My woods is absolutely full of black walnuts, many mature 50 year old trees, with most being in the 20-year old range. No noticeable loss of foliage. In fact I have many ferns and other native plants growing very close to the walnut trees. Since the walnuts are a native species, native plants typical don't have a problem with them. And, when they mature they will be worth a lot of money for logging.

I've always read not to plant mountain laurel within 50 feet of a black walnut tree.