Signs Your Tree Is Dangerous or Dying — and When to Call an Arborist

The Short Answer

The clearest warning signs that a tree is dangerous are fungal brackets at the base, cracked or lifting soil around the roots, a vertical split or crack in the main stem, hollow or soft wood at the base, and large deadwood held in the crown. Any of those combined with a recent change — a new lean, soil movement, or a sudden increase in deadwood — warrants a professional inspection immediately rather than at your convenience.

Start at the roots, not the branches

Most catastrophic tree failures in the South East are root or base failures, not branch failures, and they give warnings that are easy to see once you know what to look for. Walk a full circle around the trunk at a couple of metres’ distance and look at the ground first.

Cracked, domed or lifted soil on one side of the tree, with a corresponding depression on the other, means the root plate is moving. This is the single most serious sign on this page. So is a gap opening between the stem and the soil, and turf that has torn or rucked in an arc around the base. Trees showing root plate movement can fail without further warning in the next strong wind.

Look also for severed roots. Trenching for drainage, a new driveway, a patio or an extension within the rooting area cuts the anchorage on that side of the tree, and the failure often follows one to three years later, not immediately. Where major roots have been cut on one side and the tree leans the other way, treat it as urgent.

Fungal fruiting bodies at the base or on surface roots are the third root-level signal. Brackets of Meripilus giganteus around a beech, honey fungus rhizomorphs under the bark, or Ganoderma brackets on the buttress all indicate decay in the structural wood, and the visible fruiting body is the late stage of a process that has been running for years.

Then the stem

Run your eyes up the trunk. A vertical crack or seam — particularly one that is longer than a metre, or that opens and closes as the tree moves in wind — indicates that the stem is already partly failed. Bark that has come away in sheets, sunken or discoloured patches, and weeping or bleeding points all suggest dysfunction underneath.

Cavities and hollows are more nuanced than most people assume. A hollow trunk is not automatically dangerous; trees are engineered as tubes and a surprising amount of the centre can be missing without compromising strength. What matters is the ratio of sound residual wall to radius, whether the opening interrupts the tube, and whether decay is advancing. That judgement needs an arborist, sometimes with a decay-detection device, rather than a guess.

Check the forks. Where two stems of similar size rise from a single point and the bark is pinched inwards between them rather than forming a raised ridge, that is included bark — a weak union with no interlocking wood, and one of the commonest causes of large limb failure in mature sycamore, ash, lime and horse chestnut. Included unions on big co-dominant stems above a house or driveway should be assessed and often need bracing or reduction.

Finally the crown

Deadwood is normal in every mature tree, and small dead twigs are not a concern. What matters is large deadwood — anything above around 50mm diameter — particularly where it sits over a footpath, driveway, garden seating or a neighbour’s property. Dead limbs shed without warning and in still weather as often as in wind.

A crown that is noticeably thinner than the same species nearby, leafing out late, holding smaller leaves than usual, or showing dieback starting at the branch tips and working inwards, is telling you the tree is struggling. Two or three consecutive seasons of that pattern usually indicate root damage, disease or a fundamental site problem.

Hanging or snapped limbs caught in the canopy — “widow-makers” — are an immediate hazard and should be treated as an emergency. So should a large limb that has partially torn from the stem but is still attached, because the remaining fibre gives no reliable warning of when it will part.

• Fungal brackets on the base, buttress roots or main stem
• Cracked, heaved or lifting soil around the root plate
• A new or increasing lean, especially after wind or heavy rain
• Vertical cracks or seams in the trunk, or bark falling away in sheets
• Included bark at a fork between co-dominant stems
• Large deadwood, hanging limbs or partially torn branches in the crown
• Thin, late or undersized foliage compared with neighbouring trees of the same species
• Recent excavation, trenching or paving within the rooting area

Lean: when it matters and when it does not

A tree that has always leaned is usually fine. Trees respond to wind loading and light availability by laying down reaction wood, and a long-standing lean is generally supported by an adapted root plate and a thickened stem on the appropriate side.

