You’ll whiles find a sapling which a territorial buck uses more than one season; the damage looks like it is historic. These territorial elders tend not to have to try too hard to impress, and more often than not they simply mark by rubbing their forehead or sub orbital gland on the tree as they pass, they only get a bit more emphatic when another animal of substantial stature poses an equal and persistent challenger, which is a rare occurrence. That’s also why it’s in your interests not to roll that fellow over from a sylvicultural viewpoint:
a) he uses the same tree/s on his rounds on his patch, thereby minimising losses overall, and
b) he keeps the young vandals away, all day every day; if he is removed, you can be sure that fraying damage will increase, sometimes severely if there are a number of competitors for his vacated patch.
Having said all this, it’s hard to be certain from the pictures supplied; I’ve also seen nibbling damage to ash by a vole living inside the dead grass within a tube which can also get out elsewhere from an ill-fitting tree tube. Voles are keen on young ash bark, I once lost around a hundred restocked 20/40 cm plants in just the couple of days before the tubes arrived on site.
It could be the early onset of Challara too, as
@mudman suggests
Then again, the cut stems in the second pic look like hare or sheep damage ( clean, diagonal bite), and when they aren’t eaten it’s usually a hare or hares doing the deed.