Cracks in trees: what the standards and agencies describe

This page describes what published sources say about one structural condition in trees. It gives no verdict on any tree and is not an assessment. The sources come from the United States and the United Kingdom. The parent page, structural defects in trees, compares the conditions that have pages here.

What the sources describe

The US Forest Service brochure defines a crack as a deep split through the bark that extends into the wood, and says cracks are extremely dangerous because they show the tree is already failing. Its list of reasons to act names a crack that extends deeply into or completely through the stem, two or more cracks in the same general area of the stem, a crack in contact with another defect, and a crack in a branch big enough to cause injury.

The Illinois Extension article describes cracks as weak areas and lists causes: bending or twisting, growth expansion, frost cracking, bark inclusion, or stem girdling roots. It says immediate action is warranted where two or more cracks occur in the same area or where splits through the bark extend into the wood. The University of Kentucky leaflet says large cracks that go into and below the bark, into living or dead wood, should raise immediate red flags and show that the wood is beginning to fail.

Other lists

ISA Trees Are Good: item E of its list is cracks or splits, longitudinal on the trunk, major branches or branch unions. Its checklist asks about cracks or splits in the trunk or where branches attach. Item B says cracks or separations in the soil may indicate soil heaving from excessive root movement, especially if the tree is leaning.
National Tree Safety Group: lists splitting, bark and wood fractures and soil cracks among the signs that might indicate a structural defect, although not necessarily a hazardous one.

Where the sources add a caution

The National Tree Safety Group guidance defines a defect as a condition that predisposes a tree or part of it to structural failure, and says not every unusual feature is one. A crack is a description of what is on the tree, not a finding about how it will behave. The US Forest Service brochure adds that a defect matters where a target, such as a person or property, is within striking distance of the tree. The Illinois article is a news release dated June 19, 2023, and the ISA leaflet is the 2021 edition. The sources were written for different readers and do not use one shared list, so the same condition can sit under different headings.

Who looks at this

For the methods and the credentials, see tree risk assessment methods and consulting arborist credentials. Related conditions are on codominant stems and included bark.