Signs a Tree Is Dead or Dangerous

1. "Dangerous" means it could hit something

• Defect plus target. The USDA Forest Service defines a hazard tree as one with structural defects likely to cause all or part of it to fail and strike a "target": a vehicle, a building or a place where people gather, like a street or backyard. A defective tree isn't a hazard unless part of it is within striking distance of a target.
• What's underneath matters. UT Extension says a tree leaning over a bedroom is the most hazardous case, and trees near high-use areas carry more risk than those near places people rarely go.
• Green leaves don't prove it's safe. The Forest Service says trunks and branches can be quite defective and still support a lush green crown.

Source: USDA Forest Service NA-FR-01-96, How to Recognize Hazardous Defects in Trees (PDF)

Source: UT Extension SP 573, How to Recognize and Prevent Tree Hazards (PDF)

3. Warning signs in the crown and branches

• Dieback from the top down. UT Extension says upper-crown branches often die from the top down in response to stress such as repeated insect defoliation, drought, soil compaction or root disease. Trees can recover if the stress is removed in time, but trees in advanced crown decline will die and should be removed.
• Dead branches only on one side. UMD Extension says this can be a symptom of root or trunk damage on that side and should be looked at by an arborist.
• Weak V-shaped forks. UT Extension says V-shaped forks are weaker than wider-angled ones and often fail in ice storms, heavy wet snow or high winds; elm, oak, maple, yellow-poplar and willow are especially prone. The Forest Service adds that bark trapped inside a tight union makes it much weaker.
• Sprouts from the base or trunk. UMD Extension says clusters of sprouts or small shoots along the trunk are a response to severe stress.
• Lots of damage overall. UMD Extension says a tree with 50% of the tree damaged probably should be removed.

Source: UT Extension SP 573, How to Recognize and Prevent Tree Hazards (PDF)

Source: University of Maryland Extension, How Do You Decide When to Remove a Tree?

Source: USDA Forest Service NA-FR-01-96, How to Recognize Hazardous Defects in Trees (PDF)

5. Roots and lean

• Root problems can drop a tree on a calm day. The Forest Service says trees with root problems may blow over in storms or even fall without warning in summer under the weight of their leaves. UT Extension notes some trees fall on a perfectly still day.
• A new lean with lifted soil. Act if a tree is leaning with recently exposed roots, soil movement or soil mounding at the base, per the Forest Service. UT Extension says uplifted soil on the side opposite the lean is a clue the lean is recent, and trees that grew leaning are less hazardous than straight trees that developed a lean.
• Too much lean. UT Extension says trees that lean more than 15 degrees from vertical generally should be removed. UMD Extension says a sudden lean means the roots have broken or weakened and the tree should probably be removed immediately.
• Cut or crushed roots. Construction, trenching, paving and driving over roots all damage them. The Forest Service flags trees where more than half the roots under the crown have been cut or crushed; UT Extension says a tree with half its root system damaged should probably be removed, and that problems can show up years after construction ends.
• Above-ground clues. UT Extension lists thin crowns, small or yellowing leaves, stunted growth, soil fill around the tree and discolored wood at the root collar as signs of poor roots. Trees in shallow, wet soils are more prone to uprooting.

Source: USDA Forest Service NA-FR-01-96, How to Recognize Hazardous Defects in Trees (PDF)

Source: UT Extension SP 573, How to Recognize and Prevent Tree Hazards (PDF)

Source: University of Maryland Extension, How Do You Decide When to Remove a Tree?

7. What to do about it

• Inspect on a schedule. UT Extension recommends at least one inspection a year and ideally two, one in summer with leaves on and one in winter. The Forest Service adds an inspection after severe storms; see after a storm.
• Look from every side. Walk all the way around the tree, check from the roots up, and use binoculars for high branches.
• Three ways to fix a hazard. The Forest Service lists moving the target (a swing set, a parked car), pruning the defective branch, or removing the tree. It calls removal the final option and says removing hazard trees is inherently dangerous and usually a job for a professional arborist.
• Skip topping. The Forest Service says topping and tipping are harmful and should never be used, because the stubs decay and create weak new branches.
• Ask a qualified person. UT Extension says to contact your county Extension agent or a tree professional when in doubt. UK Extension suggests an arborist certified through the International Society of Arboriculture.
• Near a power line? Don't prune it yourself. University of Maryland Extension says limb removal anywhere near power lines is never a homeowner job; if you're a KUB customer, call KUB at 865-524-2911 for downed or threatened lines. See trees near power lines for what KUB handles and what falls to you.
• Check the rules before cutting. Knoxville's city code says no one may remove a tree on city property without the Urban Forester's written approval. See the permit guide for your area.

Source: UT Extension SP 573, How to Recognize and Prevent Tree Hazards (PDF)

Source: USDA Forest Service NA-FR-01-96, How to Recognize Hazardous Defects in Trees (PDF)

Source: University of Kentucky Cooperative Extension FORFS 17-02, Identifying Hazard Trees (PDF)

Source: University of Maryland Extension, How Do You Decide When to Remove a Tree?

Source: KUB, Who's Responsible for Tree Work When the Electric Lines to Your House Are Damaged? (PDF)

Source: Knoxville City Code, Chapter 14 (Trees), City-hosted copy