Why danger depends on the defect and what’s underneath it
Arborists assess risk as two things multiplied together. A structural defect in the tree, and a target beneath it worth protecting.
A crack in a trunk over open farmland carries almost no risk, while the same crack over a driveway, a patio, or a path people use daily is a real hazard.
The location underneath the defect is why a tree can be dangerous without being dead or dying.
A weak branch union, a lean that’s developed suddenly, or root damage from nearby digging can all bring down a perfectly green limb with no warning beyond the signs below, since trees don’t have to be dying to fail.
Warning signs of a dangerous tree – By Glasgow’s professional tree surgeons
Any one of the signs below can mean a tree is dangerous, especially where two or three turn up on the same tree together.
A leaning tree that’s new or getting worse
Most trees carry a gentle, permanent lean towards the light, and that’s completely normal.
A lean that’s recent or actively increasing is different, since it usually means the root plate has started to lift on one side.
Cracked or heaved soil at the base, on the side opposite the lean, is the clearest confirmation.
A newly leaning tree with disturbed ground around the roots calls for an urgent professional tree inspection.
Cracks in the trunk and weak branch unions
A crack running along the trunk or a major limb, especially one that’s deep enough to see into, points to a structural failure already in progress.
Two trunks or large limbs growing from the same point, known as codominant stems, often meet at a tight, V-shaped angle that traps bark between them as they grow, a defect called included bark.
The trapped bark never fuses into solid wood, so the join stays weaker than the timber around it for as long as the tree stands.
Splits like these rarely heal, and instead widen in high winds or under the weight of wet snow.
A union that’s failed once is likely to fail again in the same spot.
Fungal growth, cavities and hollow sections
Bracket fungus or mushrooms growing from the trunk or base signal decay inside the wood, often well before any external sign of ill health appears in the canopy.
A cavity that runs less than a third of the way through the trunk diameter is usually still structurally sound.
Once decay has hollowed out much more than that, the remaining wood may not hold under load.
A dull, hollow sound where a healthy trunk would ring solid, tested by tapping the trunk with a mallet, suggests decay worth investigating properly.
Root damage and disturbed ground
Roots hold a tree upright far more than they feed it, and severed or crushed roots don’t show above ground until the tree has already lost significant stability.
Recent excavation, trenching, or heavy machinery working within the canopy’s drip line can sever enough roots to weaken and compromise a tree that still looks completely healthy from the outside.
Fungal growth directly over the root zone, or soil that’s visibly lifted near the base after wind, both point to a root system that’s already struggling to hold the tree upright.
Large dead branches in the wrong place
A few dead twigs scattered through an otherwise healthy canopy are normal and rarely dangerous on their own.
Large dead branches sitting directly over a path, a patio, or somewhere people regularly stand are a different matter, because deadwood loses strength and can fail in wind that a live branch would shrug off.
Storm damage adds its own version of the same risk.
A branch that’s cracked but still hanging in the canopy, sometimes called a hanger, can come down at any time without further warning.
Proximity to buildings and other targets that matter
A house, a car park, a road, overhead power lines, a children’s play area, or simply a path people use every day are all high-value targets, since the same defect carries very different risk depending on what sits beneath it.
A tree may carry that exact same defect and pose almost no risk at all, if nothing stands underneath it, which is why a tree standing alone in the middle of a field is a far lower priority.
A tree that’s structurally sound but overhangs a neighbour’s garden, shed, or car raises the target question in a different way.
It can still become a legal issue if it drops branches or debris, and ongoing nuisance from a badly placed tree is a separate problem from safety risk.
Whoever owns the tree carries the liability if a known hazard causes damage, whether the target sits on their own property or next door.
What to do if you spot these signs: get a professional assessment
Don’t work underneath a tree in your garden, or let anyone linger nearby, once you’ve noticed a real structural defect with a target beneath it.
Photograph what you can see from a safe distance and note whether the tree carries a Tree Preservation Order, since that affects what work can happen and how quickly.
A visual check from the ground only goes so far.
Our certified tree surgeons carry out full tree survey inspections using aerial checks and decay-testing tools where needed.
We assess the defect and the target together before recommending pruning, bracing, or removal based on the actual risk to your property.
Dangerous trees: common questions
Does a leaning tree always mean it’s dangerous?
No. Many trees carry a permanent, gradual lean from growing toward available light, and that’s normal. A lean that’s new or visibly worsening, especially with cracked soil at the base, is the version worth treating as urgent.
Can a healthy-looking tree still be unsafe?
Yes. Structural defects like weak branch unions, root damage, or internal decay can affect a tree that’s still fully leafed and producing normal growth every year.
What counts as a nuisance tree?
A tree that overhangs a boundary, drops debris on a neighbour’s property, or blocks light without any structural defect behind it is usually a nuisance issue rather than a safety one. A pruning schedule sorts an overhanging nuisance tree, while a real structural defect needs the fuller risk assessment described above, which is why the two get diagnosed differently rather than treated as the same complaint.
Who’s liable if a tree on my property causes damage?
Generally, the tree’s owner carries responsibility under the Occupiers’ Liability Act 1957 for damage caused by a hazard they knew about or reasonably should have known about. Regular inspection and acting on clear warning signs is the practical way to manage that liability, since a tree looking fine from a distance proves very little.
Get a proper assessment before deciding with GGM Landscaping
Guessing from the ground is how truly dangerous trees get missed and healthy ones get removed unnecessarily.
Our certified arborists carry out tree surveys across Glasgow and the Central Belt, assessing both the defect and what’s underneath it before recommending any work.
Call 07946 322717 to book a free survey, or get in touch online if you’d rather send photos of what you’ve noticed first.