Polygon RPA

[daltontrees]

I agree with the point made about volume versus surface area. But I think it is probably a bit of both. But sdince we aren't party to the basis on which the RPA formula was arrived at by BS, we don't know what emphasis has been put on which aspect of root function.

 

For structural roots, the RPA is likely to be more than adequate, and both depth ansd spread are significant factors, depending on species.

 

For water gathering, surface area seems the obvious important factor unless soil depth, texture and structure and topography allow for collection in a dip.

 

For nutrient gathering volume is important but simce many trees are reabsorbing nutrients every year from decayed leaf litter very close to the surface, surface area is also important.

 

For gas exchange, surface area must be by far the most important factor.

 

And as for competition from other trees, shrubs and herbaceous plants?

 

Deviation from a circle and from the 12 x DBH rule should probably be the norm. Someone I work with often expresses RPAs as polygonal CEZs on the basis that things like heras fencing comes in straight lines.

 

My rule is, there is no rule.

[kevinjohnsonmbe]

The standard encourages us to think of roots as occupying areas when they actually occupy volumes.

 

Paul, in your constrained rooting area example I wonder if the trees would still be vertical on a shallow substrate where they couldn't make up their root protection volume by going down?

 

Dunno.

 

Good point Scott, I suppose we should consider the physical volume the roots actually occupy but also the surrounding mass of soil that they draw their nutrients from? Or is that already part of the calculation of the RPA detailed in the table? Or perhaps it's assumed that an RPA whilst drawn as a 2 dimensional representation continues 'downwards' below ground level. Apol's if that 'reads ' a bit rambling, last post before bed and would probably articulate it better if it wasn't late !

[Amelanchier]

Someone I work with often expresses RPAs as polygonal CEZs on the basis that things like heras fencing comes in straight lines.

 

It does, but only in multiples of 3.5m! (plus 75-100mm for connectors)

 

Given the requirement for an accurate dimensionable plan I decided that it was more efficient in the long term for both us, client and LPA to show each and every heras panel (with scaffold or proprietary foot supports), trakpanel and Cellweb unit on our drawings. Its easily done on AutoCad using blocks as shown (the straight line in the attached is a length of post & wire across a low risk area).

Edited January 31, 2014 by Amelanchier

[David Humphries]

I don't have a lot of experience in this field, but it has always struck me as a little odd and counter productive to have the stabilizer poles of barriers the tree side of the CEZ and potentially in the RPA!

 

Obviously having them on the construction side of the barrier would be an obsticle to works.

 

?

 

 

 

.

[Paul Barton]

Someone has gone and parked a car in your fence Tony!

[kevinjohnsonmbe]

I agree with the point made about volume versus surface area. But I think it is probably a bit of both. But sdince we aren't party to the basis on which the RPA formula was arrived at by BS, we don't know what emphasis has been put on which aspect of root function.

 

For structural roots, the RPA is likely to be more than adequate, and both depth ansd spread are significant factors, depending on species.

 

For water gathering, surface area seems the obvious important factor unless soil depth, texture and structure and topography allow for collection in a dip.

 

For nutrient gathering volume is important but simce many trees are reabsorbing nutrients every year from decayed leaf litter very close to the surface, surface area is also important.

 

For gas exchange, surface area must be by far the most important factor.

 

And as for competition from other trees, shrubs and herbaceous plants?

 

Deviation from a circle and from the 12 x DBH rule should probably be the norm. Someone I work with often expresses RPAs as polygonal CEZs on the basis that things like heras fencing comes in straight lines.

 

My rule is, there is no rule.

 

Thank you for your info Jules (esp last line!)

[PhilBeech]

I have been drawing RPA's as polygons for some time now. If you can, as Tony said earlier, annotate to explain clearly your reasoning for this and back that up with site investigation it should be perfectly acceptable by the LPA.

 

Unfortunately there seems to be a great swath of tree officers that won't accept this and want to see circles everywhere. Its a constant battle with domestic 5837 work.

[Amelanchier]

That car had to be removed to enable the development Paul. Facilitation scrappage...

[Gary Prentice]

That car had to be removed to enable the development Paul. Facilitation scrappage...

 

It's normally a JCB on the sites I go on:sneaky2:

[daltontrees]

It does, but only in multiples of 3.5m! (plus 75-100mm for connectors)

 

Given the requirement for an accurate dimensionable plan I decided that it was more efficient in the long term for both us, client and LPA to show each and every heras panel (with scaffold or proprietary foot supports), trakpanel and Cellweb unit on our drawings. Its easily done on AutoCad using blocks as shown (the straight line in the attached is a length of post & wire across a low risk area).

 

Nice illustration! In practice using standard heras panels means the minimum polygon side is 3.5m but they can be overlapped to give straight sections of anything from 3.8m upwards. Standard clips can't be used, but standard tying wire can. I have found guys on site less inclined to remove panels if it nmeans cutting tying wire or having to move a couple of panels.