Is My Tree Hazardous? Warning Signs and What to Do in Ottawa

A hazardous tree is one with a defect that makes it likely to fail, with something valuable or someone underneath it. The warning signs are dead or hanging limbs, cracks or splits in the trunk or forks, a sudden lean, heaved or lifted soil at the base, fungus or hollow areas in the trunk, and heavy decay. The risk is the defect combined with what is in the way: a tree in an empty field is not a hazard, while the same tree over a house is. If you spot these signs, tree removal or pruning from a professional crew is the safe way to deal with it.

Signs of a hazardous tree

Walk around the tree and look up, then down. These are the red flags arborists look for:

• Dead branches or a dead top. Dead wood is brittle and breaks without warning, especially under ice or wet snow.
• Hanging or broken limbs snagged in the crown after a storm.
• Cracks and splits in the trunk or where large limbs join it.
• Tight V-shaped forks, where two stems grow upward from one point with bark trapped between them. These are weak unions that split under load.
• Lean. Many trees lean gently and are stable. A tree that has started to lean recently, or leans over a building, is a concern.
• Lifted or cracked soil on one side of the trunk, which can mean the roots are letting go.
• Fungus growing on the trunk or at the base, which often signals decay.
• Cavities or hollows, and large wounds that are not closing.
• Roots that have been cut or damaged by trenching, driveway work or construction.
• A history of topping, where the main stems were cut back hard. The regrowth is weakly attached.

Why the target matters

Arborists talk about risk as three things together: how likely the tree is to fail, how likely the failure is to hit something, and how bad the damage would be. A tree with a decayed trunk in the back corner of a large lot is a different problem from one beside the driveway, the kids' play area or the bedroom wall.

That is why two trees with the same defect can get different advice. A tree might be left alone, pruned, monitored or removed depending on what is underneath it.

Ottawa weather and failures

Ottawa trees are tested by ice storms, wind, heavy wet snow and freeze and thaw cycles. Trees can fail in conditions that are not extreme if the tree already has a weakness. Ice and snow add weight to branches, and saturated soil makes it easier for a tree to tip.

For that reason, many people book a tree check in fall, before winter loading. With the leaves down, the branch structure is easier to see.

What to do if you think a tree is hazardous

1. Keep people and vehicles away from the area under the tree, especially in wind or storms.
2. Do not climb or cut it yourself if the problem is high up, large, or near a building or power line. Falling wood and tension in damaged limbs cause serious injuries.
3. Stay away from power lines. If a tree or branch is touching or near a line, call the utility, not a tree crew.
4. Take photos and note when you first saw the problem.
5. Have an arborist look at it. They can assess the risk and recommend pruning, support, monitoring or removal.
6. Check the permit rules before you remove a large tree. Many trees in Ottawa are protected under the City's Tree Protection By-law, so removal may need a permit unless an exemption applies.

If a tree has already fallen or a limb has come down on your property, our post on what to do when a tree falls in your yard covers the first steps.

Can a hazardous tree be saved?

Often, yes. Not every hazard means removal. Depending on the problem, an arborist may recommend:

• Pruning to remove dead or weak wood, as in crown cleaning.
• Reducing weight on a limb that is overextended.
• Cabling or bracing a weak union, where appropriate.
• Monitoring a tree with a minor defect over time.
• Removal when the tree is dead, badly decayed or leaning with root failure.

A tree with a failing root system, advanced trunk decay or a major split generally cannot be fixed.

Who is responsible?

This depends on where the tree stands. For a tree on your property, you are generally the one who has to deal with the risk. For a tree on City property, such as a street tree, contact the City of Ottawa. For a tree on a neighbour's property, start by talking to them and sharing your photos. If you are unsure about a legal question, ask a lawyer or your insurer, because we cannot give legal advice.

Frequently asked questions

How can I tell if a tree is about to fall?

You cannot always tell. Look for recent lean, lifted soil, cracks, dead wood, fungus and decay. If you see any of these on a tree near a building, have it assessed.

Is a leaning tree always dangerous?

No. Trees that have grown at an angle for years are often stable. A tree that has started to lean, or shows soil heaving at the base, is much more worrying.

Can I remove a hazardous tree without a permit in Ottawa?

It depends. The Tree Protection By-law protects distinctive trees on private property and has exemptions. Do not assume a risky tree is exempt. Read the permit guide or ask before removal.

What does a tree risk assessment involve?

An arborist looks at the tree's crown, trunk, roots and surroundings, notes defects, considers what is underneath, and recommends what to do.

Should I take action after a storm?

Check your trees from a safe distance after a storm. Dead and hanging limbs, new cracks or a changed lean are worth a call.

Need a risky tree dealt with?

Need tree removal in Ottawa? Call 613-627-2017 or get a free quote.

Sources

• Tree Protection By-law No. 2020-340 (City of Ottawa)
• ANSI A300 and ISA tree risk assessment guidance (International Society of Arboriculture)