Shredding of bark on maples (Japanese in particular) in spring in the PNW is often attributed to squirrels - unfortunately, a very common problem here. They strip the very thin and tender bark for nesting material. Wrapping loosely with chicken wire is a good deterrent or you could try the tree wrap product that you coat with something like Tanglefoot. This tends to be a very seasonal problem, so either way, it is something you could remove later in the season.

Thanks gardengal. In desperation last night, I cut up small pieces of bubble wrap and very loosely wrapped that around the affected areas figuring the squirrels would "buzz off" when they heard the bubbles burst. Do you think it's ok to leave the bubblewrap in place, or might it encourage fungal growth?

Bubble wrap or anything else that is impervious to moisture and impedes air flow would not be my first choice.