Sunscald, frost cracking of overexposed forest tree stems possible with freezing winter conditions

Mike Schira, Michigan State University Extension - December 18, 2012

Trees growing on the edges and in openings of forest stands are susceptible to sunscald and frost cracking on sunny winter days. This damage can reduce commercial value as well as exposing trees to further insect and disease damage.

Frozen trees in winter season dormancy with southwest exposure to the sun are susceptible to sunscald damage and frost cracking on sunny days. Afternoon sun on the trunks of trees can thaw and activate dormant tree cells. A quick freeze once the sun is gone will kill the cells and create dead patches in the bark referred to as sunscald. Sometimes the sun’s thawing/freezing action will cause a similar problem with only a split or seam in the bark called frost cracking.

Thinner bark species including maples, basswood and ash, among others, are susceptible to this seasonal damage along with young exposed seedlings of many species. Although healthy trees will survive the injury by walling off the damaged area once growing season resumes, it can result in scarring, dead patches on the trunks that reduce merchantable value of forest trees.

This sunscald activity can also expose damaged areas to insect and disease agents, further damaging the trees. Making adjustments through management planning in conjunction with timber harvest activities can help reduce the negative impacts from these seasonal events. Over-thinning of stands or creating too large of openings can create conditions favorable to sunscald-type damage. Michigan State University Extension Tree Series Bulletin E 2769 Northern Hardwood Forest Management is a resource of helpful management suggestions.

Consider leaving trees that have already been damaged along the edges of forested areas. These trees provide protection to the stands. Removal of edge trees will simply expose the next line of stems to potential sunscald damage. MSU Extension does not recommend the use of wound dressing on the species most susceptible to this kind of damage.

Healthy trees should continue to grow through the damage. In forested situations consider encouraging shrub and conifer species establishment to help protect the lower stems of susceptible trees. This lower vegetation may also help promote more favorable wildlife conditions in your forested stands.

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