Last updated: March 28, 2026 | By Carlos Mendez, ISA Certified Arborist
A falling tree can cause catastrophic damage to homes, vehicles, and power lines, and poses a serious risk to human life. Learning to identify the warning signs of a structurally compromised tree allows you to take action before disaster strikes. Here are the five most important indicators that a tree on your property may be at risk of failure, and what you should do about each one.
1. Visible Root Damage and Soil Heaving
A tree’s root system is its anchor, and when roots are compromised, the entire tree becomes unstable. Root damage is often caused by construction activity, grade changes, soil compaction, or root rot from persistent moisture. Because most structural roots extend in the top 12 to 18 inches of soil, even seemingly minor ground disturbances can affect stability.
Warning signs of root problems include:
- Soil heaving: Cracked or raised soil on one side of the tree, especially opposite a lean, indicates roots are pulling out of the ground
- Exposed roots: Erosion or grade changes that expose major roots to damage from mowers, foot traffic, or weather
- Mushrooms at the base: Fungal fruiting bodies growing near the trunk or on surface roots indicate internal decay in the root system
- Severed roots: Construction trenching, sidewalk installation, or utility work within the drip line that cut major roots
- Circling roots: Roots that wrap around the trunk base (girdling roots) strangle the tree’s vascular system and weaken the root-trunk connection
A tree with compromised roots may appear healthy in its canopy for years while its anchor system deteriorates invisibly below ground. Professional arborists use tools like air spades and resistograph drills to assess root and trunk integrity without damaging the tree.
2. Leaning Trees That Have Changed Angle
Many healthy trees grow with a natural lean, and this alone is not a problem. The critical distinction is between a tree that has always leaned and one that has recently started leaning or increased its angle of lean. A sudden or progressive lean indicates active root failure or soil instability that will eventually result in the tree falling.
To determine if a lean is progressing, look for cracked soil at the base opposite the lean direction, exposed roots on the lean side lifting out of the ground, and changes in the gap between the tree and nearby structures over time. Photograph the tree from the same vantage point monthly and compare images to detect gradual changes that are difficult to notice day to day.
A tree leaning more than 15 degrees from vertical is at elevated risk of failure. Trees that have suddenly developed a lean after a storm have likely experienced root plate failure and should be treated as emergencies. Do not attempt to cable or brace a tree that is actively leaning; evacuation of the fall zone and professional removal are the safe responses.
3. Trunk Cracks, Cavities, and Decay
The trunk is the tree’s main structural column, and defects in the trunk directly affect the tree’s ability to support its own weight and withstand wind forces. Deep cracks, cavities, and internal decay reduce the load-bearing capacity of the trunk, sometimes to the point of sudden failure.
Inspect tree trunks for vertical cracks that extend through the bark into the wood, open cavities where branches have broken off or decay has created holes, soft or spongy areas on the trunk surface that indicate internal rot, cankers or areas where the bark is missing and the wood beneath is discolored, and seeping sap or sawdust at the base indicating borer insect activity. A general rule in arboriculture states that if a cavity or decay column encompasses more than one-third of the trunk’s cross-sectional area, the tree’s structural integrity is significantly compromised.
Modern arborists use sonic tomography and resistance drilling to map internal decay without cutting into the tree. These assessments cost $200 to $500 but provide accurate data for decision-making about trees that appear healthy externally but may be hollow or decayed internally.
4. Dead Branches and Crown Dieback
Dead branches in the upper canopy, called widow-makers in the tree industry, are falling hazards that can drop without warning. Large dead branches weigh hundreds of pounds and fall with enough force to cause serious injury or death. Beyond the immediate falling hazard, widespread dead branching indicates the tree is in decline and may be approaching structural failure.
- Individual dead branches: Can be pruned by an arborist to eliminate the falling hazard. Cost ranges from $200 to $800 depending on tree height and branch size.
- Crown dieback (20-50%): Significant die-back suggests root problems, disease, or environmental stress. The tree should be evaluated by a certified arborist.
- Crown dieback (50%+): More than half of the canopy showing dead branches usually indicates the tree is dying and should be removed before structural failure.
Look for dead branches by comparing sections of the canopy in early summer when healthy branches are fully leafed out. Dead branches remain bare and become obvious against the surrounding green foliage. Any dead branch larger than 4 inches in diameter over a target area like a walkway, driveway, or seating area should be removed promptly.
5. Multiple Trunks with Included Bark
Trees with two or more trunks originating from the same point often develop a structural weakness called included bark. Instead of the trunks forming a strong, reinforced union, bark becomes trapped between them, preventing the wood from fusing properly. This creates a weak point that is prone to splitting, especially during wind storms or when weighted by ice or heavy foliage.
Included bark is identified by a visible seam or crease where the trunks meet, rather than a rounded, solid-looking union. As the trunks grow in diameter, they press against each other and the trapped bark decays, further weakening the connection. Many catastrophic tree failures during storms occur at included bark unions that appeared perfectly stable in calm conditions.
For valuable trees with included bark, professional cabling and bracing systems can reduce the risk of splitting. Steel cables installed high in the canopy limit how far the trunks can move independently, and threaded rods through the union point reinforce the connection. These systems cost $300 to $1,000 and require inspection and maintenance every 3 to 5 years.
If you have identified any of these warning signs on trees on your property, schedule a professional tree risk assessment with a certified arborist immediately. Do not wait for a storm to turn a hazard tree into a disaster. A $200 to $500 assessment can prevent thousands of dollars in property damage and protect your family’s safety. Contact a qualified tree service today for a professional evaluation.