Help Please! What happened to my trees?!??! (pics included)

[friskyweasel]

hello -

I am clueless when it comes to gardening, but I recently noticed that the bark is literally GONE in several places on 2 of my back yard trees.

One of them is a small mimosa tree, and I think the other is a Japanese Maple. The Japanese Maple especially makes me sick...I really love that tree! In both cases, it happened some time this winter...I'm not sure when - I just noticed it one day on one of the trees, and then shortly thereafter noticed that BOTH trees were affected. To me it literally looks like someone "scraped" the bark off with a knife, or even like it was possibly "chewed" off. Sounds crazy, but that's what it looks like to my untrained eye.

Can someone look at these pics and give me any ideas about what this might be? Are my trees goners? Can they be saved?

Any input would be appreciated (see pics attached).

tia