Most serious tree failures are not random events. They are the end point of a process that began years or even decades earlier, with warning signs that were either not noticed or not acted upon. Understanding what those signs look like — and knowing when to call a qualified arborist — is one of the most practical things a homeowner with mature trees can do. This guide covers the key warning signs that a tree may be dangerous, explains what each symptom means structurally, and tells you what to do if you spot them.
Whether you’re in Nottingham, Derbyshire, or anywhere across the East Midlands, the same principles apply. Trees do not distinguish between postcodes — but acting before a problem becomes an emergency will always save time, money, and in some cases far worse.
Why Tree Failure Is Rarely Sudden
It is a common perception that trees fall without warning. In reality, the vast majority of tree failures — root plate uprooting, major branch failures, and stem fractures — are preceded by visible indicators that a qualified arborist would identify during an inspection. The problem is that many of these indicators require you to know what to look for, and some are only clearly visible at certain times of year or from certain angles.
Professional arborists use a process called a Visual Tree Assessment (VTA) to systematically evaluate the whole tree — roots and soil zone, the base, the stem, the major branches, and the crown — and identify any signs of structural compromise, disease, or decay. Where a VTA identifies a potential concern, more detailed investigation (including drilling, resistograph testing, or soil probe investigations) may be recommended. The VTA is the starting point for any formal tree risk assessment.
Warning Sign 1: Cracks or Splits in the Main Stem or Major Branches
Visible cracks running along or across the main stem, or at the union of major branches, are one of the most serious structural warning signs a tree can display. They typically indicate that the wood fibres have failed under mechanical stress — whether from wind loading, frost action, disease-weakened wood, or structural imbalance in the crown.
Different types of crack carry different levels of risk:
- Longitudinal cracks (running along the grain) — can indicate shear failure or advanced fungal decay in the central core
- Transverse cracks (running across the stem) — serious; indicate compression failure, often associated with root damage or soil movement
- Cracks at branch unions — particularly concerning at co-dominant stem unions, where a crack may indicate that a split is beginning to propagate
If you notice a crack that appears to be widening — compare photographs taken a month apart — treat this as an urgent matter requiring professional assessment without delay. A crack does not automatically mean the tree must come down, but it does mean the tree needs a qualified arborist’s opinion before the next storm season.
Warning Sign 2: Fungal Fruiting Bodies at the Base or on the Stem
Fungal brackets, shelves, or mushrooms growing from the base, root flare, or lower stem of a tree are almost always a sign of significant internal decay. The fruiting body you can see represents only a small fraction of the fungal mycelium network working through the wood; by the time brackets are externally visible, the decay process may have been active for years and the structural consequences can be severe.
Species identification matters here. The most commonly encountered bracket fungi on amenity trees in the East Midlands include:
- Ganoderma species (artist’s bracket, lacquered bracket) — associated with white rot of the roots and butt; one of the most common indicators of serious structural compromise
- Meripilus giganteus (giant polypore) — appears at the base as large, overlapping, fan-shaped brackets in late summer and autumn; associated with root and butt decay in beech, oak, and other broadleaved species
- Phaeolus schweinitzii (dyer’s mazegill) — causes brown rot in the roots and butt of conifers and some broadleaves; a significant structural concern
- Kretzschmaria deusta (brittle cinder) — one of the most structurally dangerous; causes a type of decay that can progress rapidly without obvious external symptoms, leaving very little safe wood remaining
If you see any fungal fruiting bodies at the base or on the stem of a garden tree, arrange a professional inspection. Do not assume the tree is safe because it still has a full crown of leaves.
Warning Sign 3: Significant Deadwood in the Crown
Deadwood is a natural and ecologically important part of any mature tree’s life cycle, and in the right context — high in the crown of a tree away from targets below — it should be left in place. However, deadwood above 50mm diameter positioned over paths, driveways, buildings, garden furniture, or any area where people regularly spend time presents a genuine risk.
Dead branches retain their weight for a period after dying, but as they dry and lose moisture the wood becomes increasingly brittle. The breaking strength of dry dead wood is significantly lower than living wood, and in wind conditions the dead sections are the first to fail. A dead branch of 100mm diameter falling from 12 metres carries enough kinetic energy to cause serious injury or write off a vehicle — and unlike a live branch, there is no bending or deflection before failure.
The key questions for a deadwood risk assessment are: What is the diameter of the dead material? How high is it above the target below? How many people are regularly under it? Is it still attached at the branch collar, or has the union already failed? We address all of these during a standard tree inspection.
Warning Sign 4: A Lean That Has Developed or Changed
Many healthy trees grow at a permanent slight lean and are entirely stable — they have developed an asymmetric root system that counterbalances their angle. The warning sign is not a lean per se, but a lean that has changed: a tree that was upright or leaning slightly in one direction and is now noticeably more inclined. This change indicates that the root anchorage is failing progressively — and in wet soil conditions this process can accelerate rapidly.
