After a chilly winter night, the south- and east-facing sides of a cherry tree may split as the morning sun causes the thin bark to warm, expand and break. The tree should heal on its own, forming callused scabs. Do not paint or try to seal a split with paint or tar; this provides no help and may even make matters worse. This spring and summer keep the stress on the tree to a minimum and water it when we get another dry spell. If you like, you can erect a sun barrier for the winter on the southwest side of the trunk of the tree if it is in a really exposed location

For more information about bark splitting in cherry trees, see

http://plantclinic.cornell.edu/factsheets/barksplitting.pdf