Cracks in a trunk or a leaning tree: what the sources say it may indicate

This page reports what the named sources say. It does not say whether any tree is safe or unsafe, or what should be done with it. Each source names a professional to ask: Alabama Extension a certified arborist, the Kentucky factsheet a forester or arborist, and ISA an ISA Certified Arborist.

What the Alabama Cooperative Extension System describes

The Alabama Extension Emergency Handbook article Caring for Trees: Post-Storm Assessment, dated December 11, 2018, starts from the target: it says a damaged tree that could fall on a home, road, parking lot or a much used patio or playground is a bigger concern than one in a rarely visited place. On lean, it says the worst storm injuries often happen below ground, and the most prominent sign of root failure is a leaning tree.

Sign in the article	Danger the article gives	What the article lists
Lean with mounded soil on the side opposite the lean	High	It says the mounding indicates broken and damaged roots and lists removal as the recommended maintenance.
Lean with soil cracks	Moderate	Assessment by a certified arborist.
Lean with no mounding or cracks	Low	Assessment by a certified arborist.
Horizontal crack on the main trunk	High	It calls these rare and hard to spot because of the bark, and lists removal.
Vertical crack on the main trunk	High	It calls these common after very high winds and lists removal.
Crack on a branch	Moderate	It lists pruning the branch to ISA standards.

The article also says to try to remember whether the lean existed before the storm, because a tree that has always leaned often has branches that grew toward the light. It says cracks are most common where branches or trunks join and that trees with cracks develop decay.

What University of Kentucky Extension describes

The University of Kentucky Cooperative Extension factsheet Identifying Hazard Trees (FORFS 17-02) says a tree is only a hazard if it could harm life or property. It says large cracks that reach through the bark into the wood, living or dead, should raise an immediate red flag, because they show the wood and tree beginning to fail. It says trees that lean are at greater risk of falling, and that trees with many branches from a single point, such as maples, elms and pears, are often prone to break at those weak unions. The factsheet says it does not replace professional help and names a forester or arborist.

What ISA describes

The ISA tree owner brochure Recognizing Tree Risk includes a checklist question about cracks or splits in the trunk or where branches attach. It says cracks or separations in the soil may point to roots moving, which it calls a warning sign especially if the tree is leaning, and that codominant stems (a split trunk) can often be failure points, and to watch for longitudinal cracks or splits on the trunk, major branches or branch unions. It says judging how serious a defect is is best done by a professional arborist, and that a tree with any of the defects should be examined by an ISA Certified Arborist. It lists pruning, cabling and bracing, routine care and removal as measures an arborist familiar with tree risk may suggest.

Where the sources agree

Alabama Extension and ISA both link a lean to damaged roots or moving soil under the tree, and Alabama Extension and the Kentucky factsheet both tie the concern to whether the tree could harm people or property. All three name an arborist (the Kentucky factsheet: a forester or arborist) as the person to ask. The guides on cracks, lean, tree risk assessment and whether a tree is safe report more from the trade side.

Who to call

ISA Find an Arborist: the ISA directory for an arborist who can examine a tree
Consulting arborists by country: the credentials and registers consulting arborists hold in each country
Tree down first steps: who the sources say to call when a tree has already fallen on a house, road or line