We had a black walnut tree that was dropping walnuts on our roof last year; so we took it down this week. Any idea what caused the ring of small circles around the center dark ring? It is on the main trunk, but not at the base of the stump and not at side branches. Two lowest sections (approx 8’ each) do not have small dots; central leader does. Doesn’t seem like side branches do. I have a section if interested. Wood is still on property; although neighbor plans to pick up in a couple days. Thank you!