A tree doesn’t need to be visibly dead to be dangerous. Some of the most damage-prone trees in Rochester yards are still fully leafed out, and the defects that matter most — a cracked trunk, a shifting root plate, a cavity hidden behind healthy-looking bark — are easy to miss unless you know exactly where to look. This checklist walks through what a certified arborist actually checks during a hazard assessment, so you can tell the difference between a tree that just needs pruning and one that needs to come down.
Start at the Ground: Roots and Root Collar
Most hazard assessments begin below the canopy, not above it, because root and trunk-base problems are the leading cause of sudden tree failure.
- Soil heaving or cracking in a ring around the trunk, especially on one side only — this often means the root plate is beginning to lift, a classic pre-failure sign after saturated soil from spring rain or a windstorm.
- Mushrooms, conks, or shelf fungus growing at the base of the trunk or directly over the roots. Fungus at ground level almost always means active wood decay underneath, even if the bark above looks intact.
- Exposed or severed roots from recent construction, trenching, or driveway work. Roots cut within a few feet of the trunk can compromise stability for years before the tree actually falls.
- Girdling roots that wrap around the trunk at the soil line instead of growing outward — common in trees planted too deep or left in a nursery pot too long.
Check the Lean
Some species, like river birch, naturally grow with a slight curve, so lean by itself isn’t automatically a red flag. What matters is whether the lean is new or worsening.
Signs a lean is actually dangerous:
- The lean appeared suddenly, or you can see fresh soil cracking on the side opposite the lean — a sign the root ball is actively tipping.
- The tree leans toward the house, driveway, or a spot where people regularly walk or park.
- The trunk curves upward partway through its height rather than growing straight — this usually means the lean developed slowly and the tree compensated over years, a different risk profile than a lean that appeared recently.
Look Up: Canopy Dieback and Deadwood
The canopy tells you how much of the tree is still functioning. A rough rule arborists use: if roughly 25% or more of the crown is dead or thinning, the tree is under significant stress and needs a closer look; above 50% dieback, removal is usually the safer call.
- Bare branches at the top of the canopy while lower limbs still have leaves (“stag-heading”) — often an early sign of root stress, drought, or disease working from the top down.
- Large dead limbs, bigger than 2-3 inches in diameter, hanging in the canopy, especially over a driveway, roof, or play area.
- Leaves that are smaller, sparser, or off-color compared to the same species elsewhere in the yard.
Cracks, Cavities, and Included Bark
These are the defects most likely to cause a sudden, catastrophic failure rather than a slow decline, which is why they get flagged as high priority.
- Vertical trunk cracks, particularly ones that run through both bark and visible wood — these indicate the trunk’s structural integrity is already compromised.
- Cavities or hollow sections you can see, or hear as a hollow thud rather than a solid knock when tapped, at the trunk base or in major limb unions.
- Included bark — a tight, V-shaped union where two major limbs meet with bark pinched between them instead of solid wood grain. These unions are weak and prone to splitting, especially under wind or ice load.
- Old wound scars or seams that haven’t closed over, particularly on the underside or leaning side of a limb.
The One-Person Rule
If you find one of these signs on its own — a little deadwood, one small mushroom at the base — it’s worth monitoring. If you find two or more together, such as a lean plus fungus at the base, or a crack plus canopy dieback, treat it as a priority and get it looked at before the next windstorm or heavy snow load, not after.
When to Stop Guessing and Call a Professional
A visual checklist gets you most of the way there, but it can’t tell you what’s happening inside the trunk or root system. If a tree checks two or more boxes above, or it’s tall enough to reach your house or a spot where people regularly pass underneath, it’s worth a professional assessment rather than a wait-and-see approach. Our crews evaluate hazard trees throughout Monroe County as part of routine tree removal consultations, and if a tree is salvageable, targeted pruning can sometimes resolve the risk without taking the whole tree down. For a deeper look at warning signs that tip a tree from “watch it” to “remove it,” see our guide on 8 signs a tree needs removal.
Frequently Asked Questions
Can a tree look completely healthy and still be hazardous?
Yes. Internal decay, root damage from construction, and girdling roots can all exist under a full, green canopy. That’s exactly why ground-level and trunk checks matter as much as looking at the leaves.
Is a leaning tree always dangerous?
Not always — some species and some old, established leans are stable. The real risk factor is a lean that’s new, worsening, or paired with soil cracking or heaving near the base, since that combination points to a root plate that’s actively shifting.
What does mushroom growth at the base of a tree actually mean?
Fungal fruiting bodies, including mushrooms, conks, and shelf fungus, at the trunk base are a visible sign of a much larger internal decay process. By the time you can see them, the decay has usually been progressing for a while.
How often should I walk my property and check for hazard signs?
A quick visual check twice a year, once in early spring after winter storms and once in fall before leaf drop, catches most developing problems while they’re still manageable.