy Clout
Date: Sep 12 2019 16:26:10
Evening all,

I had a scan through the archive as I recalled that there was a former 
discussion on interpretation/plotting of the BS5837 RPA in the pollarded 
street tree scenario.  I was interested to see that it was in 2010 and 
referred to the fact that the 2005 edition stated that the area of RPA may 
change shape dependent on recognised existing rooting constraints, but 
"should not be reduced in area".

In 2012 the revised version removed this stipulation. I assume that this was 
in response to some experienced arb's involved in the process recognising 
that in areas of significant existing constraint or (perhaps) where trees 
have been or are being managed in a reduced form, they may be expected to 
have a reduced minimum area/volume of rooting medium required to sustain 
them.  The caveat that RPA "modification should reflect a soundly based 
arboricultural assessment of likely root distribution" was introduced.

Every year I get consulted on lots of developments with associated AIA's. I 
would estimate less than 10% are ever based on an RPA shape that is not 
circular, seemingly regardless of existing site conditions/rooting 
constraints.

Two Q's arise in terms of issues that I am currently encountering:

Can we as an industry agree a consensus on how much of a constraint on 
rooting a standard adopted highway authority construction spec.  road imposes 
on the plotting of a rational RPA for a roadside tree?

My view is that whether it be inclusion in the next revised BS or an AA/ICF 
recognised approach, a minimum off-set would be a good starting point. 25%?

Can we as an industry agree on some form of standardised approach to 
assessing by how much the standard RPA of a mature pollarded tree can be 
reduced by from the norm?

My view is that this is a more difficult generalisation however, if managed 
crown form is X% of what would be considered average for species, size and 
position an allied % reduction in RPA from the norm would seem to be a 
reasonable approach. Clearly where the pollard is immediately adjacent to an 
engineered highway the RPA is going to be off-set away from the road in any 
event - isn't it?

I appreciate that there will be those who feel each individual scenario 
requires a specific approach. However, I believe that as an industry we need 
to find improved consistency in our approach to making such judgements that 
can be more easily understood by those working in allied development related 
industries and those ultimately charged with judging how "soundly based" the 
arboriculturist's assessment is when they disagree with another 
arboriculturist in this respect.

Regards

Andy

Andy Clout
Landscape and Tree Officer
Planning Services
Waverley Borough Council
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