08/1787 - Response to Information Request [As Published] · 132008.1787

Seahaven Development Pty Lid- 9-19 Hastings Street Noosa QLD 4567 11]

 

 

42 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 zoncs
that are measured off the DBH of the trunk via the Matheny & Clark (Harris
2004, & Matheny & Clark 1998) formula or the use of the British Standards
(BS 5837:2005) for protecting trees, with knowledge of the critical root zone
which takes into account structural stability issues.

Using the Matheny & Clarks method a previous understanding of a tree
species tolerance to disturbance (good, moderate, or poor) is required. For
example, the Callitris columellaris is a tree of moderate tolerance and would
require a 5.22 metre radius protection zone for Tree No 28 (smaller of the two
on site). This distance calculation is the same as BS 5837:2005. Assessment
of the impacts indicates that nothing near this could be achieved.

Under BS 5837-1991 this radial distance could be reduced by 1/3 for 120
degrees of the total circle, but under BS 5837:2005 an offset of the distance up
to 20% in one direction maybe undertaken on open grown trees. Given that
the trees are already in situations where root distribution has been modified by
surrounding structures, this highly unlikely to be achicvable.

The final method of critical root zone is used to calculate the bare minimum
protection zone required to stop damage to the major woody roots and
structural root ‘formations that maintain tree stability. Critical root zone is
based on the triink DBH times by 5; thus giving a minimum of 2.18 metres.
Given that even this minimum distance will be hard to maintain, even all
around cach of the five trees, therefore long term health and structural
instability will result for all five trees.

43 Design Concepts to Support Trees
The establishment of trees on a site must take into account the requirements
for tree growth, that being adequate soi! volume to allow root growth and
spread, adequate above ground space to allow canopy spread, water
penctration into the root zone, and sufficient space around.the trunk to allow
expansion of the trunk base flare. This will be influence further by the specics
of tree, its canopy habit, and eventual size.

4.3.1 Make Space for Roots
Roots support the tree and soil is the primary source of nutrients for tree
growth, therefore adequate soil volume must be made to support root growth
and distribution. In the situation with the Hastings Strect frontage of the site,
adequate soil volume must be provided for tree growth ifa reasonable
oulcome is required. Image No 1 (Urban 2008, page 295, figure 2.6.3) shows
the outcomes from limited soil volumes on iree growth and longevity.

 

Leaf and Limb Horticuftural Consultancy
Prepared by Samuel Cowie 29" of January 2009

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