What Causes Tree Trunks to Split or Crack?

A cracked tree trunk can be more serious than it looks.

Tree trunks are designed to carry enormous weight, support large canopies, and withstand wind, rain, heat, and seasonal growth. So when a trunk starts to split or crack, it is usually a sign that something is placing stress on the tree.

Some cracks are minor and can be monitored. Others can point to internal decay, storm damage, poor structure, or a serious safety risk. The challenge for most homeowners is knowing which is which.

At Harvey Tree Care, we help property owners across Harvey, Yarloop, Benger, Brunswick, Waroona, Burekup and surrounding areas assess cracked, split, and storm-damaged trees. Here’s what causes tree trunks to split, when you should be concerned, and when tree pruning or tree removal may be needed.

Why Tree Trunks Split

Tree trunks can split for several reasons. Sometimes it happens suddenly after a storm. Other times, the crack develops slowly over months or years.

Common causes include:

• Storm stress
• Strong winds
• Heavy branch weight
• Heat and sun exposure
• Internal decay
• Fungal disease
• Poor branch structure
• Old pruning wounds
• Sudden changes in moisture
• Root instability

A visible crack should never be ignored, especially if the tree is close to a home, shed, fence, driveway, road, or outdoor area.

Storms and Strong Winds

Storms are one of the most common reasons tree trunks split or crack. Strong winds place pressure on the trunk, branches, and root system. If the tree already has a weak point, the force of the wind can cause the trunk to open up.

This is especially common when a tree has:

• A heavy canopy
• Multiple main trunks
• Dead or weak limbs
• Uneven branch weight
• Internal decay
• Poor past pruning

After a major storm, it is worth checking larger trees for new cracks, splitting branches, or changes in lean. If you notice fresh damage, call qualified arborists for an assessment.

Heat Stress and Sudden Temperature Changes

WA summers can be harsh on trees. Long periods of heat, dry soil, and sudden temperature changes can cause stress in the trunk.

In some trees, the outer bark and inner wood expand and contract at different rates. This can lead to cracking, especially on exposed trunks that receive strong afternoon sun.

Heat-related cracks may appear as:

• Long vertical splits
• Bark lifting or peeling
• Dry, exposed timber
• Cracks on the sun-facing side of the trunk

While not every heat crack means the tree needs to be removed, it can create an entry point for pests, disease, and decay.

Internal Decay

A tree can look healthy on the outside while the inside is slowly breaking down. Internal decay weakens the trunk from within, making it less able to support the weight of the canopy.

Signs of decay may include:

• Fungal growth near the base
• Hollow sounds when the trunk is tapped
• Soft or crumbly wood
• Cavities or holes in the trunk
• Insect activity
• Bark falling away
• Cracks widening over time

A split trunk with internal decay is a serious concern. In many cases, tree removals are recommended when the structure can no longer be made safe.

Poor Branch Structure

Some trees develop weak unions where large branches or trunks meet. This is common in trees with co-dominant stems, where two main trunks grow closely together from the same point.

These unions can trap bark between the stems, preventing strong wood from forming. Over time, the pressure between the two trunks can cause splitting.

Warning signs include:

• A V-shaped fork in the trunk
• Cracking where two stems meet
• One side of the tree pulling away
• Heavy limbs growing in opposite directions
• Previous branch failure in the same area

Professional tree pruning can sometimes reduce the weight on these weak points. But if the split is severe, removal may be the safest option.

Heavy Canopies and Unbalanced Growth

A thick, heavy canopy places extra load on the trunk. If one side of the tree is heavier than the other, the trunk may twist or split under pressure.

This can happen when trees are not pruned properly or when they grow towards light, away from buildings, or over open spaces.

Tree pruning can help by:

• Reducing weight on heavy limbs
• Improving canopy balance
• Removing deadwood
• Increasing airflow
• Reducing storm pressure

Proper pruning should always be selective. Rough tree lopping can make the problem worse by creating weak regrowth and unbalanced structure.

Old Pruning Wounds

Old cuts can become weak points in the trunk or major branches. If a branch was removed incorrectly, the tree may not have sealed the wound properly. This allows water, pests, and decay to enter.

Over time, the damaged area can weaken and split.

This is one reason professional pruning matters. Arborists understand where to cut, how much to remove, and how to protect the tree’s natural healing process.

Root Problems Can Contribute to Cracking

Trunk cracks are not always caused by problems above ground. Root issues can also create structural stress.

If roots are damaged, decaying, or shifting in wet soil, the tree may start to lean or move. This movement can put pressure on the trunk and cause cracks to form.

Root-related warning signs include:

• Soil lifting around the base
• Exposed or damaged roots
• New leaning after rain
• Cracks in the soil
• Fungal growth near roots
• Movement during wind

If root failure is involved, urgent assessment is important. A tree with both root instability and trunk splitting can become dangerous quickly.

When Is a Split Trunk Dangerous?

A split trunk becomes more serious when the crack affects the tree’s main support structure.

You should call an arborist if:

• The crack is deep or widening
• The trunk has split into two sections
• The tree is leaning
• Large branches sit above the crack
• There is decay or fungus present
• The tree is near buildings or people
• The split appeared after a storm
• You can see movement in the crack during wind

If the tree is close to a home, shed, driveway, fence, powerline, or public area, do not wait to have it inspected.

Can a Cracked Tree Be Saved?

Sometimes, yes. It depends on the severity of the split, the tree species, its location, and the overall health of the tree.

A tree may be managed with pruning if:

• The crack is minor
• The tree is otherwise healthy
• The canopy weight can be reduced
• There is no major internal decay
• The tree is not leaning dangerously

Tree removal may be needed if:

• The trunk is splitting apart
• The tree is dead or decaying
• The crack affects the main stem
• The tree is unstable
• The risk to people or property is too high

At Harvey Tree Care, we always assess the tree properly before recommending removal. If pruning can safely manage the risk, we will explain that option. If removal is safer, we will explain why.

Why You Should Not Ignore a Split Trunk

A cracked trunk rarely improves on its own. Even if the tree stays standing for a while, the split can worsen during the next storm, heatwave, or period of heavy rain.

Ignoring a split trunk can lead to:

• Sudden branch failure
• Full tree collapse
• Roof or fence damage
• Blocked driveways or access tracks
• Injury risk
• More expensive emergency removal later

Early action gives you more control and often reduces the cost and complexity of the job.

Frequently Asked Questions

Is a vertical crack in a tree trunk dangerous?
It can be. Some vertical cracks are surface-level, while others indicate serious structural weakness. A professional inspection is recommended.

Can tree pruning fix a split trunk?
Pruning may reduce weight and lower risk, but it cannot repair a serious split. If the trunk is unstable, removal may be required.

Should I remove a tree with a cracked trunk?
Not always. It depends on the depth of the crack, tree health, location, and risk level. An arborist can advise the safest option.

Can heat cause tree trunks to crack?
Yes. Hot WA conditions and sudden temperature changes can contribute to bark and trunk splitting, especially on exposed trees.

Local Arborists for Cracked and Split Trees

If you have noticed a crack or split in a tree trunk, it is worth getting it checked before the problem becomes dangerous. Harvey Tree Care provides professional tree pruning, tree removals, and arborist advice across Harvey, Yarloop, Benger, Brunswick, Waroona, Burekup and surrounding WA areas.

Our experienced arborists can assess the damage, explain your options, and help you decide whether pruning, monitoring, or safe tree removal is the right choice.

Contact Harvey Tree Care today for a free quote and expert advice on cracked, split, or storm-damaged trees.