Attachment 4 - Treee Management Plan_V1

The descriptions of the TPZ and SRZ are taken from the Australian Standards, AS 4970-2009
Protection of trees on development sites. These descriptions only give the basic outline to
calculate the TPZ and SRZ, when encroachment or reduction in the size/area of the TPZ is
required to facilitate the development, these can also be calculated: see Appendix D of the
Australian Standard AS 4970-2009.

8.2.1 TPZ
As specified in the Australian Standard, AS 4970-2009, the Tree Protection Zone (TPZ) is the
principal means of protecting trees on a development site. The TPZ is a calculation that
combines the root area and crown area which require protection and this area should be
isolated from construction disturbance so that the tree can remain in a viable condition for the
future. The TPZ incorporates the Structural Root Zone (SRZ).

The radius of the TPZ is calculated for each tree by multiplying its DBH (Diameter at Breast
Height - trunk diameter measured at 1.4m above ground) by 12.

E.g., a tree with a .5m diameter at 1.4m x 12 results in a 6m Tree Protection Zone (TPZ).

A TPZ should not be less than 2m or greater than 15m (unless crown protection is required).

8.2.2 SRZ
The Structural Root Zone, as specified in AS 4970-2009 the surface area of protection that is
required around a tree to maintain that tree’s stability – a larger area than this is required to
maintain a tree in a viable condition for the future. It is only necessary to calculate the SRZ
when major encroachment into a TPZ is proposed.

An indicative SRZ radius can be determined from the trunk diameter, D, measured in metres
(above the root buttress) and applying the following formula:
                  0.42
RSRZ = (D x 50)          x 0.64

The SRZ for trees with a trunk diameter less than 0.15m will automatically be 1.5m.




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