Approved Plans & Document OPW21-0272

5.    TREE PROTECTION



TREE PROTECTION – AS4970 -2009 ‘Protection of trees on development sites’
The tree protection zone (TPZ) is the principal method of protecting trees on development sites. It is an
area set aside from disturbance from construction works, enabling sufficient parts of a tree and its
growing environment to be undisturbed, so that the tree will remain stable and viable.


Root protection zone (RPZ)
A specified area below ground and at a given distance from the trunk set aside for the protection of tree
roots to provide for the viability and stability of a tree to be retained where it is potentially subject to
damage by development.

NOTE: Establishment of these areas may include root investigation and mapping, root pruning and
installation of root barriers or other protection measures at the edge of the RPZ to prevent conflict
between roots and works.

Structural root zone (SRZ)
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. 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.

Tree
Long lived woody perennial plant greater than (or usually greater than) 3 m in height with one or
relatively few main stems or trunks.

Tree protection zone (TPZ)
The combined area of the root protection zone (RPZ) and crown protection zone (CPZ) as an area set
aside for the protection of a tree.

DETERMINING THE TREE PROTECTION ZONE

Trees should be physically protected at all stages of development. The tree protection zone (TPZ) is
determined by a combination of the areas of primarily the root protection zone (RPZ) and to a lesser
extent, the crown protection zone (CPZ) considering the proposed construction methods and structures.
These zones are illustrated in Figure 1.

The determination of the tree protection zone should involve—

(a) Identifying an area of ground around the tree that should remain undisturbed (root protection zone)
and ensuring that it is feasible to maintain protective measures undisturbed around all such areas
throughout the construction period (see Clause 1.4.6); and

(b) Identifying an area around the tree crown that should remain undisturbed (crown protection zone)
and ensuring that it is feasible to maintain protective measures undisturbed around all such areas
throughout the construction period (see Clause 1.4.1).
The TPZ is plotted to include the RPZ and CPZ.
A site plan showing TPZs should be prepared.

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