I have never in my life seen or heard of a dog doing this. When I called the Vet he said that it is probably because she is still a puppy. She is about 10 months old now & has been doing it for a few months. I've searched the web but haven't found any information about dogs doing this. A friend of mine has horses & she said that horses do this because of something lacking in their nutrition so she suggested that I buy a horse block. Well I did but our dog is still chewing on the trees. She has totally destroyed/killed at least 1 tree and possibly more. We have many trees in our yard and she has chewed on almost all of them. You can actually see the marks on the trees where she has been chewing. Has anyone had this problem and if so what was done to fix it?? I love my GSD to death, but I cannot have her killing all of our trees. I don't know what to do. Is there something that I can put on my trees that would deter her?? Please help or give any opinions. Thanks.