A young tree in my back yard, possibly an Akebono Cherry, has a damaged area on the trunk. What is the cause? What can be done? What is the prognosis? Thanks for your diagnosis and suggestions.
That looks like an old abiotic/mechanical injury. It is impossible to say exactly what, but this could include possibilities like lawnmower, bike, or other vehicle, guy wiring from staking, or even tying a dog out there. Something disrupted the bark in that area, and you can see the tree's attempt at healing itself by the new swollen-looking callouses growing on the outer edges.
There is nothing that you need to do.
The tree looks well otherwise. That area may not heal completely and will be a weak spot over time, but it also may grow out of it.
Keep the tree as healthy as possible and be sure to offer water if we were to enter a period of drought. You might consider gently removing the plants at the base of the tree and replanting them elsewhere. Then you could mulch the area and the tree would have less competition for water and nutrients. Mulch should only be 2-4 inches deep and should not be in direct contact with the trunk.