Seven signs a tree is dangerous, and what to do about each
The seven signs worth acting on: fungal brackets at the base, fresh cracks or splits in the trunk, a new or worsening lean, dead branches in the crown, lifting soil around the roots, cavities and hollows in the main stem, and the thinning crown of ash dieback. Any one of them over a roof, road or footpath justifies a professional inspection, and a sudden lean after a storm justifies an urgent one.
Last updated: August 2026.
Trees rarely fail without warning. Almost every storm-damage callout across Teesside, the sycamore on the garage in Linthorpe, the poplar across the footpath at Seaton Carew, showed at least one of these signs months earlier. Here is what to look for, in rough order of how often we hear "I wish I'd got that looked at".
1. Fungal brackets at the base or on the trunk
Hard, woody brackets (conks) growing from the trunk or buttress roots mean decay fungi are inside the tree digesting its structure. Honey fungus produces honey-coloured toadstools in autumn clumps and black bootlace strands under the bark; Ganoderma brackets on beech and sycamore signal serious butt rot. A tree can look perfectly green and healthy while its base is hollow. Brackets at the base of a mature tree near a house are always an inspection, not a watch-and-wait.
2. Fresh cracks and splits
Vertical cracks in the trunk, or a split where two main stems join (a V-union with bark rolling inwards), mean the tree is already moving under load. Cracks that weep, or that you can see daylight through, are urgent. Co-dominant stems on mature ash and sycamore are the classic Teesside failure: two trunks sharing one weak junction, waiting for an easterly.
3. A new lean, or an old lean that has moved
Plenty of trees lean their whole lives without incident. What matters is change. A lean that appeared after a storm, or one that has visibly worsened over a season, means the root plate is failing. Compare photographs if you have them. Any sudden lean is a same-week inspection, and if the tree is over a building or road it is an emergency call.
4. Dead wood in the crown
Dead, barkless branches high in the crown, "stag-headed" tips, are the tree telling you something is wrong below. Individual dead branches fall without warning in still air (so-called summer branch drop), which is why dead wood over a patio or a child's play area should not wait for winter. Crown dieback that spreads year on year points to root problems or disease.
5. Lifting soil and root plate movement
Look at the ground, not just the tree. Soil heaving or cracking on one side of the trunk, or a gap opening on the other, means the roots are losing their grip. On Teesside's heavy boulder clay this is the classic winter failure mode: saturated ground, a westerly gale, and a root plate that simply rocks out. Trees on the low, wet ground near the Tees at Thornaby and the coast at Seaton Carew are the ones to watch after prolonged rain.
6. Cavities, hollows and old pruning wounds
A cavity does not automatically condemn a tree, sound trees carry hollows for decades, but size and position matter. A hollow at the base, or a cavity combined with fungal brackets, or an old topping wound now rotting into the main stem, all change the maths. Big horizontal cavities in the trunk within falling distance of a house justify a decay assessment, sometimes with a resistograph reading rather than guesswork.
7. Ash dieback
Ash dieback (Hymenoscyphus fraxineus) is now established across the North East, and Teesside's older ash, in Acklam and Linthorpe back gardens, along the railway cuttings and on the escarpment edges, is showing it. The signs: diamond-shaped lesions on the bark, dead black leaf shoots in summer, and a crown thinning from the top down. The danger is not just that the tree dies. Dead ash turns brittle fast, and brittle ash cannot be climbed or rigged conventionally, which makes removal slower and dearer the longer it stands. An ash at 30% dieback is a cheaper and safer removal than the same tree at 70%.
What to do when you spot one
Do not climb, and do not let an unqualified "man with a saw" make it safe. Photograph the sign, note what the tree would hit, and get a professional inspection. If the tree is protected (a TPO or conservation area), dangerous trees are exempt from consent, but the evidence needs recording first, photographs before cutting, and five days' notice to the council where practicable. If a tree is down or hung-up after a storm, treat it as loaded spring: storm-damaged timber under tension causes more injuries than chainsaws.
None of this replaces an in-person look. If any of the seven signs is present over a roof, road or footpath, describe it in the quote form with a photo and mark it urgent.