Split tree trunk: can a cracked tree be saved?

Split tree trunk: cosmetic crack or structural failure?

Start with where the split stops. The USDA Forest Service risk manual defines a crack as a separation of the wood, a deep split through the bark into the wood, and says cracks form when the load is more than the stem can carry. Iowa State Extension’s test for normal bark cracking is what shows in the gap: healthy, developing bark and no exposed wood.

The ISA’s homeowner checklist asks two questions here: are there cracks or splits in the trunk or where branches attach, and does the tree have co-dominant stems, which the ISA also calls a split trunk and says can often be a failure point.

Sources: USDA Forest Service NA-TP-03-03; MSU Extension P3717; Iowa State Extension; WSU Extension; PNW Plant Disease Management Handbook. The “what to do” column is this site’s summary. Checked 2026-10-02.

Split in tree bark: frost cracks, sunscald and growth cracks

Most bark splits are cosmetic. As a trunk thickens, its outer bark dies and cracks; Iowa State Extension says normal cracking shows healthy new bark in the gap and no bare wood. Two winter injuries are worth a closer look.

Sunscald hits the south or southwest side of the trunk. On a sunny winter day the bark warms and loses its cold hardiness, then freezes fast when the sun drops; WSU Extension describes the result as an elongated patch of dead bark that dries, cracks and peels away from dead wood. Maples, lindens, mountain-ash, birch, flowering cherry and fruit trees are among the most susceptible, and young, thin-barked and newly planted trees most of all.

Frost cracks are vertical splits into the wood that open in a hard freeze. Iowa State Extension compares the sound to a shotgun and says the cracks usually close in the growing season but can reopen for years, and that trees can live with them. WSU Extension’s Marianne Ophardt adds the caution: frost cracks tend to start at an old wound, such as a flush cut, a topping cut or dead roots, and once wood fibers split they stay split, weakening that part of the trunk. A crack that keeps reopening under a raised rib of wood is what the Forest Service calls a ribbed crack, high risk when paired with another crack or extensive decay.

Both injuries need sun followed by hard cold, and east of the Cascades the cold is harder. In the USDA’s 2023 hardiness map, ZIP codes in Spokane, Yakima and Wenatchee sit in zone 7a and Bend in 6b, against 9a for downtown Seattle and 8b for Portland. Each half-zone is 5°F, so Spokane’s average coldest night of the year runs about 20°F colder than Seattle’s, and Bend’s about 25°F.

Tip: On young or newly planted trees, the PNW Plant Disease Management Handbook recommends a light-colored wrap from the soil line to the first branches, or a dilute whitewash; WSU Extension says to put wraps on in late fall, take them off in spring once hard frosts are past, and leave low branches to shade the trunk.

Japanese maples split and peel west of the Cascades too. Answering a Yamhill County homeowner in 2023, an OSU Extension Master Gardener named drought stress, sunscald and bacterial disease as the likely causes, noting that the Japanese maple is an understory tree and more susceptible to sun and heat; see Japanese maple care. Oaks are on UConn Extension’s list of trees prone to frost cracks, which most often form on the south or west side.

Co-dominant stems and included bark: why trunks split at the fork

The most common structural split starts at a fork. When two stems of about the same size grow from the same point at a narrow angle, the bark between them is pressed into the union. The Forest Service pruning guide calls this included bark: a wedge of inward-rolled bark that prevents a strong attachment and often causes a crack below where the stems meet. A strong union is U-shaped, with a branch bark ridge, the raised ridge of bark that forms in the crotch where branch and stem tissue grow against each other.

MSU Extension describes how a weak fork gets worse: co-dominant stems squeeze each other as they grow, rub when they move in wind, and the wound lets decay in. Its rating table puts a co-dominant stem with included bark at moderate risk, and co-dominant stems or weak unions with cracks or decay at high.

Bigleaf maple is the Northwest’s classic case. The Forest Service silvics manual describes open-grown trees with rounded crowns on short, branching boles, and stumps that resprout into clumps (up to 67 sprouts counted around one stump), which can leave several trunks rising from one base. MSU lists maples among the trees more prone to branch failure from weak joints or brittle wood. More on the species: bigleaf maple.

Ice adds the load. The Forest Service pruning guide notes that poorly attached branches can be broken off by wind and accumulated snow and ice, and every one of the 128 ice-storm reports NOAA logged in Washington and Oregon from 2016 to 2025 came in December, January or February.

On a young tree the fix is cheap. The Forest Service guide recommends keeping side branches under one-half to three-quarters of the trunk’s diameter, and slowing one co-dominant stem by removing some of its side branches so the other becomes dominant; MSU notes that a co-dominant stem is easily removed while the tree is young. See how to prune a tree.

Cracks that mean the trunk is failing

The Forest Service manual traces most cracks to wounds that did not close properly, weak unions splitting, or flush-cut pruning, and sorts them by shape:

MSU’s thresholds are a useful scale: a crack without decay is a moderate risk; a crack that is splitting, several cracks, or a crack with decay is high; any cracked branch over 4 inches in diameter is high; and a crack splitting a stem or branch in two is extreme. Alabama Extension adds that cracks running across a stem are especially dangerous, and names frost, fire, lightning and heavy snow or wind loads as causes. A split from a strike is covered in lightning-struck tree.

Can a split tree be saved? Cabling and bracing

Sometimes. Cabling and bracing fall under ANSI A300, the U.S. tree-care standard published by the Tree Care Industry Association, as supplemental support systems, a section that also covers guying and propping. Purdue Extension describes a cable as extra-high-strength steel strand attached to bolts drilled into the upper crown, and a brace as a threaded rod installed through a weak union or split crotch for more rigid support. Both are used on co-dominant stems with included bark, overextended limbs and split crotches.

What they cannot do matters as much. TCIA says supplemental supports “do not provide primary support to a tree” and need periodic inspection by an arborist. Purdue says they are not for trees in poor health or with decayed wood, that they are no guarantee against failure, and that they need a ground check every year and an arborist’s inspection every three years. And a cable does not close a crack: as WSU’s Ophardt notes, split wood fibers stay split.

Have the crack assessed before anyone drills into it, and ask whether reducing the weight on one stem, or removing it, would do the job instead. A tree risk assessment rates the crack against what the tree could hit; pruning options are on crown thinning and reduction, and what to look for in an arborist is on arborists.

When a split tree is an emergency

• A fresh split after a storm, at a fork or through the trunk, on a tree that can reach a house, road, car or path.
• A crack that is getting wider, or a stem that has started to pull away from its partner.
• A trunk splitting in two, or a split limb hanging in the crown. MSU rates both extreme.
• A horizontal crack across the grain, which the Forest Service treats as a sign of imminent failure.
• A split tree touching or near a power line. Call the utility, and never try to remove branches from or near a line (ISA). Only utility or qualified line-clearance crews work within 10 feet of lines (WAC 296-45; OAR 437-002-0306); see tree removal near power lines.

Until it is looked at, keep people, pets and cars out of the area the split part could reach. A tree that is actively failing is an emergency tree service call; a dead tree with cracks is covered in how to tell if a tree is dead.