After a storm, a damaged tree can look deceptively stable while hiding serious structural problems beneath the surface. Knowing what to look for can help you make a quick safety call — but a thorough assessment should always be carried out by a qualified arborist. Here's what to check and what the warning signs mean.
Stay Safe Before You Approach
Before getting close to any storm-affected tree, take a moment to assess from a distance. Never approach a tree that is leaning against power lines — treat it as live and dangerous, and contact your lines company immediately. WorkSafe NZ recommends keeping a safe distance from any unstable structure until it has been assessed by a professional. Also watch for hanging branches (sometimes called widow-makers) that could fall without warning.
Signs of Structural Compromise to Look For
1. Visible Lean or Shift
A tree that has developed a new lean since the storm — especially one that wasn't there before — is a major red flag. Compare it to neighbouring trees or structures. A sudden lean often means root failure or trunk damage at or below ground level.
2. Root Disturbance
Check the base of the tree carefully. Look for:
- Soil heaving or mounding on one side of the root zone
- Exposed or snapped roots pulling out of the ground
- Cracks in the soil radiating away from the base
- A gap between the root plate and the surrounding ground
Root failure is one of the most dangerous forms of storm damage because the tree can fall with very little additional warning.
3. Trunk Cracks and Splits
Run your eyes along the full length of the trunk. Look for:
- Longitudinal (vertical) cracks running up the trunk — these can indicate internal splitting
- Co-dominant stems (two main trunks of similar size) that have partially split apart at the union
- Bark torn away in strips, exposing bare wood
- Compression wood — a wrinkled or buckled appearance on one side of the trunk
4. Broken or Hanging Branches
Hanging branches lodged in the canopy are extremely hazardous. They may be held in place by bark or other branches and can fall unpredictably. Even smaller branches can cause serious injury. This is one of the most common post-storm hazards in New Zealand gardens.
5. Canopy Damage and Crown Loss
Large sections of the crown missing or stripped away can dramatically change how wind loads act on the remaining structure. Asymmetric crown loss can cause the tree to become unbalanced and more prone to failure in future wind events.
6. Decay and Cavities
Storms often reveal or worsen pre-existing decay. Look for:
- Hollow sounds when you knock on the trunk (though this requires getting close — only do so when safe)
- Fungal fruiting bodies (mushrooms or conks) at the base or on the trunk — these are a strong indicator of internal decay
- Soft or discoloured wood visible in any cracks or wounds
7. Bark Damage and Wounds
Large areas of stripped or missing bark expose the cambium layer and can compromise the tree's structural integrity and long-term health. Fresh wounds also create entry points for pathogens.
A Quick Reference: Warning Signs at a Glance
| Warning Sign | Risk Level | Action |
|---|---|---|
| New lean with soil heave | Very High | Keep clear, call arborist immediately |
| Hanging branches in canopy | Very High | Keep clear, call arborist immediately |
| Contact with power lines | Extreme | Call lines company first |
| Trunk cracks or splits | High | Do not approach, call arborist |
| Fungal growth at base | Medium–High | Arborist assessment needed |
| Minor branch breakage | Lower | Monitor; arborist can advise |
What Happens Underground Matters Too
Many storm failures begin in the root system, which you can't fully see. Compacted soils, previous construction work near the tree, or root rot from fungal disease can all weaken a tree's anchorage long before a storm hits. An arborist may use tools such as a resistograph or sonic tomograph to assess internal decay and root health — assessments that simply aren't possible with a visual check alone.
NZ Context: Wind Zones and Tree Risk
New Zealand's varied climate means trees in coastal and exposed areas face significantly higher wind loads than those in sheltered urban gardens. BRANZ provides guidance on NZ wind zones, and the NZ Building Code considers wind design in structural assessments. Trees near buildings, driveways, or boundaries carry a higher consequence of failure — meaning even a moderate risk tree in these locations warrants prompt professional attention.
If a tree has fallen and damaged a fence, building, or other structure, you may need to consider whether a building consent is required for any repair work. Check with your local council, or visit MBIE Building Performance for guidance.
When to Call a Professional
You should contact a qualified arborist any time you observe the warning signs above, or if you are simply unsure. Look for an arborist who holds a New Zealand Certificate in Arboriculture or is a member of the New Zealand Arboricultural Association (NZAA). For trees near power lines, your lines company must be involved before any work begins — this is non-negotiable for safety and legal reasons.
Tree removal or significant pruning near structures may also require a resource consent or be subject to notable tree schedules in your district plan — always check with your local council before removing a tree, even a damaged one.
You can find qualified, local arborists on tradedirectory.co.nz to get a professional assessment quickly after storm damage.
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