Associated signs of root plate failure include:
- Raised or cracked soil around the upwind root plate
- Root cracking or snapping sounds in previous wind events
- Exposure of roots at the soil surface on the windward side
- Soil heaving or compression around the base
A tree showing these signs in combination with a recent lean change should be treated as an urgent situation. In saturated soils the root plate can fail completely in a single wind event. Keep people away from the fall zone and seek professional advice immediately.
Warning Sign 5: Co-dominant Stems with Included Bark
A co-dominant stem union is where two stems of similar diameter grow from the same point, competing for the same vertical space. As they grow together, bark becomes trapped between them in a V-shaped wedge — this is called included bark. Unlike a normal branch union, where wood fibres from both stems interweave and create a mechanically strong joint, a union with included bark has no such fibre integration. The two stems are essentially sitting against each other rather than growing together, and the junction can fail catastrophically under wind or snow loading.
Included bark is common in species that are prone to co-dominant development, including Prunus (flowering cherry), Betula (birch), and some Acer species. It is one of the most important structural defects to identify early, because intervention — removing one stem while the tree is still relatively young — is straightforward. Addressing it in a mature tree is significantly more complex and expensive, and in the worst cases the tree becomes un-retainable.
Warning Sign 6: Epicormic Growth and Progressive Crown Dieback
Epicormic growth — clusters of small, fast-growing shoots appearing on the main stem or from the base of the trunk — is the tree’s emergency response to stress. The tree is bypassing its normal shoot development pathway and activating dormant buds to try to restore photosynthetic capacity quickly. Triggers include: waterlogging, soil compaction, root damage from nearby construction, significant crown dieback, disease, and previous over-pruning.
On its own, epicormic growth is a symptom rather than a danger. But it tells you that the tree is under stress and that the cause of that stress should be identified. Progressive crown dieback — where increasing proportions of the crown fail to come into leaf over successive seasons — combined with epicormic growth at the base typically indicates a tree in significant decline, with structural implications that need professional assessment.
Warning Sign 7: Evidence of Previous Poor Pruning
Topping (removing the entire main crown and leaving only large stub ends), lion-tailing (stripping all interior and lower branches to leave foliage only at the tips), and flush cuts (removing branches without leaving the protective branch collar) are all forms of harmful pruning practice that create long-term structural problems. They are unfortunately common in the older residential tree stock across Nottinghamshire and Derbyshire.
A topped tree generates vigorous regrowth at the cut points, but these new shoots attach by scar tissue rather than properly integrated wood. As they grow and become heavier over years, the attachment remains weak — and the branches become progressively more likely to fail. If you have moved into a property and found a tree that has been significantly topped in the past, a professional condition assessment is a sensible early step.
What Happens During a Professional Tree Inspection
A professional tree inspection by a qualified arborist follows a systematic process:
- Root zone and soil check — looking for surface roots, soil heave, fungal fruiting bodies, and signs of soil compaction or disturbance
- Stem and buttress assessment — checking for cracks, cavities, fungal growth, wound responses, and any lean change indicators
- Branch and crown evaluation — identifying deadwood, co-dominant unions, included bark, previous poor pruning wounds, and crown dieback
- Target assessment — identifying what is in the fall zone beneath any identified defects
- Risk assessment and recommendations — a proportionate risk evaluation that balances the probability of failure, the severity of the consequence if it occurs, and the value of the tree
Where the inspection identifies concerns, the arborist will recommend appropriate management options — from routine deadwood removal through to structural pruning, crown reduction, cabling, or in appropriate cases removal. All recommendations are proportionate to the actual risk, not a default instruction to remove everything in doubt.
Internal Links to Relevant Information
For guidance on specific tree issues, see also: our ash dieback guide for Nottinghamshire homeowners, our guidance on what to do with a storm-damaged tree, and our full guide to Tree Preservation Orders.
Frequently Asked Questions
How much does a tree inspection cost?
A site visit and verbal assessment is included free with any quote from TB Tree Care. A formal written tree condition report — suitable for insurance, legal, or planning purposes — is a separate service that we can quote for based on the scope required.
My tree has a cavity — does that mean it must come down?
Not automatically. Cavities are a normal feature of mature trees and do not in themselves indicate structural failure. The key factors are the position and extent of the cavity, how much sound wood remains, and what the targets are beneath the tree. A professional assessment gives you a clear, evidence-based answer.
How often should a mature garden tree be inspected?
For most mature trees in residential gardens, an inspection every three to five years is a reasonable baseline. Trees near high-use targets (footpaths, driveways, buildings) or trees showing any of the warning signs in this guide should be inspected more frequently.
Can I inspect my own tree?
You can carry out a basic visual check from ground level, and knowing what to look for (as described in this guide) means you will notice changes sooner. However, a full Visual Tree Assessment requires specific arboricultural training, knowledge of decay fungi, and in some cases the ability to get close to the stem and upper crown. For any tree near a target, professional assessment is always the more reliable approach.
Concerned about a tree in your East Midlands garden?
We carry out tree inspections and risk assessments across Nottinghamshire and Derbyshire. NPTC qualified, fully insured, and familiar with local TPO requirements.
