Trees Can Get Sunburned

While we might associate sunburn with summer beach days, trees face a similar danger in the dead of winter (Review). Known as sunscald, this condition primarily affects young, thin-barked trees like maples, lindens, and fruit trees. The damage typically occurs on the south or southwest side of the trunk, where the low-angled winter sun provides intense, direct warmth. This is especially risky for newly planted trees or those that have suddenly lost the shade of a neighboring structure or tree, leaving their sensitive bark exposed to the elements for the first time.

The mechanism behind sunscald is a dramatic day-to-night temperature swing. During a sunny winter afternoon, solar radiation can heat the bark enough to awaken dormant cells in the living tissue just beneath it, called the cambium. These active cells are full of water. When night falls and temperatures plummet below freezing, this water expands into ice crystals, rupturing and killing the cells. The result is a patch of dead tissue