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Tree Protection Zone Calculator

What is a Tree Protection Zone (TPZ)?

The Tree Protection Zone of a tree is a distance from the stem set aside for the protection of a tree’s crown and roots to provide for the viability and stability of the tree. It is an estimate of the area required to protect a tree from adverse construction impacts. No construction activity or changes to soil levels should occur within this area. Because a tree’s crown and roots do not always grow in a perfect circle around the stem, it is a hypothetical estimation of the area to be protected. The actual location of tree roots can only be determined by carrying out root investigation via excavation by a qualified arborist. The Tree Protection Zone is a minimum area set aside for protection of a tree.

When does the Tree Protection Zone need to be calculated?

You must calculate the Tree Protection Zone of a tree:

  • before you alter soil levels (eg. by excavation or fill) close to a tree to find out if the works are within the Tree Protection Zone. If they are then you must obtain a Tree Permit for the works before you start.
  • before you submit a development application to find out if if any development is proposed within the Tree Protection Zone of any:
    • tree on land upon which development is proposed,
    • tree on adjoining land, or
    • street tree.

How to calculate a Tree Protection Zone - step by step

Step 1: Measure the Circumference of the Tree Stem (trunk)

Measuring the circumference of a tree trunk
Trees with only one stem (trunk)
  • Measure the circumference of the tree stem
  • The circumference of a tree stem is the length around it.
  • The circumference can be calculated by wrapping a flexible tape measure around the stem tightly.
  • The tape should be wrapped around the stem at 1.4 metres above ground level.

Trees with more than one stem (trunk)

  • Measure the circumference of each tree stem
  • The circumference of a tree stem is the length around it.
  • The circumference can be calculated by wrapping a flexible tape measure around the stem tightly.
  • The tape should be wrapped around the stem at 1.4 metres above ground level.
Measuring more than one trunk

Step 2: Calculate the TPZ

  • Put all your circumference measurements (from Step 1) into the TPZ Calculator.
  • The Calculator will give you the TPZ distance. This distance is a radius from the trunk of the tree.

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Step 3: Measure the TPZ distance on the ground

The TPZ of a tree is measured by laying a tape measure on the ground and measuring the TPZ distance (calculated in Step 2) radially from the stem to form a circle around the tree stem. This circle is the TPZ.

Measuring the TPZ distance on the ground

Palm, Cycads and Tree Ferns

You do not need to calculate the TPZ of palms, cycads and tree ferns. For these plants, the TPZ should not be less than 1 metre outside the crown.

Calculating the TPZ of palms Measuring the TPZ of palms, cycads and tree ferns


Last updated on 28 July 2016