Can excavation occur within a tree protection zone?
Excavation can sometimes occur within a tree protection zone, but you cannot assume that it is permitted simply because the tree itself is not being removed.
Excavation can damage roots or disturb the soil needed to keep the tree healthy. For a protected tree, the Urban Forest Act controls activities within its protection zone, including excavation and root damage.
For example, excavation may become prohibited groundwork where it:
- damages the tree’s root system; or
- excavates soil beyond the thresholds specified by the Urban Forest Act.
Where the proposed works involve prohibited groundwork, the appropriate approval must be obtained before undertaking the work. A Tree Management Plan (TMP) may also be required to demonstrate how the tree will be protected during construction. The current Tree Management Plan Guidelines remain in force.
Reference: Urban Forest Act 2023 – s 15, Meaning of prohibited groundwork – Urban Forest Act 2023 | HTML view
Short Answer
Yes, but excavation within the tree protection zone of a protected tree may require approval and must be carefully managed. Under the Urban Forest Act 2023, certain excavation within a protected tree's protection zone is specifically treated as prohibited groundwork
Detailed Explanation
The key provision is the Urban Forest Act 2023, s 15 – Meaning of prohibited groundwork.
For a protected tree, prohibited groundwork within its protection zone includes activities such as:
- damaging the tree's root system;
- compacting the soil in at least 10% of the protection zone;
- excavating to a depth greater than 100 mm over an area of 4 m² or larger, other than cultivation for horticultural purposes; and
- raising the soil level by more than 100 mm over an area of 4 m² or larger, subject to the stated horticultural exception.
Importantly, these thresholds should not be interpreted as giving an automatic right to excavate below them. For example, excavation that directly damages the protected tree's root system can itself constitute prohibited groundwork irrespective of whether the 100 mm/4 m² excavation threshold is reached.
Where an activity would or may damage a protected tree or constitute prohibited groundwork, the Urban Forest Act approval process applies. The Urban Forest (Tree Management Plans) Guidelines 2025 (No 1) (NI2025-364) are the current guidelines governing the preparation of TMPs and remain in force as at September 2026.
Example: If excavation for the foundations of a proposed dwelling extends into the protection zone of a protected tree, an arboricultural assessment may be needed to determine the impact on the root system and appropriate construction/protection measures. The excavation should not simply proceed on the assumption that being outside the tree trunk or canopy makes it acceptable.
No minimum block size does not remove the need for planning assessment.
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