Figure 9.  Proper pruning cut (left) and improper one (right) after six years on the same red oak.  Both branches were the same size.  No decay developed after the proper cut.  A large column of decay developed above and below the improper cut.  The large callus at right is not associated with development of decay.  Similar injuries in conifers include resin pockets, blue stain, cracks, and decay.