Can I plant Serviceberry, Bayberry, and/or Winterberry shrubs underneath Black Walnut Trees? I've found conflicting information on Serviceberry and Winterberry and no information at all about Bayberry.
Try searching under Permaculture, they talk about Guilds or what plants will grow and promote the growth of other plants and trees.
The Virginia Coop. Ext. Serv. used to have a publication titled "What grows under black walnuts?" cited above. Unfortunately, the link no longer works.
Try to contact them directly or use the Wayback Machine.
You can plant whatever you want under black walnuts. The question is, what will survive/thrive in this location.
Sorry couldn't resist. You'll just have to find the best listng on this topic that you can, and then experiment.