root protection area help

[jim11]

I am having trouble working out the rpa, is there a simple way other than bs5837 way because im sure when i studied it at college we measured the stem diameter in mm and x by 12 but then i cant remember what we did with the end result to get it into metres. Any help would be greatl recieved- maths is not my strong point as you might gather. Thanks

[Paul Barton]

Take the stem diameter in mm. Multiply by 12. Divide by 1000 (to convert mm in to metres). You now have the radius (half the diameter) of a circular RPA.

 

If you want to work out the area of the RPA in square metres, take the radius figure and square it (multiply it by it's own value) then multiply by 3.142 (Pi).

[PhilBeech]

What he said...^^^

[toprotter]

Do you not x by 10 on single stem and x 12 on twin stemmed trees ?

Might be completely wrong and it wouldn't be the first time ;-)

[Paul Barton]

Good point toprotter.

 

It's 12 x on single stems and 10 x on multi-stemmed trees (measured at just above the root flare).

 

Remember, these are the recommendations of the BS - not golden rules. You get some pretty wacky RPAs on coppice stools!

[Paul Barton]

Good point toprotter.

 

It's 12 x on single stems and 10 x on multi-stemmed trees (measured at just above the root flare).

 

Remember, these are the recommendations of the BS - not golden rules. You get some pretty wacky RPAs on coppice stools!

[j r hartly]

Stool:-)

[Nimby]

I have a supe xcel document that does this for you. Email me and I will send it to you.

[AA Teccie (Paul)]

Not sure how acceptable it would be but you could simply say the RPA is 12m radius (based on a tree with a diameter of 1.0m, i.e. 12x 1.0m = 12m radius), perhaps too simplistic but avoids the calculation to find the area.

 

The trouble here is that the RPA is often not a circle and hence application of the 'area', to best fit the particular situtaion, is where you as the expert come in.

 

Lastly NJUG 10 (superceded by V.4 I beleive) used to talk about the dripline, i.e. edge of the crown, OR 4 times tree girth, whichever is the greatest, as the root protection zone. Never far out in my expereince.

 

Cheers..

Paul

[ScottF]

I generally use the 12x stem diameter "halo" around trees in the first instance. You really need to have a good reason for drastically offsetting an RPA away from the default circle (such as a fixed barrier, like a wall or building, a limiting factor like an abrupt change in soil type or a slope). That's not to say that roots don't offset, because they do, but unless you're Airspading to determine the root area, I think it's best to keep your offset assumptions conservative.

 

I've seen the area vs circle approach used fairly disingenuously to wildly alter and greatly limit radial RPAs by unscrupulous arbs to squeeze buildings in between trees on development sites. I don't think this is in the spirit of the standard, and should be constrained by the 20% maximum offset (for individual trees) in any event.