Living on Sydney’s North Shore means living alongside some of Australia’s most magnificent trees. From towering Blue Gums to spreading Jacarandas, our leafy canopy is a huge part of what makes this area desirable. But when the winds pick up during a storm, or you notice a large branch hanging precariously over your driveway, admiration can quickly turn to anxiety.
It is a common worry for homeowners: is that large tree in the backyard safe, or is it a ticking time bomb?
The reality is that most trees are structurally sound and can withstand significant weather events. However, trees are living organisms that age, suffer disease, and react to their environment. When structural defects develop, a tree can become a liability. Understanding the difference between a minor issue and a major safety risk is critical for protecting your family and your property.
This guide outlines the specific warning signs of dangerous trees, explains how risk is assessed, and helps you decide when it is time to call a professional arborist.
What Makes a Tree “Dangerous”? (Risk vs Normal Behaviour)
To an untrained eye, a large tree moving in the wind might look terrifying, but flexibility is actually a sign of strength. Trees are designed to sway; it helps them dissipate wind energy. So, what actually constitutes a danger?
In the arboriculture industry, for a tree to be considered “hazardous,” two elements must be present:
- A structural defect that makes failure likely (such as a split trunk or unstable roots).
- A target that would be hit if the tree failed (such as a house, car, powerline, or person).
If a dead tree falls in the middle of an empty paddock, it is part of the natural ecosystem. If that same dead tree stands within striking distance of your verandah or a public footpath, it is a high-priority hazard.
It is also important to distinguish between normal debris and structural failure. Many native Australian trees, particularly Eucalypts, will naturally shed small limbs and bark. This “self-pruning” is normal. However, dropping large, heavy limbs with a diameter greater than 50mm is often a sign of stress or structural weakness that requires attention.
High-Risk Situations on the North Shore
While any tree can develop issues, certain scenarios common to the North Shore increase the urgency of an assessment. The combination of our sloping topography, clay soils, and frequent storms creates specific risks.
You should prioritise a professional inspection if:
- Trees are within striking distance of your home: If a tree is tall enough to hit your roof or main living areas, its structural integrity must be beyond doubt.
- Construction has occurred nearby: Excavation for driveways, pools, or Granny Flats often severs critical roots, destabilising trees years before they show signs of canopy dieback.
- The tree leans toward a boundary or structure: A lean isn’t always bad, but a tree leaning heavily over a neighbour’s fence or your garage needs to be monitored for soil movement.
- Trees are located on retaining walls: Trees growing out of or directly above retaining walls can compromise the wall’s structure, just as a failing wall can destabilise the tree.
- Vegetation is near powerlines: This is a critical safety issue. If a tree is touching or growing into powerlines, do not attempt to prune it yourself. This is a job for certified professionals who work with Ausgrid or Essential Energy protocols.
Warning Signs a Tree May Be Unsafe
Trees rarely fail without giving us clues first. By keeping an eye out for these specific symptoms, you can often catch a problem before it becomes a disaster.
Dead or dropping branches (Deadwood)
Dead wood is dry, brittle, and lacks the flexibility of living timber. It can snap without warning, even on a perfectly calm day—a phenomenon often called “summer limb drop.”
- Look for bare branches when the rest of the tree is leafy.
- Watch for “hangers”—broken branches that have detached but are caught in the canopy, waiting to fall.
- Note if the tree is shedding large limbs rather than just small twigs.
Cracks or splits in the trunk
A crack is a clear sign that the wood fibres are failing under the weight of the tree.
- Vertical cracks: These can indicate internal decay or shearing forces. Two separate stems with a crack between them is a high-failure risk.
- Horizontal cracks: These are less common but extremely dangerous, often indicating the tree is about to snap or uproot.
- Branch unions: Look at where large branches join the trunk. If you see a “V” shape with a crack or bark trapped inside the joint (included bark), that attachment is weak.
Fungal growth or signs of decay
Fungi feeding on a tree often means the wood inside is rotting. While the tree might look green and healthy on the outside, the structural wood holding it up could be turning to mush.
- Look for shelf-like mushrooms (brackets) growing on the trunk or at the base.
- Check for cavities or soft spots in the wood.
- Be wary of trees with large, old pruning wounds that haven’t healed over, as these are entry points for decay.
A sudden lean or soil lifting
Trees naturally grow toward the light, so a gradual lean is often fine. The danger signal is change.
- Root plate movement: Look at the base of the tree on the opposite side of the lean. If the soil is cracked or lifting up (soil heaving), the roots are pulling out of the ground. This is an emergency.
- Sudden lean: If a tree leans significantly after a storm where it stood straight before, it has lost stability.
Hollow areas and termite activity
A hollow tree isn’t automatically dangerous—trees are cylinders, and a tube is structurally strong. However, there is a limit. If the outer shell of sound wood is too thin relative to the height of the tree, it may buckle.
- Look for visible holes or nesting sites that indicate a hollow trunk.
- Check for “mud tubes” on the bark, which indicate termites are active. Termites can rapidly degrade the structural integrity of a tree.
Root damage or disturbed ground
You cannot see the roots, but they are the anchor. If the anchor fails, the ship sinks.
- Has there been trenching for plumbing or NBN recently?
- Is there soil erosion exposing the root plate?
- Have roots been cut to lay paving?
Cutting major roots within the structural root zone significantly increases the risk of the tree toppling during high winds.
Storm Damage: What to Check After Wind and Heavy Rain
Sydney storms can test even the healthiest trees. After a severe weather event, it is vital to perform a visual check of your property from a safe distance.
Start by looking up into the canopy. Are there broken branches hanging loosely? These are immediate hazards. Look at the trunk—has the storm caused any new splits or cracks? Finally, check the ground. Heavy rain softens the soil, reducing the friction that holds roots in place. If the ground around the base of the tree looks disturbed or mounded, the tree may have shifted.
