I believe that is a grafted cherry. If you look at the branches around the graft, if you see 1/8" diameter holes, it probable that you have tortrix (bug). The female chews into the bark to the cambium, lays her eggs, and the larvae chew around the cambium, girdling the branch.
If you don't have that, there are several other insects, fungi (I saw some shothole), rusts and bacteria that attack those trees. Or it could be that the tree decided to kill off that branch because it wasn't producing enough photosynthate.
From the pics, the crown doesn't look that bad as a whole. Don't let it get drought stressed in the summer. A thin layer of mulch wouldn't hurt either.
