Stewardship Overview: Butternut is shade-intolerant, achieving its best growth in full sunlight and requires some form of disturbance, such as soil disturbance and the creation of canopy gaps for successful reproduction and establishment (Skilling 1993).
This species is critically threatened by the rapid spread of a canker fungus (Sirococcus clavigignenti-juglandacearum), which is killing trees (including sprouts and seedlings) throughout its range (Ostry et al. 1994). A majority of trees throughout the range may be infected with butternut canker, and recovery will be difficult. Many stands of butternut trees have been seriously impacted, leaving small clusters of very vulnerable individuals. The range of infection has apparently increased dramatically in recent time. For example, 77 percent of the trees have died in North Carolina and Virginia (Anderson 1993). A treatment with no known value (Skilling 1993) is the culling of infected trees to attempt to prevent the spread of the disease to other individuals within a stand or area. Considerable branch dieback is caused by Melanconis juglandis (E. and E.) Graves, a fungus that appears to attack trees of low vigor. Anderson and LaMadeleine (1978) reported that Melanconis oblongum Berk is associated with dieback in branches and twigs, causing deformation but not tree mortality. Although butternut canker is the primary global threat to this species, butternut is also threatened to some extent by plant succession in areas where the pre-settlement disturbance regime no longer exists, preventing the creation of open conditions necessary for the successful reproduction of this shade-intolerant species.
Conservation needs include compiling a more accurate assessment of the problem, such as determining the degree of damage, how widespread the disease is, the distribution of the species and the disease, and also assessing forest health and trends. Research needs include studies of the disease and disease vectors, and the development of improved screening techniques for determining resistant strains of butternut for germplasm preservation and testing. Research is being directed toward the identification and propagation of disease-resistant trees. The North Central Forest Experiment Station of the U.S. Forest Service is coordinating research with several state agencies, universities, and private individuals in a three-part study to: (1) plant grafted clones of butternut in the field from resistant trees; (2) find methods of propagating these clones; and (3) develop the techniques for producing butternut tissue ("somaclones") that can be inoculated in order to determine which germplasm is disease resistant (Forest Service News 1992). One management technique is simply to avoid cutting healthy trees such that potentially resistant individuals can ultimately be identified. It will be important to identify and monitor significant butternut stands to help determine disease invasion and spread. When apparently resistant trees are found, these individuals can be utilized for germplasm testing, propagation, and preservation.
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