Approved Document 1 of 3 Arborist Report July 2020 OPW20-0145 · OPW20/0145

Structural Root Zone (SRZ) (AS 4970-2009)
The area around the base of a tree required for the tree’s stability in the ground. The woody root growth and soil cohesion
in this area are necessary to hold the tree upright, so the entire profile (depth) of the root zone is included in the Structural
Root Zone (SRZ). The SRZ is nominally circular with the trunk at its centre and is expressed by its radius in metres.

This zone considers a tree’s structural stability only, not the root zone required for a tree’s vigour and long-term viability,
which will usually be a much larger area.

The SRZ is the critical area required for tree stability and does not consider tree health, which will generally require a much
larger area. While there are many factors that affect the actual size of the SRZ (e.g. tree heights, crown area, soil type, soil
moisture, etc.), the area determined using the trunk diameter provides a general guide indicating where structural roots are
likely to be located. Only thorough root investigation would show the actual location of these roots. Determine SRZ radius
from the trunk diameter (measured immediately above the root buttress) using the following formula or Figure 1.

          SRZ radius = (D x 50)0.42 x 0.64
where
          D = trunk diameter, in metres, measured above the root buttress

Note: The SRZ for trees with trunk diameters less than 0.15 metres will be 1.5 metres.



Figure 1: Structural Root Zone




The curve can be expressed by the following formula:
         RSRZ = (D x 50)0.42 x 0.64


NOTES:
    1.    RSRZ is the Structural Root Zone radius.
    2.    D is the stem diameter measured immediately above root buttress.
    3.    The SRZ for trees less than 0.15 metres diameter shall be 1.5 metres
    4.    The SRZ formula and graph do not apply to palms, other monocots, cycads and tree ferns.
    5.    This does not apply to trees with an asymmetrical root plate.


Source: Australian Standard Protection of Trees on Development Sites AS 4970-2009




Arborist Report for 28 Eenie Creek Road, Noosaville
Prepared by Arbor Operations – July 2020
                                                                                                                  18 | P a g e