9 Signs a Tree Is Dangerous and Needs to Come Down

Most trees that look frightening are fine, and a fair number that look fine are not. Size and drama are poor guides. What actually matters is whether there is a structural defect, whether the tree is loaded in a way that exploits it, and what would be underneath if it failed.

Here are the nine signs arborists actually look for, roughly in order of how seriously we take them.

1. Lifting or cracking soil at the base

This is the most urgent sign on the list. If the ground on one side of a tree is lifting, cracking, or has developed a slight mound, the root plate is rotating — which means the tree is already in the process of falling, just slowly.

Look on the opposite side to any lean. A tree leaning north will lift soil on its southern side as the plate levers up. It is easy to miss under lawn or groundcover, so get down and look properly.

This is most common after prolonged rain followed by wind. Saturated soil holds a root plate far less securely, which is why most windthrow in Auckland happens in wet-season storms rather than the strongest dry-weather gusts. It is a particular concern on low-lying peaty ground around Takanini and Papakura.

2. A new or increasing lean

A lean by itself proves nothing. Plenty of trees grow with a permanent lean and are entirely stable — particularly on slopes, and on exposed coastal sites in Browns Bay or Takapuna where trees grow away from the prevailing wind.

What matters is whether the lean is new, whether it is increasing, and what the base is doing. A long-standing lean with undisturbed soil and a trunk that has thickened on the compression side is a tree that has adapted. A lean that has appeared or worsened over months, with disturbed soil at the base, is a tree that is failing.

If you are unsure, photograph it against a fixed reference — a fence post, a house corner — and take the same photo in a month.

3. Fungal fruiting bodies

Mushrooms, brackets or conks growing on the trunk, at the base, or on the buttress roots usually mean decay is already well established inside the tree. The visible fungus is only the fruiting body — the reproductive part — and by the time it appears, the fungal network has typically been consuming wood for years.

Where it appears matters:

• At the base or on buttress roots: the most serious location, because that is the structure holding the tree up.
• On the main trunk: indicates decay in the stem, often at an old wound or pruning cut.
• On dead branches only: much less concerning — fungi colonising already-dead wood is normal.
• On a nearby stump: worth noting, as some decay fungi spread through root contact.

Any substantial bracket fungus on a large tree near a building is worth a proper assessment.

4. Cavities and hollows

Here is where intuition misleads people badly: a hollow tree is not automatically a dangerous tree. Trees are engineered as tubes, and a hollow trunk with a thick, sound outer wall can be perfectly stable. Many veteran trees are substantially hollow and stand for decades.

What matters is the ratio of sound wood to the overall diameter, and whether the opening interrupts the tube. As a rough guide, concern rises sharply when the sound outer wall drops below about a third of the stem radius — but that is a rule of thumb, not a test, and it does not account for openings, multiple cavities or the tree's loading.

5. Vertical cracks in the trunk

A vertical crack running down the main stem is a serious structural finding. It means the trunk is already splitting, and it usually indicates either internal decay that has reduced the wood's strength, or mechanical stress the tree cannot handle.

Especially concerning:

• cracks that run into a major branch union;
• cracks with two visible faces that can move independently;
• cracks that have opened further between one season and the next;
• cracks that weep or show discoloured wood.

Distinguish these from bark fissures, which are normal on species like oak, elm and many gums. A structural crack goes through the bark into the wood; a bark fissure does not.

6. Weak or included unions

Where two stems of similar size fork from a common point — a codominant union — the attachment is inherently weaker than a proper branch union. When bark becomes trapped between the two stems as they grow (“included bark”), it is weaker still, because the stems are pressing against each other rather than growing together.

Look for a tight V-shaped fork with a seam of bark running down into it, rather than a rounded U-shape with a visible ridge. Add a heavy, end-weighted limb and a decent easterly and these fail, usually taking a substantial section of trunk with them.

This is a common failure mode in liquidambar, gum and older ornamental species across suburban Auckland.

7. Deadwood in the upper crown

Scattered small deadwood is normal — trees shed lower and interior branches as the crown grows. What is not normal is dieback concentrated at the top and outer edges of the crown, which usually indicates the tree cannot move enough water and nutrients to its extremities. That points to root damage, disease or serious stress.

Large dead limbs are also a straightforward hazard in their own right. Dead wood is brittle, and it is the first thing to come down in wind. If there is a driveway, a deck or a play area underneath, that is worth dealing with before storm season regardless of the tree's overall condition.

8. Recent root disturbance

This one is almost entirely invisible, and it is the reason trees fail years after building work.

Trenching for services, a new driveway, a retaining wall, regrading, or heavy machinery compacting soil over the root zone all damage the structure holding a tree up. The tree may show no symptoms for two or three years, then fail suddenly — either because the anchoring roots decayed, or because the crown outgrew what the remaining roots could hold.

If there has been construction within the canopy spread of a large tree in the last few years, treat that as a reason for assessment even if the tree looks healthy. It is a recurring issue in intensifying suburbs like New Lynn and Onehunga.

9. A sudden change in the surroundings

Trees that grew together shelter each other. Remove a neighbouring tree, take out a shelterbelt, or clear a section next door, and a tree that has stood happily for forty years is suddenly exposed to wind loading it has never experienced and never grew wood to resist.

This is a genuinely underrated risk. If trees around yours have recently come out — on your property or a neighbour's — the remaining ones are more vulnerable for the following few seasons until they adapt.

What to do if you have found one of these

Not every defect means removal

Worth saying, because it costs us work: finding one of these signs does not automatically mean the tree comes out. A hollow with a sound wall may need nothing. Deadwood can simply be removed. An over-extended limb can often be reduced rather than the whole tree taken down. Sometimes the practical answer is moving the target — relocating a garden seat or a trampoline — rather than removing the tree.

Where removal genuinely is the answer, and the tree is protected, document the defect properly before anything happens. An arborist assessment and photographs are what make an urgent works position defensible.

Our on-site assessment is free and we will tell you honestly if your tree can safely stay. See also large and dangerous tree removal and what to do after a storm.

General guidance only, and not a substitute for an on-site inspection of your particular tree. See our disclaimer.

Frequently asked questions