Walnut, Black Growth
Foresters have an instrument called a tree ring borer. it is a hollow drill that is screwed into the tree creating less than a 3/8 inch hole in the tree. a 1/8 tree core is extracted and the hollow drill is extracted. The forester can clean up the core with sand paper or a razer blade and count the rings from the bark to the pith. this is the least invasive means of aging a tree. the wound should seal over in 2-3 years and the tree should be fine.