Butternut Genetic Resourcestternut Genebank
Butternut: Julans cinerea L.
Extracted and adapted from: Keith Woeste, Lenny Farlee, Michael Ostry, James McKenna, and Sally Weeks. 2009. A Forest Manager’s Guide to the Butternut. NORTHERN JOURNAL of APPLIED FORESTRY 26(1)9-14.
Butternut (Juglans cinerea L.), also called white walnut or oil nut, grows in the northeastern quarter of the United States. Although butternut is capable of achieving 110 ft in height with a diameter approaching 5 ft, mostly much smaller trees are alive today. Butternut wood qualities once made fine furniture, interior finishing, carving, musical instruments, and boats. Butternut is now threatened, and in many parts of its range, it is rare. The US Forest Service Forest Inventory and Analysis (FIA) data revealed that the number of butternuts across seven mid-western states decreased across all size classes by 23% from the previous survey. A survey of butternut in Wisconsin, in 1992, found 92 % of butternut trees were diseased, and 27% were dead.
Butternut Canker Disease
Butternut trees are being killed by Sirococcus clavigignenti juglandacearum, a fungus found throughout the native range. As of 2010, this disease is not present west of the Rocky Mountains. Although butternut is affected by other insect pests and diseases, canker is the most serious threat to the butternut species survival. Butternut canker was first reported from southwestern Wisconsin in 1967, but it was most likely introduced from outside North America, more than 40 years before.
Rain-splash is the primary means of spore dispersal, but long-distance movement by insects and birds is possible because isolated butternuts can be infected. Young, annual cankers are elongated, sunken areas commonly originating at leaf scars and buds, and often have an inky black center and whitish margin. Older, perennial branch and stem cankers are found in bark fissures or are covered by bark and bordered by successive callus layers. Cankers can develop throughout a tree, but commonly occur on the main stem, at the base of trees, and on exposed roots. As butternut canker disease progresses, cankers coalesce, eventually girdling and killing the host. Canker often kills butternuts quickly, but on occasion affected trees live as long as 30 years. Multiple branching or basal sprouts are often evident on severely affected trees, but these shoots typically succumb to the disease quickly. Black walnut and other species in the genus Juglans can also be infected by canker, resulting in branch and twig dieback in some cases. So far only butternut has been seriously impacted by the fungus.
Legal Status and Certification Issues
Butternut is not currently a federally protected species under the Endangered Species Act (ESA). It is listed by the federal government as a species of special concern, meaning it could be under consideration for ESA listing, but insufficient supporting information is available at this time. Canada listed butternut as an endangered species in November 2003. NatureServe, a nonprofit organization of natural heritage programs, provides a global conservation status listing of G4 for butternut, meaning the species is considered apparently secure from extinction. They note the species is in rapid decline, and its conservation status should be reevaluated frequently. Some states have highlighted butternut’s status by giving it a special designation beyond its status in NatureServe; Arkansas, Georgia, Kentucky, Massachusetts, Ohio, Tennessee, New York, Minnesota, West Virginia, and Wisconsin have officially listed butternut as a species of special concern, threatened, or vulnerable or placed it on a watch or special inventory list. Some federal and state agencies have established management policies aimed at retaining butternut on public lands. This includes Minnesota and nearly all the national forests within butternut’s range. The decline of butternut and its listing as a species of concern may have implications for management, particularly within the framework of forest certification. Principles and indicators for conformity with sustainable management practices in these systems include statements on retaining biological diversity and protecting rare, threatened, or endangered species. Although butternut is not officially listed in the United States, its declining population and the increased incidence of canker indicate the need for management to sustain local populations in situ. In addition ex situ collections should be established to preserve diversity of the species.
Ex Situ Collections in the United States
US Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository-Corvallis, 33447 Peoria Road, Corvallis, Oregon, 97333-2521: About 25 genotypes preserved for nuts and timber in a cultivated orchard.
US Department of Agriculture, Forest Service, Hardwood Tree Improvement and Regeneration Center, Northern Research Station, W. State Street, West Lafayette, Indiana 47907-2061: About 500 genotypes preserved in a forest plantation.