Recognising Tree Risk: A Visual Guide for NSW Owners

Tree failure is rarely a surprise

Most NSW tree failures that hurt someone or damage property show warning signs in the months or years before they fail. The signs are usually visible to a property owner who knows what to look for. They are easier to spot in winter (no foliage hiding the structure) and after storms (when stressed wood reveals itself).

This post walks through the seven categories of visible risk indicators we look at during TRAQ assessments. None of these on their own says "remove the tree tomorrow", but recognising them is the first step in deciding whether to engage a qualified arborist for a proper Tree Risk Assessment.

1. Visible cracks in trunk or major branches

Cracks fall into three categories:

• Hairline (surface only): common, generally low concern. Often associated with rapid growth.
• Clear visible cracks but stable: moderate concern. Watch for any change between inspections.
• Deep, opening, extending into the wood: high concern. These can indicate failure in progress. Engage a TRAQ arborist immediately.

Cracks at branch junctions (especially Y-shaped junctions with included bark) are higher risk than mid-branch cracks. After any storm, walk the tree and check for new cracks.

2. Decay – cavities, soft wood, woodpecker holes

Some decay is normal in mature trees and doesn't indicate failure risk. The questions to ask:

• Where is the decay? Small cavities in dead branches: not concerning. Decay in the main trunk or at major branch junctions: more concerning.
• How much remaining sound wood? Trees can typically tolerate decay up to about 30% of the cross-section before structural failure becomes likely.
• What's adjacent to the decay? Decay extending into a stress-loaded area (under a leaning trunk, at a major branch attachment) is higher concern.

A consulting arborist may use a resistograph (a small drill) or sounding mallet to assess decay depth and extent quantitatively. Visible decay surface is only part of the picture.

3. Deadwood in the canopy

All trees have some deadwood. The question is how much, how big, and where:

• Small twigs and minor deadwood (under 50 mm): normal, low concern unless over a target.
• Significant deadwood (50 mm+ branches): moderate concern, particularly over occupied targets.
• Major dead limbs (large structural branches dead, overhead): high concern. Particularly hazardous if the deadwood is over a play area, driveway, building or busy thoroughfare.

Deadwooding is normal arboricultural maintenance and falls in the AS 4373 recognised practices. For trees over occupied targets, an annual deadwood inspection is reasonable practice.

4. Lean

Not all lean is bad. Three patterns:

• Natural lean the tree has always had: usually low concern. The tree has adapted its root system and wood to the lean.
• New lean (developed in recent months/years, accompanied by soil cracking on the upper side or exposed roots on the lower side): high concern. This is root-plate failure in progress.
• Severe lean (over 20 degrees): elevated concern regardless of history, particularly if over a target.

Storms can transition a stable natural lean to an unstable new lean by failing the root plate. After any major weather event, inspect leaning trees specifically.

5. Canopy / foliage condition

Compare the current canopy to what the species should look like in good health:

• Full and healthy: low concern.
• Some thinning but most healthy: low-moderate concern, watch for trend.
• Significant dieback: moderate-high concern, indicates stress.
• Mostly or entirely dead canopy: high concern – the tree is at or near end of life regardless of how stable the trunk looks today.

Sudden canopy dieback after construction often indicates soil-related damage discussed in our Soil and Trees post.

6. Fungal fruiting bodies on live tissue

Mushrooms or brackets on dead wood or nearby stumps are normal. Fungal fruiting bodies growing on the live trunk or root flare are one of the strongest predictors of internal decay and elevated future-failure risk. Common in NSW:

• Ganoderma brackets (large, shelf-like, often near the base): root and butt rot
• Honey fungus (Armillaria) at the base: serious root disease
• Inonotus species on trunks: heart rot in mature eucalypts

If you see fungal brackets growing from the live wood of a mature tree, particularly with a target underneath, engage a TRAQ-qualified arborist promptly.

7. Recent root-zone disturbance

Any soil disturbance within the Tree Protection Zone in the past 2-3 years can have affected the root system in ways that show up later. Common triggers:

• Driveway or paving installation
• Service trenching (water, gas, electrical)
• Soil-level change (fill against trunk, excavation exposing roots)
• Vehicle traffic or materials storage causing compaction
• Removal of an adjacent tree (changes wind exposure and microclimate for the remaining tree)

Trees that look fine in year 1 post-disturbance often decline in years 2-4. Worth a TRAQ baseline inspection at the time of disturbance with follow-up monitoring.

Frequently asked questions