1. The Tree Is Dead or Mostly Dead
A dead tree loses structural integrity quickly and can fall without warning — especially in wind or after rain saturates the soil around weakened roots. Look for:
- No leaf growth in spring (or sparse, off-season leaf drop)
- Branches that are brittle and snap easily
- Bark peeling off in large sheets
- A hollow sound when you knock on the trunk
What to do: Schedule removal promptly. Dead trees are cheaper per foot to remove than live trees in most cases, but they require more careful handling due to unpredictable structural failure.
2. Significant Trunk Damage or Cavities
Deep cracks, splits, large hollows, or extensive fungal growth on the trunk indicate internal decay. Not every cavity requires removal — trees can live with cavities for years if the damage is limited and the remaining wood is sound.
Rule of thumb: A cavity or decay affecting more than 30–40% of the trunk's cross-section is a significant structural risk. Get an arborist assessment; they can perform a resistance drill test to gauge internal integrity.
3. A Sudden or Significant Lean
Many trees develop a gradual lean toward available light over years — this is normal. What's dangerous is a sudden lean or one that has noticeably increased over a single season. This typically indicates root failure or a soil shift at the base.
Also watch for heaving or cracking soil near the base of the tree — a warning sign that the root plate is lifting.
4. Root Damage or Decay
Root problems are often invisible until the tree falls. Watch for these surface indicators:
- Mushrooms or bracket fungi growing from the base or soil around the tree
- Soft or spongy wood at the root collar (base of trunk)
- Soil heaving around the base
- Roots severed by recent construction, trenching, or pavement work
Root loss of more than 30–40% of a tree's root zone significantly increases fall risk. This is common after nearby excavation — trees in new construction zones are frequently destabilized.
5. Dead or Failing Branches Throughout the Canopy
A handful of dead branches can be pruned safely. When die-off extends through multiple major scaffold branches or the upper canopy, it signals systemic decline. Look for:
- "Dead topping" — the crown has no live branches
- Large hanging or broken branches ("widow makers") caught in the tree
- More than 30% of the canopy missing or dead
Hanging branches are an immediate hazard regardless of overall tree health. They should be removed as soon as they're identified.
6. Growing Into Power Lines or Structures
Trees in contact with power lines are a fire hazard and are regulated by most utility companies. Contact your utility before trimming near lines — in many areas, only authorized contractors can work within 10 feet of energized lines.
Trees touching your roof, foundation, or siding cause long-term structural damage and create a moisture pathway for rot and pests. Removal or major trimming is recommended before contact becomes entrenched.
7. Active Pest Infestation or Disease Spread
Some infestations and diseases kill trees quickly and have no effective treatment once advanced. Key ones to watch for in the US:
- Emerald Ash Borer — kills ash trees within 2–5 years of infestation
- Dutch Elm Disease — spreads through root grafts; removal slows spread
- Oak Wilt — spreads quickly through red oak species
- Thousand Cankers Disease — targets black walnut
Always consult a certified arborist for a diagnosis before deciding between removal and treatment. Treatment can be effective when disease is caught early.
When to Get an Arborist Assessment Instead of Removing
Not every problematic tree needs to come down. An ISA-certified arborist can assess:
- Whether cabling or bracing can stabilize a structurally weak tree
- Whether crown reduction removes enough weight to reduce failure risk
- Whether the disease is treatable and at what cost
Arborist assessments typically cost $75–$200 and can save you unnecessary removal costs.