Signs a big tree may fall
The warning signs of a failing tree, from a new lean and heaving soil to conks, cracks and dead limbs, which trees break most, and what to do after a storm.
On this page
The signs, from the ground upWhat the tree could hitWhich trees break mostAfter a stormCalling an arboristCommon questionsSourcesMost of the signs that a big tree may fail can be seen from the ground, and the ones that matter most are at its base and in its biggest parts. Watch for a lean that is new or growing, soil heaved or cracked at the base, mushrooms or conks at the foot of the trunk, and cracks and cavities in the wood. A narrow fork with bark caught in it, large dead limbs and roots cut or buried by construction are the others. Whether to act depends on what the tree could hit.
The signs, from the ground up
Look at the roots and the base first, then the trunk and the crown.
At the base and the roots
- A new lean, or one that grows. A lean that formed over years, with a thickened lower trunk and branches sweeping upward, is a tree correcting itself. A lean that appeared suddenly, as after a storm, means the roots have partly failed.
- Heaved or cracked soil. Soil lifted or split on the side away from the lean shows the root plate rising, and a tree in that state is hard to anchor again.
- Mushrooms or conks at the base. Fruiting bodies at the foot of the trunk or on the roots mean decay in the wood that holds the tree up, as mushrooms at the base of a tree explains. Kretzschmaria, a fungus that looks like a black, charred crust at the base, rots the wood fast while the crown above can look healthy.
- Roots cut, buried or paved over. Construction, a change of grade, packed soil or new paving over the roots all raise the risk, and a tree short of roots blows over more easily.
A lean that is still growing needs an arborist now:
“Trees that continue to increase their lean angle over a short period of time or begin to show signs of soil upheaving should be considered high risk and inspected immediately by an arborist.” (University of Florida IFAS Extension, Is my tree safe? Recognizing Conditions that Increase the Likelihood of Tree Failure)
In the trunk and the crown
- Cracks and cavities. Long cracks or splits in the trunk, a big limb or a fork are where a tree breaks, and a cavity lets decay into the wood. How much a hollow weakens a trunk depends on the sound shell around it, as fungus is not a death sentence explains.
- A narrow fork with bark caught in it. Two stems of nearly equal size meeting in a tight V often trap bark between them, and they split more readily than a fork shaped like a U. Multistem or single stem shows how to spot one.
- Large dead or hanging limbs. A dead limb drops sooner or later, in calm weather as well as in storms, and big ones high in the crown are the worst. A broken limb still hanging is already failing.
- A thinning crown. Leaves that come out smaller or unusually yellow, and a crown that thins or dies back over the years, can mean the roots are failing, as in a tree dying from the top down.
What the tree could hit
Every tree can fall, but only a small number ever hit something or someone. What lies within reach decides what to do. A big dead limb high over a roof, a drive or a bench matters more than the same limb over an empty corner, and a limb that falls from high up lands harder. Where the target can move, move it:
“While a home or a nearby power line cannot be moved, it is possible to move picnic tables, cars, landscape features, or other possible targets to prevent them from being hit by a falling tree.” (International Society of Arboriculture, Managing Hazards and Risk)
A tree with nothing beneath it can be left to stand, and a hollow one is habitat for owls, bats and bees. A tree that could reach a power line is the power company’s to deal with, never a homeowner’s.
Which trees break most
Fast-growing trees with weak wood break most. Silver maple, eastern cottonwood and the willows are weak-wooded and prone to storm damage. We do not grow silver maple, eastern cottonwood or black willow. In a University of Florida survey of 85 arborists, urban foresters and scientists, more than half rated silver maple and Bradford pear low in wind resistance. Every one who rated white oak or mockernut hickory put it high or medium.
Hickories and white oak resist ice as well, as the tables in ice and snow damage on trees show. Silver maple, the willows and Bradford pear are also among the trees not to plant near a house. Any tree fails more readily once it is stressed, since branches often break where disease or insects have already weakened the wood.
