A tree doesn’t have to be dead to be dangerous. In fact, many hazardous trees are still green and growing — which is exactly why they catch property owners off guard. Hazardous trees are responsible for millions of dollars in property damage every year, not to mention the risk of personal injury. Learning to spot the warning signs early is one of the most important responsibilities a property owner can take on.
Here are the top signs that your tree may be a hazard, and why each one demands immediate professional attention.
1. Dead or Hanging Branches
Deadwood is the most visible and common hazard. Large dead branches — often called “widowmakers” — can break off without warning, even on a calm day. If you see limbs that are bare, bark-free, or hanging precariously in the canopy, they need to be removed before gravity does the work.
2. Cracks, Splits, and Cankers
Vertical cracks that run deep into the trunk are structural time bombs. A crack can indicate that the tree is under stress and literally pulling itself apart. Cankers — sunken, discolored areas on the bark — are often signs of disease or fungal infection that weakens the wood at that location. Both conditions compromise the tree’s ability to support its own weight.
3. Included Bark and Weak Branch Unions
When two branches of similar size grow tightly together, they can form what arborists call an “included bark” union. Instead of strong wood holding them together, there’s bark trapped between them. Over time, this creates a weak point that is prone to splitting, especially under the added load of wind, rain, or ice. Trees with V-shaped unions are far more likely to fail than those with U-shaped attachments.
4. Cavities and Hollows
A tree can be hollow and still look healthy, but its structural integrity is severely diminished. Cavities form when decay eats away the heartwood, leaving only the outer shell. While some hollow trees can live for years, the risk of catastrophic failure increases dramatically, particularly during storms. An arborist can evaluate how much sound wood remains and whether the tree can be retained safely.
5. Root Damage and Soil Disturbance
Roots are the tree’s anchor, and when they’re damaged, the entire tree is at risk. Construction work, digging, paving, and heavy equipment are common causes of root injury. Above ground, you might see thinning foliage, dieback in the crown, or sudden leaning. At ground level, look for cracked or raised soil around the base, fungal growth near the roots, or decayed root flares.
6. Leaning Structure
Not all leans are dangerous. Trees naturally grow toward light or away from prevailing winds. But a lean that develops suddenly, or one that’s accompanied by cracked soil on the opposite side, is a sign of imminent root failure. If the lean is toward a structure, driveway, or area where people gather, treat it as an emergency.
7. Pest Infestations
Borers, bark beetles, and other wood-destroying insects can compromise a tree from the inside out. Look for small holes in the bark, sawdust-like frass, or weeping sap. Advanced infestations can kill a tree and make it structurally unsound within a single season.
What to Do If You Spot These Signs
Hazardous tree assessment is not a DIY task. Many of the most serious defects are invisible to the untrained eye. A certified arborist can perform a thorough risk assessment, using tools like resistographs or sonic tomography to measure internal decay. If the tree is deemed hazardous, removal or extensive mitigation measures should be scheduled without delay.
The peace of mind that comes from knowing your property is safe far outweighs the cost of addressing the problem proactively. When it comes to hazardous trees, hesitation can have serious consequences.