I wouldn't say impossible, its been proven in a few pen raised deer, that some bucks NEVER shed there antlers, EXTREMELY RARE, but its can happen

some pictures might help us , give better idea's on what made the marks
never seen bears use saplings, they tend to use larger tree's and scratch up high to
they will use smaller tree's to scratch themselves, but
my guess might be a porcupine , they will eat bark off tree's?
any chance of posting some pic's ??