A hazard tree is any tree with a structural defect that creates a credible risk of failure onto a target — a building, a vehicle, a walkway, a person. Hazard assessment is what we are trained to do, and it is built around a small number of repeatable visual cues. You can learn the basics in an afternoon.
What follows are the seven indicators we use on every property walk. None of them is, on its own, a death sentence for a tree. Several of them together are.
1. Mushrooms or conks at the base
Fungal fruiting bodies — shelf fungi (conks), mushrooms, or brackets — appearing at the base of a trunk or on exposed roots are almost always a sign of advanced internal decay. The fruit body is the visible 5% of the organism; the other 95% is mycelium already inside the wood. Ganoderma, Armillaria, and Inonotus are the species we see most often on Florida hardwoods, and each indicates a specific type and severity of decay.
Action: get a resistograph reading. A trained arborist can quantify residual wood strength and give you a real probability of failure.
2. Cracks running vertically up the trunk
Vertical cracks indicate internal shear stress, usually from a structural defect — a hidden cavity, a co-dominant union splitting, or wind loading exceeding what the wood can handle. Long, deep, or widening cracks are urgent. Surface frost cracks on younger trees are not.
3. New lean
Compare the tree to old photos. A tree that suddenly leans more than it used to, especially with soil heaving on the side opposite the lean, is in active root failure. This is the most dangerous indicator on the list and the easiest to miss because the change happens slowly until the day it does not.
4. Co-dominant stems with included bark
Two trunks of similar diameter meeting in a tight V-shape, with bark pinched between them, are a textbook failure point. The bark prevents the wood from fusing properly, and the union fails — often catastrophically and often without warning — under wind or ice load.
5. Deadwood greater than two inches in diameter
Small deadwood is normal and expected. Large deadwood is a falling-limb hazard regardless of the rest of the tree's health, and large deadwood concentrated on one side of the canopy suggests a root or vascular problem on that side.
6. Cavities and hollows
A cavity is not automatically a death sentence — trees can lose substantial interior wood and remain structurally sound, as long as the residual outer wood shell is at least one-third of the trunk diameter. Below that ratio, failure risk climbs sharply.
7. Recent construction or grade change within the dripline
If anyone has trenched, paved, regraded, or driven heavy equipment within the dripline in the last five years, the tree is in some stage of decline whether it shows yet or not. Root damage takes three to seven years to express itself in canopy symptoms, and by then it is usually irreversible.