Tree Risk Self-Check: Spot the Warning Signs

What are the warning signs a tree could break?

The signs arborists take most seriously are cracks, broken branches hanging in the tree, a new lean with soil lifting at the base, and mushrooms or conks on the trunk or big roots. Dead branches, hollow spots and tight V-shaped forks matter too, mostly when the tree could hit something.

Look from a safe distance. Don’t climb the tree or go near wires. If a tree touches or leans on a power line, stay away from the tree and the line, and call your electric utility.

Why does what’s under the tree matter so much?

Risk is not only about the tree. The same weak branch is a very different situation over an empty lawn than over a bedroom, a driveway or a swing set.

Arborists rate tree risk with a method from the International Society of Arboriculture (ISA). For each part of a tree, it weighs three things:

1. The chance the part could break in the next few years.
2. The chance it could hit something, like a house, a car or people. Look at anything within about one tree-height of the trunk. A whole tree can reach that far if it tips over.
3. How much harm it could do if it hit.

The self-check above follows those steps in a simple form. It gives a possible level: Lower, Moderate, Elevated or Highly elevated. It uses only your answers, and it is not made or endorsed by ISA.

Are V-shaped forks a problem?

They can be. When two stems of about the same size grow up in a tight V, bark can get pinched inside the joint, and that joint can be weaker than a single trunk or a wide, U-shaped fork.

Purdue Extension calls these forks (codominant stems) the most common risk of tree failure, and says the longer the stems grow, the more likely a split. University of Minnesota storm surveys, cited by the Tree Care Industry Association, found that 21% of failed yard trees broke at forks like these.

Look for a tight V instead of a U, a line of bark pinched down into the joint, and any seam, bulge or crack below it.

What if there’s a crack below the fork?

A crack at or below a tight V-fork can be a sign the joint has started to split. Consider keeping people and cars out from under it, and have an arborist look as soon as you can. In the self-check, a crack plus a tight V-fork gives the highest chance of a break for that part of the tree. Don’t wrap chain or wire around the stems, and don’t try to bolt it yourself.

Can cabling and bracing help a weak fork?

Often, yes, if the tree is healthy enough. Cabling and bracing support a weak fork so the stems can’t spread apart as far in wind, ice or snow.

• Cabling: strong, flexible steel cables (or a rope system) set high in the crown to link the stems and limit how far they move.
• Bracing: threaded steel rods through a weak joint. Bracing can also help hold a fork that has already split.
• Pruning: shortening or lightening one stem lowers the load. On young trees, early pruning to one main stem can keep the problem from forming.

Support systems can lower the chance of a split, but they are not a guarantee against failure. Not every tree is a good fit, since decay or root problems can change the answer. The best time to ask is before a crack forms, while there are more options.

Our arborists install cabling and bracing to ANSI A300 standards, and we recommend a yearly check of every system. We install both dynamic (Cobra) and static cabling and bracing systems.

What does a professional tree risk assessment include?

A trained arborist looks at the whole tree, the site and everything the tree could hit, then rates the risk and gives you options to lower it. Our TRAQ-qualified arborists (ISA Tree Risk Assessment Qualified) use the ISA method and work to ANSI A300 standards.

A typical assessment covers:

• The site: what’s under the tree, how often people are there, the soil and wind, and any recent digging or building.
• The tree, from roots to crown: the root collar, trunk, forks, branches and signs of decay. Most trees get a full walk-around look from the ground. When a closer look is needed, we use advanced decay testing, like resistance drilling and sound tomography. The report afterward includes a 3D, MRI-style model of the inside of the tree.
• A rating and options: for each concern, options can include pruning, cabling or bracing, moving what’s underneath (like a swing set or a parking spot), checking again later, or removal.
• A time frame: a rating covers a set period, often 1 to 5 years, so trees should be checked again.

When you need it in writing, for an HOA, a permit or a home sale, our arborists can write an arborist report.

When should I call an arborist?

It’s worth calling soon if you see a crack, a hanging broken branch, a new lean, lifting soil or mushrooms at the base, and the tree could hit a house, car, path, play area or power line. With no warning signs, a check every few years and after big storms is a good habit.

Any tree can break, even with no warning signs. Virginia Cooperative Extension suggests having an arborist check your trees every 3 or 4 years.

What not to do:

• Climb a tree that has a crack or a hanging branch.
• Cut a split or leaning tree yourself. Wood under strain can move without warning.
• Pull a leaning tree straight, or prop it up yourself.
• Wrap chain or wire around the stems.