What a failing tree looks like before it fails

Two things are worth saying before the list. First, a defect is not the same as a hazard: a tree with a cavity in the middle of a field is a tree with a cavity, while the same tree over a bedroom is a different conversation. Risk is always defect plus target. Second, almost nothing on this list is a verdict on its own. It is the combination, and particularly whether several defects line up on the same side of the tree, that matters.

Start at the ground

Soil cracking or heaving. Look at the ground on the side opposite any lean. A crescent of lifted or cracked soil, or a gap opening between the soil and the trunk base, means the root plate is moving. This is the most urgent finding on the whole list, and it is the one people walk past.

A missing root flare. A healthy trunk widens out where it meets the ground. A trunk that goes into the soil straight, like a post, usually means the tree was planted too deep or that soil or mulch has been piled against it since. Buried flares stay damp, rot slowly, and lose the structural taper the tree needs at its most loaded point.

Mushrooms and conks. Fungal fruiting bodies at the base or on surface roots indicate the fungus is already established in the wood, and the visible part is the last stage rather than the first. Not every conk means imminent failure, but a solid shelf fungus low on the trunk of a large tree over a house is worth having looked at rather than photographed and forgotten.

Cut roots. Where a trench, a driveway, a patio, or a utility line went in on one side of a trunk, the tree lost anchorage on that side even if it looks fine. On Piedmont clay, roots run wide and shallow, so a trench ten feet from the trunk can cut a significant share of the system. The roots guide covers what that does over time.

Then the trunk

Cavities and hollows. Hollowness alone is not a verdict. A tree carries most of its structural load in the outer wood, and a mature hardwood can lose a considerable proportion of its interior and remain sound for years. What matters is how much continuous shell remains around the circumference, and whether an opening interrupts it. A narrow slot up the side of a trunk is more concerning than a wide round hollow with sound wood all around it.

Seams and cracks. A vertical seam running up the trunk, particularly one that weeps or has callus rolled along both edges, indicates the wood has separated. Fresh cracks matter more than old ones the tree has been growing over for years.

Bulges and depressions. Trees add wood where they are stressed. A pronounced bulge often marks the point where a tree is compensating for internal decay, and a flat spot or depression on a normally round trunk sometimes marks where it has stopped being able to.

Missing bark. A strip of dead bark with the wood exposed behind it, particularly on the south or southwest face, is often old sun damage. It matters because it is a route in for decay, not because of the bark itself.

Then the unions

The place large limbs come off is where large limbs come off. Look at each major fork and ask two questions: are the two stems roughly the same thickness, and do they meet at a narrow angle. Two yeses is a codominant union, and if there is a dark seam running down between them rather than a raised ridge of wood, there is included bark in it. That means the two stems are pressed together rather than joined, and the union will open under load.

Included bark unions are worth acting on before they split, and often the action is reduction rather than removal: taking weight off the ends of both stems drops the load at the union substantially without losing the tree.

Then the crown

Deadwood. Dead limbs come down eventually, and they come down without warning because there is no living tissue left to bend. A few dead twigs in the interior of a large crown is normal shading. Substantial dead limbs scattered through the canopy is not.

Hangers. A limb broken but caught in the canopy is the single most commonly missed hazard on a property, because from a distance it looks like part of the tree. After any storm, look up.

Thinning from the top down. A crown that is losing density starting at the highest branches is the classic pattern of a tree in decline, whether the cause is root damage, drought stress, or disease. Thinning from the outside in on one section only is more likely to be localised, and often traces back to a specific damaged limb or root.

Epicormic sprouts. Clusters of thin vertical shoots erupting along a trunk or major limb are a stress response, generally to sudden light exposure or to the loss of a lot of canopy. They are the tree trying to rebuild leaf area quickly, and they are weakly attached.

The three findings that justify a call this week

• Ground cracked or lifted around the base. The root plate is moving.
• A lean that was not there before, or a lean that has visibly increased. A tree that has always leaned and grown to suit is a different matter entirely.
• A limb hung up in the canopy over anything you care about.

Things that look alarming and usually are not

• Ivy on the trunk. It competes and it hides defects from view, which is a real problem, but it is not itself a structural one.
• Lichen on bark. Lichen grows on healthy and unhealthy bark equally and tells you nothing about the tree.
• Sap or weeping in spring. Common in maples and some other species, and usually normal.
• Interior deadwood in a dense crown. Trees shed shaded branches as a matter of course.
• Surface roots in a lawn. Normal on Piedmont clay, where roots run shallow. Inconvenient, not dangerous, and cutting them to tidy the lawn is how a stable tree becomes an unstable one.