The No.1 Reason Trees Fail

Including

IMPORTANT FACTORS

TREE
HEALTH

Tree health describes a tree’s overall condition, including its strength, vitality, and ability to cope with stress and recover from damage.

If a trees health is in decline, it will affect the trees load capability.

TREE
STRUCTURE

This is how the tree is built mechanically. This should be seperate from tree health as a tree may have fantastic vigour but fail because of mechanical strees.

If a tree has poor structure, it will affect the trees load capability.

ROOT
PLATE

The primary anchor of a tree. Often shallow in the ground and widespread.

If a trees root plate is comprimised, it will affect the trees load capability.

ENVIRONMENTAL FACTORS

Environmental factors are everything around the tree. This may include nearby buildings, other trees, compacted soil, recent construction works, rain, wind etc.

If the tree has poor environmental factors, it will affect the trees load capability.

WHY TREES FAIL (LOAD CAPACITY)

Load capacity is critical in managing tree risk because it determines how much force a tree or branch can safely withstand before it fails.

Trees are constantly subjected to forces such as wind, gravity, and the weight of their own canopy. A tree will only fail when those forces exceed the strength of the wood, roots, or branch attachments. In other words, the NO.1 REASON TREES FAIL is because...

LOAD > LOAD CAPACITY.

Understanding load capacity helps arborists identify weak points in a tree, such as decayed wood, poor branch unions, long heavy limbs, or compromised root systems. These factors reduce the tree’s ability to resist forces acting upon it.

Managing tree risk therefore involves either increasing load capacity or reducing the load placed on the tree. In practice, increasing load capacity is often difficult because it depends on biological factors like wood strength and root health. Cable systems can be used in certain scenarios to increase load capcity but should only be done so under professional recommendation/installation.

EXAMPLE RISKY TREE SCENARIOS

Tree Health

Decay in the trunk
A large pruning wound allows decay fungi to colonise the trunk, reducing the strength of the wood. This significantly lowers the trunk’s load capacity, meaning normal wind forces may now cause failure.

Dead branch wood
A large limb dies and the wood begins to dry and crack. Dead wood is more brittle, which reduces its ability to flex and absorb loads, increasing the likelihood of breakage.

Tree Structure

Co-dominant stems with included bark
Two stems grow from the same point with bark trapped between them. This weak attachment reduces the load capacity of the union, making it more likely to split under wind loading.

Long overextended limb
A branch grows long with heavy weight toward the tip. The increased leverage greatly increases bending stress, meaning the branch reaches its load capacity much sooner.

Roots

Root severance during construction
Excavation cuts several major structural roots near the trunk. With fewer roots anchoring the tree, the load capacity of the root plate is reduced, increasing the chance of uprooting in storms.

Root decay
Fungal decay weakens large structural roots below ground. As the roots lose strength, the tree’s anchorage capacity declines, making it more vulnerable to windthrow.

Environmental Factors

Severe windstorm
A strong storm dramatically increases the force acting on the canopy. The load increases rapidly, which may exceed the tree’s load capacity and cause failure.

Saturated soil after heavy rain
Waterlogged soil loses strength and grip around the roots. This reduces the load capacity of the root system, making uprooting more likely even in moderate wind.

the mop and bucket

Imagine holding a mop horizontally with a bucket of water hanging off the end.

The mop handle represents the branch.
The bucket of water represents the foliage mass and branch weight at the tips.
Your hand/shoulder represents the branch union or trunk attachment point.

Even if the bucket isn’t extremely heavy, the farther it is from your body, the harder it becomes to hold because of leverage.

The force increases due to the length of the lever arm.

You can reduce the strain in two ways:

Reduce the weight in the bucket
→ selective foliage/end weight reduction
Shorten the mop handle
→ reduction pruning back to suitable laterals

That’s essentially what we do biomechanically:

reduce bending moments
reduce lever arm length
reduce sail area and dynamic loading
redistribute weight closer to the trunk

If you hold:

a 10kg bucket close to your chest → manageable
the same 10kg bucket at arm’s length → exhausting

The weight didn’t change.
The leverage did.

