Signs a tree is unsafe: cracks, cavities and leaning explained

Trees can become unsafe when their structure is weakened, even if their leaves look healthy. Cracks, cavities, sudden leaning and movement around the roots may indicate a risk of falling branches or the whole tree failing, so recognising these signs early can help you protect people and property.

Reading structural warning signs

Some changes are easy to notice, while others need a trained eye. A single defect does not always mean a tree must be removed, but its size, position, condition and proximity to buildings, roads or play areas all affect the level of risk.

Sudden leaning or movement at the roots

A tree that has always leaned slightly may be stable, but a new or rapidly worsening lean is more concerning. It can suggest root damage, soil failure or a weakened trunk, particularly after strong winds or prolonged heavy rain.

Look at the ground around the base for raised soil, lifted roots, cracks in the earth or a root plate that appears to be moving. Keep people and pets away from the area, avoid standing beneath the canopy and arrange a professional inspection promptly.

Fresh cracks in the trunk or major branches

Long, deep or widening cracks can reduce the strength of a trunk or limb. Pay particular attention to cracks that run along a union between stems, extend through a large branch or have exposed, fresh-looking wood and moisture inside.

Do not touch, climb or attempt to brace the tree yourself. Restrict access beneath it and, if the crack has appeared suddenly or the tree is next to a building, road or regularly used path, seek urgent advice from a qualified tree professional.

• Keep children, pets and visitors away from the tree.

• Use alternative routes around the canopy and avoid parking beneath it.

• Photograph the defect from a safe distance to help with an initial discussion.

• Report any immediate obstruction or danger to the relevant landowner or authority.

Other signs that deserve attention

Cavities, hollowing and weak unions

A cavity may form after an old wound, broken branch or decay process. Hollowing can reduce the amount of sound wood supporting the tree, although a hollow tree is not automatically dangerous. The remaining wood, cavity location and loads carried by the crown all need to be assessed together.

Multiple co-dominant stems are another structural concern, especially when they join with a narrow, V-shaped union. Tight unions can contain included bark, where bark becomes trapped between stems and prevents a strong connection from forming. Keep clear if the union is splitting, cracked or supporting heavy limbs.

Dead tops, hanging limbs and broken branches

A dead top, known as a dead crown or dead leader, may be caused by root problems, storm damage or other stress. Dead wood can become brittle and fall without much warning, while hanging or partially broken limbs are an immediate overhead hazard.

Do not pull down a hanging branch or stand underneath it to inspect the damage. Keep the area below the tree closed off and contact a tree surgeon, particularly if the limb is over a home, road, entrance or public space.

Fungal fruiting bodies at the base

Mushrooms or bracket fungi around the base can indicate decay in the roots, buttress or lower trunk. Some fungi live on dead material without seriously affecting a living tree, but fruiting bodies close to the root flare should always be treated as a reason for professional assessment.

Do not remove the fungus and assume the risk has gone. Note its location and appearance from a safe distance, keep people away if the tree is showing other movement or cracking, and arrange an inspection.

What a professional tree assessment involves

A qualified arborist will usually begin with a visual tree assessment, examining the trunk, branches, unions, root flare, surrounding soil and the tree’s setting. They will consider defects alongside species, age, recent weather, targets such as buildings and paths, and signs of movement or decay.

A detailed tree survey may be appropriate where the tree is close to valuable property, forms part of a development site, has several significant defects or needs a written management plan. Further investigation, such as probing or specialist testing, may be recommended where visual checks cannot establish how much sound wood remains.

What not to do

Do not top the tree, climb it with a ladder or cut large limbs without the correct training and equipment. These actions can create larger wounds, destabilise branches and put you directly in the fall zone. They may also breach nesting bird protections, tree preservation controls or other local requirements.

Instead, restrict access and wait for professional advice. If a tree is touching power lines, stay well away and contact the electricity network operator rather than approaching it.