RFI - Attachment 3 - Arborcultural Impact Assessment Report · 132003.221108.3

STRUCTURE                   Reference to the structural integrity of the tree with consideration of the
                            crown, trunk and roots. Determined using the Visual Tree Assessment
                            (VTA) method (Matheck and Breloer 1994). The failure of small (<60mm
                            calliper) live or dead limbs is normal and not considered here.
Very poor:                  Clear indications that a significant failure is likely in the near future
Poor:                       Signs of structural weakness obvious and failure likely, one might expect a
                            significant failure event within the next 5 years, possibly tomorrow
Fair:                       Signs of weakness present though not obviously significant, likely to
                            become worse over time
Good:                       No obvious signs of structural weakness
TREE NUMBER                 Identifying number allocated to individual trees or groups of trees, used to
                            locate trees using site plans or tags on trees.
TREE PROTECTION             An exclusion / protection area measured at ground level nominally circular
ZONE (TPZ)                  with the trunk at its centre, expressed by its radius in metres.
                            The TPZ allows for protection of canopy and roots; both the structural roots
                            that give the tree stability and the smaller absorption roots. The radius of the
                            TPZ is normally calculated for each tree by multiplying the DBH × 12. The
                            minimum distance will be 2m and maximum 15 as stipulated in the
                            Australian Standard 4970-2009 – Protection of trees on development sites.
REFERENCE                   Unique identifier assigned to an individual report by the Author
ULE                         Useful Life Expectancy is an estimation of how many years a tree can
                            reasonably be retained in the landscape provided growing conditions do not
                            significantly worsen and any recommended works are completed. It takes
                            into consideration factors such as risk, species, age, health and site
                            conditions.



8 QTRA Method
The Quantified Tree Risk Assessment (QTRA) system, developed by Mike Ellison at Cheshire
Woodlands, applies established and accepted risk management principles to tree safety
management. The system moves the management of tree safety away from labelling trees as either
‘safe’ or ‘unsafe’ and thereby away from requiring definitive judgements from either tree assessors
or tree managers. Instead, QTRA quantifies the risk of significant harm from tree failure in a way
that enables tree managers to balance safety with tree values and operate to predetermined limits of
tolerable or acceptable risk.

By quantifying the risk from tree failure as a probability, QTRA enables a tree owner or manager to
manage the risk in accordance with widely applied and internationally recognised levels of risk
tolerance. QTRA further provides a decision-making framework which considers the balance
between the benefits provided by trees, levels of risk they pose, and costs of risk management.
Using QTRA, the land-use (Target) upon which trees could fail is assessed first. By valuing the
Target first, the tree owner and the risk assessor are able to determine whether or not, and to what
degree of rigour, a survey or inspection of the trees is required. Where necessary, the tree is then
evaluated in terms of its size and probability of failure. Ranges of value for Target, Size, and
Probability of Failure are entered into a QTRA calculator which generates a traffic light colour-

    Tree Report: (AIA-27 Bayview NH-120226)                             Report Number:     (001)

    Prepared by (Sam Carr – Specialist Arbor Services Pty Ltd)                          Page 13 of 26