Despite their dormant condition, trees and shrubs are exposed to and frequently endure many forms of damage during the winter, states David Robson, Extension Educator, University of Illinois Extension, Springfield Center. This is caused by rapidly changing temperatures which can kill living tissues beneath the bark. Usually the south side of the tree is affected due to the winter sun warming the bark. These are vertical separations of bark and wood and commonly occur on the south or southwest sides of trees.
Deciduous trees are more susceptible than evergreens.
This occurs primarily during periods of extreme and rapid fluctuations in temperatures. Spring flowering trees and shrubs, as well as peaches, nectarines and apricots, are susceptible. This causes most of the damage to evergreens such as pines, spruces, arborvitae, juniper and rhododendron. Evergreen plants lose water from their leaves even though they are dormant in the winter. This loss may be increased by drying winds or bright, sunny days.