Safety Warning: If a tree has fallen onto powerlines, or is leaning on them, stay at least 8 metres away and call emergency services or the power authority immediately. Do not approach the tree. Similarly, if a large tree is hung up on another tree or a building, do not try to cut it down yourself. This heavy wood is under immense tension and can snap back with lethal force. Call a professional for emergency storm work.
Pruning vs Removal: What’s Often Possible
Spotting a defect doesn’t always mean you have to cut the tree down. In many cases, a qualified arborist can mitigate the risk while keeping the tree.
When Pruning Works:
- Deadwooding: Removing dead branches eliminates the risk of them falling while improving the tree’s health.
- Weight Reduction: Reducing the length of heavy, over-extended branches can reduce the leverage on the trunk and root plate.
- Canopy Thinning: Selectively removing branches allows wind to pass through the tree rather than pushing against it (reducing the “sail effect”).
- Cable Bracing: Installing support cables can provide supplemental support to weak branch unions.
When Removal is Necessary:
- The trunk is severely compromised by rot or cracks.
- The tree has lost stability in the ground (root failure).
- The tree is dead or in irreversible decline.
- The risk to a home or high-traffic area cannot be reduced to an acceptable level through pruning.
For more on maintenance options, see our guide on tree lopping and pruning.
Do You Need Council Approval to Remove a Tree?
On the North Shore, trees are highly valued, and strict regulations protect them. Whether you are in Ku-ring-gai, Hornsby, Willoughby, or North Sydney, there is a high probability that your tree is covered by a Tree Preservation Order (TPO) or Local Environment Plan (LEP).
Generally, you will need approval to remove a tree if it exceeds a certain height (often 5 metres) or trunk diameter. There are exceptions, such as for trees within 3 metres of a foundation (in some council areas) or species listed as exempt weeds.
Crucially, “dangerous” trees often still require evidence. You usually cannot just remove a tree because you think it is dangerous. Councils typically require an arborist’s report confirming the immediate risk before they will grant a permit. Removing a protected tree without approval can result in fines reaching tens of thousands of dollars.
Always check your local council’s specific website or speak to us. We can guide you through the application process and provide the necessary arborist reports.
What Happens During a Professional Tree Risk Assessment?
When you hire a Level 5 Arborist for a risk assessment, they move beyond a simple visual check. They use a systematic approach to evaluate the tree’s structural integrity.
The assessment typically covers:
- Visual Inspection: Checking for the warning signs listed above (decay, cracks, lean).
- Sounding: Using a mallet to listen for changes in tone that indicate hollows.
- Root Inspection: Assessing the soil and root plate stability.
- Target Assessment: Identifying what would be damaged if the tree fell.
- Risk Rating: Assigning a risk level based on the likelihood of failure vs. the consequence of failure.
This professional analysis gives you a definitive answer on whether the tree is safe to keep or needs tree removal.
What Not to Do (Safety Reminders)
If you suspect a tree is dangerous, your behaviour around it should change immediately.
- Do not attempt to climb the tree to inspect the damage.
- Do not use a ladder to remove heavy limbs; ladders are unstable on soft ground, and heavy wood is unpredictable.
- Do not park your car under the tree, especially if storms are forecast.
- Do not ignore the problem hoping it will go away. Structural defects rarely heal themselves; they usually worsen over time.
FAQs
How do I know if a tree is dangerous?
Look for major warning signs: deep cracks in the trunk, soil lifting at the base, fungal brackets (mushrooms) on the wood, or large dead branches. If you see these, book a professional assessment.
Can a healthy-looking tree still be unsafe?
Yes. A tree can have a full green canopy but suffer from significant root rot or internal trunk decay. This is why professional sounding and inspection are important for large trees near homes.
What should I do after a storm damages a tree?
Stay clear of the area. Look for hanging branches or powerline contact from a safe distance. If there is immediate danger to life or property, call the SES or emergency services. For structural assessment and cleanup, contact an arborist.
Can pruning make a tree safer?
Absolutely. Weight reduction pruning reduces the strain on long branches, and thinning the canopy reduces wind load. Removing deadwood eliminates the risk of falling debris.
Do I need council approval to remove a tree on the North Shore?
In most cases, yes. Rules vary by specific council and tree species/size. Even for dead or dangerous trees, you typically need to provide evidence (photos and an arborist report) to the council to avoid fines.
How quickly should I act on dead branches?
If the branches are large (over 50mm diameter) and over a walkway, driveway, or garden, act immediately. They can fall without wind.
What signs suggest root instability?
Mounded or cracked soil on one side of the tree base (heaving), seeing the roots lift when the wind blows, or a tree that has suddenly developed a lean are all signs the roots are failing.
Who is responsible for a boundary tree?
Generally, if the trunk is wholly on your land, it is your responsibility. If it straddles the boundary, it is usually a shared responsibility. Disputes over dangerous trees on boundaries can be complex, so start by getting a clear assessment of the risk to share with your neighbour.
Don’t Wait for the Next Storm
Trees are resilient, but they are not invincible. If you have spotted any of the warning signs mentioned above—cracks, decay, heaving soil, or large dead limbs—it is better to assess the risk now rather than waiting for the next severe weather event.
Early intervention often gives you more options. We might be able to save the tree with corrective pruning or bracing. And if removal is the only safe option, doing it under controlled conditions is far safer and cheaper than removing a fallen tree from your roof.
If you are concerned about a tree on your North Shore property, contact G McColl Tree Services today. We can provide a comprehensive assessment and help you make the safest decision for your home and family.
Photo Source: Image by travel-photography on Freepik