Although young trees can tolerate partial shade, butternut must be in
the overstory to thrive and is classified as intolerant to shade and
competition . Like other members of the Junglandaceae family,
butternut produces a substance called juglone, a naphthoquinone that is
selectively toxic to associated vegetation. Greatest concentrations of
juglone are in root tissue and fruit husks, with lesser amounts in the
leaves, catkins, buds, and inner bark .
- 11. George, David W.; Fischer, Burnell C. 1989. The effect of site and age on tree regeneration in young upland hardwood clearcuts. In: Rink, George; Budelsky, Carl A., eds. Proceedings, 7th central hardwood conference; 1989 March 5-8; Carbondale, IL. Gen. Tech. Rep. NC-132. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 40-47. 
- 24. Rink, George. 1990. Juglans cinera L. Butternut. In: Burns, Russell M.; Honkala, Barbara H., technical coordinators. Silvics of North America. Vol. 2. Hardwoods. Agric. Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest Service: 386-390. 
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