A new lean is an entirely different matter. If the angle has changed noticeably in the last year, or after a storm, the root plate or stem has moved and the tree should be inspected immediately. The give-away is the ground: a long-standing lean has undisturbed turf and level soil at the base, while a recent one has cracking, doming or a visible gap.

The other useful clue is the crown shape. A tree that grew leaning will have a crown that has corrected itself upright over time, producing a curved stem. A tree that has recently moved keeps its original crown geometry and simply tips — branches on the low side end up closer to the ground than they were.

What counts as an emergency

Call for emergency attendance the same day if a tree or major limb has fallen and is blocking a road, driveway or footpath; if there is a hanging or partially detached limb over any area people use; if the root plate is visibly lifting; if a stem crack has opened; or if a tree is resting on a building, wall, fence or vehicle.

If the tree is touching or has brought down power lines, do not approach it and do not attempt to move anything. Call the electricity distribution network operator’s emergency number and keep everyone at least 10 metres clear. Blocked public highways are the local authority’s responsibility in the first instance.

Everything else — increasing deadwood, a fungal bracket found on a routine walk round, thinning canopy, an included fork above the garage — needs a professional inspection soon, but not tonight. Book a survey, keep people away from the immediate area if you are unsure, and get a written assessment rather than a verbal opinion.

Your legal duty of care

As the owner or occupier of land you have a duty of care under the Occupiers’ Liability Acts and in common law negligence toward people and property that could be harmed by a tree on your land. The standard is not perfection; it is that you took reasonable steps in proportion to the risk.

In practice that means trees in high-use areas — over a public pavement, a driveway, a school route, a busy garden — warrant more frequent and more formal inspection than a tree in the middle of a field. For most domestic properties, a walk-round by the owner each year and after significant storms, plus a professional inspection every three to five years on large mature trees near targets, is a defensible regime.

Documentation is what turns a sensible regime into a defence. Dated photographs, a written survey report and records of the work carried out demonstrate that you acted reasonably. If a claim is ever made against you, that paperwork is the difference between a defensible position and an indefensible one.

What an inspection involves

A visual tree assessment starts on the ground: species, dimensions, position and targets, then a systematic examination of root plate, buttress, stem, unions and crown, usually with binoculars for the upper canopy. Where a defect needs closer investigation, the next stage is an aerial inspection by a climber or a decay-detection test such as sounding, resistance drilling or tomography.

The output should be a written report that names the defects, rates the risk, recommends specific work with a timescale, and sets a date for re-inspection. That report also serves as your evidence of reasonable care, and as supporting material if a council application or an insurance claim follows.

Not every defective tree needs removing. Crown reduction to cut wind sail, dynamic bracing across a weak union, deadwood removal, or simply moving the target — relocating a parking space or a garden bench — frequently resolves the risk while keeping a tree that has taken eighty years to grow.

How to check a tree for danger signs

A ground-level inspection routine any property owner can carry out in ten minutes, working from the roots up.

1. 1

   Walk a full circle around the tree

   Stand back a few metres and view the tree from every side. Look for a lean, an uneven crown, or branches that sit lower than they used to.

2. 2

   Examine the ground and root plate

   Look for cracked, domed or lifted soil, torn turf in an arc around the base, gaps between stem and soil, and any recent trenching or paving within the rooting area.

3. 3

   Inspect the base and buttress for fungi and decay

   Check for bracket fungi, soft or hollow-sounding wood, weeping points and bark falling away. Note anything found with a dated photograph.

4. 4

   Check the stem and forks

   Look for vertical cracks or seams, sunken patches, and forks where the bark is pinched inwards rather than raised, which indicates a weak union.

5. 5

   Scan the crown with binoculars

   Identify large deadwood, hanging or partially torn limbs, and compare canopy density and leaf size against nearby trees of the same species.

6. 6

   Act on what you find

   Treat hanging limbs, root plate movement, new leans and open stem cracks as same-day emergencies. Book a professional survey for anything else, and keep dated photographs as your record.

Related Pages

Questions Answered

Frequently Asked Questions