Every removal decision is a judgement call. Old trees are valuable, they take decades to replace, they shade, shelter and store carbon, and they're worth several thousand dollars apiece in property value terms. So no arborist worth the name recommends a removal without a reason. Here are the nine clearest reasons we recommend removal on New Zealand properties.
1. Hollow trunk with thin walls
Trees with hollow trunks can stand for decades, many native pohutukawa and totara are largely hollow at the base. What matters is the wall thickness: the ratio of solid wood to total trunk diameter. A common rule of thumb is that if the remaining sound wood is less than about 30% of the trunk's radius, the tree's structural margin is gone. Knock the trunk with a hammer or rubber mallet, dead, drum-like notes are a red flag. Resistance drilling can confirm it.
2. Major fungal fruiting bodies on the trunk or base
Bracket fungi (Ganoderma, Phellinus, honey fungus / Armillaria) fruiting at the base or up the trunk usually mean the heartwood inside is already significantly decayed. Mushrooms on a tree are not a tree problem, they're the visible symptom of an internal problem that's been going for years.
3. Lifting root plate
Walk around the base. If you can see soil cracking, mounding or lifting on one side, particularly the side opposite a lean, the root plate is starting to fail. This is one of the most serious signs you'll see and means the tree could come down in the next strong wind. It's especially common after wet winters.
4. Sudden lean
Trees that have always leaned aren't necessarily a problem, they've grown reaction wood to support the lean. A new lean, particularly one that's appeared after a storm or wet weather, is different. It usually means the roots have shifted. We treat sudden lean as a high-priority assessment.
5. Major dieback in the upper canopy
Lots of dead branches in the top third of the tree (when the rest of the canopy is still green) signals the tree is losing the ability to push water and nutrients to its highest points. The cause might be root damage, drought stress, pathogen, or just old age. If more than about a third of the upper canopy is dead and there's no sign of recovery after a season, the tree is on the way out.
6. Splits, cracks or seam cracks
Vertical seam cracks on the trunk, especially long ones, ones that have been there for years, or ones with weeping sap or dieback above them, often indicate internal decay. Y-form forks with included bark (where bark is pinched between the two trunks rather than properly joined) are also high-risk: those forks let go without warning.
7. Storm damage that's left it compromised
A tree that has lost a major limb or had its crown ripped open often can't recover its form. The remaining structure may now be unbalanced, the wound surface may invite decay, and what's left often becomes more dangerous in the next storm. Sometimes a heavy crown reduction can save it; often, removal is the safer call.
8. The wrong species in the wrong place
Some species simply outgrow residential sites. Eucalypts (gums) over kids' play areas have a habit of dropping limbs without warning. Willows and poplars sent into soakage trenches and sewer lines are an ongoing maintenance bill. Macrocarpa next to houses become a fire risk in dry summers. If the tree can't be safely managed long-term in its current position, removal-and-replant is often the best long-term call.
9. Construction damage to the root system
Trees that have had major excavation, trenching or compaction within their root zone often don't show the damage for 2–5 years. By the time the canopy starts thinning and dying back, the tree has been losing roots for some time. Where root damage exceeds about 30% of the root zone, the tree's long-term prospects are poor.
What about a tree that's "just messy"?
Leaf litter, sap drops, blossoming bird mess, fruit drops onto cars, these aren't reasons to remove a healthy tree, in our view. They're the cost of living with a mature tree, and most can be reduced with pruning rather than removal.
The same goes for a tree that's "too tall" or "blocking the view." A reduction prune to the right standard can usually solve the view issue without sacrificing the tree.
Council consent, quick reminder
Even with all nine signs above, you may need council consent before removing a tree. Notable Trees, trees in heritage areas, large native trees in significant ecological areas, they're protected by District Plan rules regardless of condition. See our piece on when you need council consent for tree work.