That's merely my family's name for these gnarled, dead trees near the (disused?) visitor centre, but I wouldn't be surprised if others share the fantasy.
My own invented interpretation is that they're a balanced pair; one 'good' witch/tree watching and restraining one 'bad' witch/tree. My mother thinks they're both 'evil', and though she normally likes to feel the texture of tree bark, she won't touch these trees, considering them too sinister.