.They're like a wolf version of a dryad xD and it isn't uncommon to find moss growing on them (xD). basically their bones are not made of well bone they're made of wood and that's where the trees on the backs get their nutrients, the wolves' body. The tree acts a little like a "storing" system it stores up the extra energy and nutrients of the body and grows, in times of drought or in times of starvation the tree on it's back helps it stay alive. That's all I have worked out so far xD hope you like it.
EDIT: I messed up on the head -_- I always mess up on the head.
