It appears that sapsuckers have fed on your tree. Unlike other woodpeckers, sapsuckers are not primarily interested in insects for food. Instead, they're looking for tree sap. They collect sap using their long brush- tipped tongue as the sap flows out of the holes they've drilled. The holes sapsuckers drill are evenly spaced up and down and around the trunk, appearing as if done by a machine. In most cases, sapsuckers do not seriously harm trees. The holes are shallow and the wounds do not cause significant or permanent damage. But sometimes a particular tree becomes a favorite feeding place for an individual sapsucker. In this case, large areas on the trunk may be dotted with many holes. When this happens, the tree may be weakened and become more sensitive to other problems, such as disease or drought. The wounds themselves may attract harmful insects. To control sapsucker damage, wrap the area of the trunk where the bird is drilling with burlap or hardware cloth. Scare the bird away as often as possible when you discover it drilling. Sometimes placing an artificial owl or snake or a bright shiny object in the tree may *temporarily* frighten it away. Be prepared, however, for the bird to simply move up the tree truck to an uncovered portion. Both state and federal laws protect yellow-bellied sapsuckers and other woodpeckers.

Washington State University has a publication, Recognizing Sapsucker Damage, you might find of interest. It's at http://cru.cahe.wsu.edu/CEPublications/FS057E/FS057E.pdf