Approved Documents · OPW11/0335

Matrix Projects (QLD)- Essence of Peregian, David Low Way Peregian Beach QLD 4573 Page 10

 

4.2

If there is cause for concern and further details are required for a full
assessment then the use of diagnostic tools such as Resistograph ®, Picus®,
increment borers, soil excavation for root assessment, and Fractometer®
testing are used. From either the initial visual assessment or the use of
diagnostic tools, failure criteria may be given for each tree assessed, and an
informed decision is reached for recommendations.

VTA may be used to state to what extent a defective tree is at greater risk of
breaking or failure, compared with a completely sound one. In QTRA this is
shown as the PoF or in retention value this may result in a lower value.

Tree Protection Methods and Roots

Tree protection involves the minimising of damage to the tree’s root and
vascular system during activities such as construction or installation of root
barriers, thus reducing the chance of tree health decline or death, and the
possible damage to the structural stability of the tree from root damage.
Failure to maintain a minimum tree protection zone may result in declining
long term vigour, health and structural stability in a tree on a construction site.
All trees to be retained on a construction site should have protected root zones
that are measured off the DBH of the trunk via either the Matheny & Clark
(Harris 2004, & Matheny & Clark 1998) formula, the British Standards (BS
5837:2005) for protecting trees, or the newly released Australian Standards
(AS 4970-2009 Protection of Trees on Development Sites).

Using the Matheny & Clarks method a previous understanding of a tree
species tolerance to disturbance (good, moderate, or poor) is required to work
out the Tree Protection Zone (TPZ). This distance calculation is simplified
under BS 5837:2005 where a trunk diameter (DBH) times 12 is used, the same
for AS 4970-2009. Therefore for this report and management of the tree
protection during development, the measurement of TPZ is taken from AS
4970-2009 to calculate impacts and their effects on the trees.

In relation to the majority of trees across the site, where fill will be greater
than 300mm the retention of trees becomes impossible. Assessment of the
bulk earthworks plan indicates that fill will surround all trees, not just one side
or part of their required TPZ. Generally fill over tree roots results in reduced
aeration of the root zone, therefore leading to root death or dieback, and finally
in most instances tree death.

Although instances of fill near Melaleuca quinquenervia have been found to
have a minimal effect on the tree species under the right situations (personal
observations), given the overall age, poor health, and structural condition of
the Melaleuca’s on the site and the extensive nature and depth of filling across
the site, the result would be tree death and or increased whole tree failures in
the future.

 

Leaf and Limb Horticultural ConsultancyO
Prepared by Samuel Cowie 11% of June 2009