A lab dog is standing on a fallen tree trunk with a guy in the background.
the animal is sitting under tree
A dog cannot be standing on a fallen tree trunk and sitting under a tree simultaneously.  One cannot sit under a fallen tree.
An animal is not necessarily a lab dog. If the dog is standing, then it is not sitting. If the dog is on a fallen tree, then it is not under the tree.
A dog cannot be standing on a fallen tree trunk and also sitting at the same time. Also, the tree must either be fallen or standing.