We do not often think of animals having odd habits but all species DO. Horses will "crib". Cats will eat yarn or wool bits. Dogs have a variety of odd habits--can't break them of them. If she has been doing this for so long, providing a substitute would doubtless not change her pleasure of wood in a special place. Maybe it started with something delightfully edible on those spots--at some time? If she has no problems, not to worry!!! But it IS interesting!