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A Canadian client has advised that in Canada whilst there are no national standards pertaining to tree protection, there are by-laws in most areas that control TPZ installations. However, they do vary from city to city or even within the same city.

For example the City of Kingston has a TPZ that states :  The TPZ shall be a minimum distance of 1.5 metres beyond the Drip Line of the tree or group of trees, and some trees and some site conditions may require a larger TPZ.

The City of Toronto on the other hand has a TPZ that has a chart and it varies if in an area of city protected by the Ravine and Natural Features by-law:

She has asked ‘What is your formula and are there any options to adjust based upon local by-laws being used’?

Answer: ArborCAD is currently based on Australian standards for calculating the Root Protection and Tree Protection Zones and this is based on measurements taken of the diameter of the trunk at a specific height and using a well thought out formula to generate the circular zone around the trunk….

Structural Root Zone (SRZ): RSRZ = (D x 50)0.42 x 0.64  where RSRZ = Radius of the circle and D = Stem Diameter.

Tree Protection Zone (TPZ): TPZ = DBH x 12 where DBH is the diameter of the tree trunk as measured or calculated by the Arborist at 1.4m above ground

In order to make the software specific to any region outside Australia we simply need to know the formula being used in that region. As far as we have been able to ascertain, Australia may be the only place on earth that has a standard™ for this calculation but it is likely this standard could be adopted for use anywhere. Alternatively we could write changes into the software to suit different regions regulations.

P.S. We have been made aware by Mr David Gunter, Technical Officer for Queensland Arboricultural Association (Australia) that the Australian Standards for tree protection on development sites are based on the British Standard BS-5837.

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