Tree Protection
Core concepts
Protection begins before equipment arrives. Define a Tree Protection Zone from trunk diameter - a common minimum is 30 cm (1 ft) of radius per 2.5 cm (1 in) of DBH, extended for sensitive or high-value trees - and fence it on day one. The critical root zone describes where roots actually are, usually well beyond the drip line. Protect soil as much as trunks: compaction, fill, and grade changes kill roots, and a single pass of heavy equipment can raise bulk density past recovery without remediation. Specifications should cover fencing, signage, material storage, washout locations, and monitoring. Use air excavation to locate roots before trenching; tunnel or bore rather than cut; prune roots cleanly where unavoidable.
Traps
- Using the drip line as the root zone - it badly underestimates root spread.
- Installing fence after demolition starts; the damage happens in the first days.
- Ignoring grade changes and fill, which suffocate roots without direct injury.
- Treating mulch piles, material storage, and washout as harmless.
- Allowing 'temporary' traffic inside the TPZ during rain or a rush.
Worked example
A 40 cm DBH oak: minimum protective radius ≈ 16 m if using 1 ft per inch of DBH (about 40 ft), and more if the tree is retained as a specimen. Fence that radius, exclude storage, and route utilities by bore rather than trench.
Rule of thumb
One inch of trunk diameter equals one foot of protective radius as a minimum - and when in doubt, double it.