What Makes a Tree a Hazard
A hazard tree is one that presents a meaningful risk of failure (whole tree, major limb, or significant section falling) over a target — a structure, vehicle, or area where people are present.
The key factors in hazard assessment are:
- Likelihood of failure — how structurally sound is the tree?
- Target — what would the tree or limb fall on?
- Consequences — what's the severity of impact if failure occurs?
A tree that's in poor structural condition but in a remote area with no targets is lower priority than a marginally defective tree directly over a bedroom. Risk is a combination of probability and consequence.
This guide covers the signs you can observe from the ground. It's not a substitute for professional assessment of trees you're concerned about, but it helps you know what to look for and which trees warrant a closer look.
Signs of Potential Failure: Ground Level
Root zone problems:
Heaving soil on one side of the base while the tree leans away suggests root plate failure on the tension side. This is a significant warning sign indicating potential whole-tree failure risk.
Fungal conks (shelf fungi, bracket fungi) growing on the root flare or base of the trunk indicate internal decay. The fungal body you see is the reproductive structure of an organism that's been decomposing wood inside the tree for years. By the time conks are visible externally, internal decay is often extensive. Not all conks indicate imminent failure — species, location, and size matter — but any fungal growth at the base warrants assessment.
Soil separation around the base, or visible root damage from construction, trenching, or soil grade changes.
Root flare not visible — if the trunk appears to go straight into the ground without a visible flare, the tree may have been planted too deep or had soil accumulated against it. This can lead to girdling roots and structural issues.
Trunk problems:
Large cavities in the trunk — particularly cavities that open into a hollow interior — indicate decay of the central wood. The significance depends on the amount of sound wood remaining around the cavity. Cavities that extend deeply into the trunk's structural core are more concerning than surface cavities.
Cracks — vertical cracks running along the trunk, or horizontal cracks, can indicate both current stress and historical failure events. Cracks in the crotch area between a major leader and the trunk are particularly concerning.
Co-dominant stems with included bark — where two roughly equal stems arise from the same point and the bark between them appears embedded (included) rather than ridged outward, the attachment between them is structurally weak. This is one of the most common structural defects leading to major limb or stem failures.
Cankers — sunken, discolored, or abnormal areas of bark that may indicate disease-related wood decay. Some cankers are cosmetic; others indicate active fungal decay of structural wood.
Lightning damage — vertical bark splits, often spiraling, with scorched or missing bark sections. The structural impact of lightning varies; some trees recover fully, others develop internal decay pathways at the damage site.
Signs of Potential Failure: Upper Crown
Dead limbs:
Dead limbs lose their flexibility over time and break more easily than living wood. The significance depends on size, location, and what's below. Deadwood directly over a structure or high-traffic area is a priority regardless of tree overall health.
Identify dead limbs by: absence of leaves when surrounding branches are leafed out; gray, cracking bark vs green or brown living bark; peeling bark; presence of woodpecker activity (often targeting deadwood with insects).
Hanging limbs:
A hanging limb — sometimes called a "widow maker" — is a broken branch still caught in the crown rather than having fallen. These can remain suspended for months before coming down, and they drop with no warning. Any hanging limb over a target is an immediate priority.
Poor structure:
Trees that have been topped develop weakly attached water sprouts at each cut point. These grow quickly but are attached only to the callus tissue at the wound site, not with the structural attachment of normally developed branches. Water sprouts from old topping cuts commonly fail, especially as they grow heavy and the weak attachment can't support the weight.
Crown dieback:
Dying back of the outer crown — branches that were alive and are no longer leafing out — can indicate root problems, vascular disease, drought stress, or other systemic issues. Progressive crown dieback (worsening from year to year) is a significant indicator that the tree is in decline.
When to Call a Professional
Get a professional assessment when:
- You see fungal conks at the base or on the trunk
- The tree has significant cavities or visible internal decay
- Major limbs are dead or hanging over structures or occupied areas
- The tree has a lean that appears to be progressing, or there's soil heaving at the base
- The tree is in significant decline and positioned where failure would cause damage
- You're dealing with a large, high-value, or complex situation — pre-storm season assessment, insurance claim, post-storm evaluation
ISA-certified arborists use standardized methods for hazard rating and can provide written assessments for insurance documentation, permit applications, or your own records.
Tree hazard assessment in Tallahassee? Call (850) 570-4074 or request an inspection online.