Juglans cinerea achieves optimal growth on well-drained soils of bottomlands and floodplains, but rarely occurs in pure stands. According to Rink (1990), this species grows best in riparian sites and well-drained soils, but is seldom found on dry, compact, or infertile soils. Rink also notes that butternut is found at much higher elevations (up to 4900 ft) in the Virginias than black walnut. Butternut is shade-intolerant, growing best in full sunlight. Young trees can tolerate some competition from the side, but will not withstand shade from above. This species needs to be in the canopy in order to survive. Reproduction is successful only in areas where shade does not inhibit its growth, such as stand openings or in fields (Skilling 1993, Ostry et al. 1994).
This species is being seriously impacted, if not devastated, by a canker fungus (Sirococcus clavigignenti-juglandacearum) that is spreading rapidly throughout its range, and few stands remain uninfected. The origin of the disease is unknown, although Fogelson and Campbell (1990) believe it may have been introduced about 40 years ago on the east coast of the United States. According to Anderson (1993), 40- year-old cankers have been observed in North Carolina. Long noted as suffering from a canker dieback (frequently called "butternut decline"), scientists from Wisconsin first identified the disease agent as a new species of Sirococcus in 1967, although tests of trees in North Carolina demonstrated its presence there in 1952. This disease has spread quickly (within 30 years) throughout butternut's range, infecting and killing trees in all locations. In the Great Lakes states, all sites examined by researchers had been infected with canker. The disease vectors are poorly known, but the canker is believed to be transmitted at least in part by raindrops splashing spores from infected trees onto healthy ones, and possibly via insects. If the spores become airborne, they are able to be dispersed over great distances. The spores are produced throughout the growing season and can survive when weather conditions are cool and skies are overcast. (Kuntz et al. 1979, Fogelson and Campbell 1990, Forest Service News 1992, Ostry et al. 1994).
Symptoms of the disease include the appearance of lens-shaped cankers on the trunk, limbs, twigs, and immature nut of the tree. In spring, an inky-black, thin fluid is exuded from the cankers. These cankers usually continue to grow in size and girdle the tree, eventually killing it by destroying the cambium. The girdling of the tree often causes a wilting of the leaves, especially noticeable in the crown (Fogelson and Campbell 1990). Trees with reduced vigor become susceptible to insects and secondary disease agents, particularly Melanconis juglandis (E. and E.) Graves, which causes branch dieback (Skilling 1993).
Butternut is an important source of mast for wildlife, especially in the northern part of its range, where black walnut (Juglans nigra) does not occur. Squirrels and other rodents are some of the consumers of the seeds. (Ostry et al. 1994).
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