After a storm
Look before you touch anything:
- Power lines. Keep away from any tree or limb near a line, even with the power off, and call the utility.
- Big trees and limbs. Leave a large tree or limb, or one lying on a house or a car, to a professional, since it can weigh thousands of pounds and shift as it is cut.
- A new lean. A lean that appeared in the storm means the roots partly failed, and it needs attention at once. A small tree with an unbroken trunk can be pulled upright and held with lines set slack.
- No topping. Cutting a tree back to stubs to make it safer for the next storm does the opposite in the long run.
Calling an arborist
An arborist trained in tree risk assessment weighs how likely a tree or a limb is to fail against what it would hit. The International Society of Arboriculture grants a Tree Risk Assessment Qualification for that work. The arborist may move the target, prune out the defective limbs, cable and brace weak stems, or remove the tree. Cables and braces are no guarantee against failure.
Have big trees near a house looked at every few years. The society’s Find an Arborist and Verify a Credential tools at TreesAreGood.org find a certified arborist near you and check the credential. Blue Whale Trees answers questions about a tree you already have through its support page. A photo of the whole tree, a close-up of the base or the crack and a note on when it changed help us answer quickly.
Common questions
How can you tell if a tree is going to fall?
Look for a lean that is new or growing, soil heaved or cracked at the base, mushrooms or conks at the foot of the trunk, long cracks, and large dead limbs. A tree with any of these over a house or a drive needs an arborist’s look.
Is a leaning tree dangerous?
A lean the tree grew into over years, with a thickened lower trunk and upturned branches, usually is not. A lean that appeared suddenly or keeps growing, or soil heaving at the base, means the roots are failing.
Do mushrooms at the base of a tree mean it will fall?
Not always, but mushrooms or conks at the base or on the roots mean decay in the wood that holds the tree up. Have the tree looked at if it stands over anything it could hit.
Which trees are most likely to fall in a storm?
Fast-growing, weak-wooded trees such as silver maple, cottonwood and the willows, and Bradford pear with its weak forks. Any tree that is stressed, decayed or short of roots fails more readily.
Sources
(5 references)
- Is my tree safe? Recognizing Conditions that Increase the Likelihood of Tree Failure: University of Florida IFAS Extension (Drew C. McLean, Andrew K. Koeser, Robert J. Northrop and Gitta Hasing, EP507), with its publication Selecting Coastal Plain Species for Wind Resistance (FR174): dead and hanging limbs, codominant stems and included bark, conks and cavities, slow leans against sudden ones, the quotation, a thinning crown and buried or girdled roots; the survey of 85 experts rating silver maple, Bradford pear, white oak and mockernut hickory for wind resistance.
- Managing Hazards and Risk: International Society of Arboriculture, TreesAreGood.org, with its brochure Recognizing Tree Risk and the society’s page Types of Credentials: the quotation on moving the target, pruning, cabling and bracing that guarantee nothing, and removal; few falling trees hitting anything, heaving soil, cracks and splits, construction, grade changes and paving, small or yellow leaves, power lines, the Find an Arborist and Verify a Credential tools, and the Tree Risk Assessment Qualification.
- What to Do About Leaning Trees: Penn State Extension (Brian Wolyniak), with its page Helping Trees Recover After Storms: soil heaved on the back side of a lean, a tree hard to anchor again, small trees righted with lines set without tension; power lines even with the power off, topping that makes a tree less safe in the long run, and risk assessment by a TRAQ-qualified arborist.
- Kretzschmaria Basal Canker: Fast Path to Tree Failure: Purdue Landscape Report: the charred crust at the base, decay of both lignin and cellulose, and a crown that can look healthy.
- Tree Care Before and After Storms: The Morton Arboretum, with its pages Tree Root Problems, Silver maple, Eastern cottonwood and Black willow: inspections every few years, stressed trees failing more readily and branches breaking where disease or insects weakened the wood, large trees and limbs left to professionals, and power lines; roots cut short and trees blown over more easily; silver maple, cottonwood and the willows as weak-wooded trees.
