In the northern United States and Canada, in the months of January, February or March, on sunny days sap can rise from the roots, upward, into the trunk of the tree. If this warm period is followed by a dramatic drop in temperature the sap can be trapped and freeze. This expansion can cause vertical cracks in the bark, or wood. This is usually seen on thin or smooth barked trees.
Wrapping as a Prevention
Wrapping refers to the technique of winding a crepe-type paper or plastic material around the barks of tree trunks. Generally speaking, this is needed during the first few winters after planting. Commercial tree-wrap is sold at nurseries and in garden-supply stores. To wrap a tree, start at the bottom and wind the paper around the tree to the level of the second branch. Fasten the paper at the top with a tack. Don’t forget to remove the wrapping each spring to prevent moisture buildup, disease and insect infestation.
Clark's Tree Wrap is a good product. You can buy a roll online or occasionally find it at Farm & Fleet, Jung's garden center, or maybe your local hardware store.