Trees experience exactly the same mechanical principles in:

wind loading
horizontal limbs
end-weighted scaffold branches
codominant stems
overextended laterals

HOW COUNCILS ASSESS PERMITS

Most councils assess tree permit applications using a mix of:

planning controls
arboricultural principles
risk management
neighbourhood character
environmental value
amenity impacts

The exact process varies between councils, but across Victoria the assessment framework is usually fairly similar.

Typical council assessment process

1. Is the tree protected?

Council first checks whether the tree is covered by:

Vegetation Protection Overlay (VPO)
Significant Landscape Overlay (SLO)
Environmental Significance Overlay (ESO)
Heritage Overlay
local tree preservation laws
native vegetation controls
planning permit triggers

They also look at:

trunk diameter (DBH)
species
location on the property
whether it’s native or indigenous
proximity to waterways or bushfire zones

If the tree isn’t protected, a permit may not even be required.

2. Arboricultural value assessment

Council often assesses the tree similarly to how an arborist would.

Typical considerations include:

Health & condition

vitality
decay
pest/disease issues
structural integrity
expected useful life expectancy (ULE)

Structure

codominant stems
included bark
cavities
deadwood
overextended limbs
previous poor pruning

Species significance

indigenous/native value
habitat contribution
rarity
canopy contribution

Size & maturity

Large mature trees receive much stronger protection because:

canopy takes decades to replace
environmental value compounds with age
urban cooling benefits are significant

3. Risk assessment

Councils heavily weigh:

likelihood of failure
likelihood of impact
consequences of failure

Many councils informally follow principles from:

TRAQ
QTRA
THREATS
general arboricultural risk frameworks

But they also distinguish between:

manageable risk
vs
unacceptable risk

A tree having “some risk” is usually not enough for removal approval.

They often expect:

pruning
target management
monitoring
bracing
before approving removal.

4. Amenity vs inconvenience

This is where many applications fail.

Councils usually separate:

Valid arboricultural reasons from Lifestyle inconvenience.

Common reasons councils often reject:

leaf drop
blocked gutters
shade
roots in lawn
bird mess
minor cracking
fear of trees
solar panel shading
general maintenance burden

Common reasons more likely to succeed:

verified structural failure risk
irreversible decline
major infrastructure damage
building impact
severe pathogen issues
poor species suitability
irreversible root conflict
significant safety defects

5. Proposed pruning specification

For pruning applications, councils look at:

pruning percentage
pruning type
AS 4373 compliance
long-term effects
whether natural form is retained

Heavy canopy reductions are commonly rejected if they:

disfigure the tree
induce decline
create future hazard potential

Councils often prefer:

selective reduction
deadwooding
structural pruning
end weight reduction
rather than blanket canopy thinning.

6. Replacement planting

If removal is approved, councils frequently require:

replacement trees
minimum pot sizes
indigenous/native species
canopy targets
offsets

Some councils are now strongly focused on:

urban heat reduction
canopy cover targets
biodiversity corridors

especially around metropolitan Melbourne.

What helps an application succeed?

Strong arborist reports

The best reports:

quantify defects
explain biomechanics
include targets and likelihood
reference standards
use photos clearly
propose reasonable alternatives

Councils respond much better to:

objective evidence
than emotional arguments.

Councils also consider politics/community pressure

In reality:

neighbour objections matter
large visible trees get more scrutiny
streetscape value influences outcomes
officer discretion plays a huge role

A healthy prominent canopy tree often receives very high protection even if defects exist.

The strongest applications usually:

acknowledge tree value honestly
demonstrate defects clearly
show proportional management
avoid exaggerated danger claims
propose staged or conservative pruning first

Applications that say:

“Tree is dangerous and may fall”

without evidence often get rejected quickly.

Whereas:

“Overextended lateral over target area with progressive end-weight loading, historic included bark failure indicators, and limited retrenchment potential”

is much more persuasive because it demonstrates biomechanical reasoning rather than fear.