Juglans cinerea L.
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Basis for Listing
Until recently, Juglans cinerea (butternut) was a fairly common forest tree in the eastern half of the United States and Canada. Unfortunately, J. cinerea is very susceptible to butternut canker (Sirococcus clavigignenti-juglandacearum), a lethal fungal disease of unknown origin. The disease was first reported in Wisconsin in 1967 (Renlund 1971) and reached southeastern Minnesota in the 1970s. It has since spread throughout the state and throughout the North American range of J. cinerea. The fungus attacks the cambium, leaving a blackened elliptical area of dead cambium just beneath the bark (Ostry et al. 1996). When the number of cankers becomes too great, the branch or trunk is essentially girdled and dies. There is no known treatment or control for butternut canker, and few if any trees are immune. This tragic situation has progressed to the point where nearly all J. cinerea in Minnesota are now dead or dying. The species was listed as special concern in 1996. A status of endangered was considered at that time, but it was hoped the disease could be abated. Since that time, it has become clear the threat has not and will not likely be abated in the foreseeable future. For that reason, its status was elevated to endangered in 2013.
Juglans cinerea is a midsize to large tree, with moderately thick gray to gray-brown bark. The leaves are alternate on the stem and pinnately compound, with 11-17 individual leaflets. The male flowers are borne on a slender catkin, and the female flowers are on a short spike. The fruit is an ellipsoidal nut enclosed in a thin husk covered with sticky glandular hairs.
Juglans cinerea occurs in northern and central mesic hardwood forests in the Laurentian Mixed Forest Province and southern mesic hardwood forests in the Eastern Broadleaf Forest Province. The species occurs in loamy or alluvial soils or in sandy soil if the water table is relatively near the surface. It is perhaps most common on river terraces elevated several feet or more above the active floodplain, where it is protected from siltation and flood scouring (Smith 2008).
Biology / Life History
Until recently, J. cinerea was a fairly common tree in southern Minnesota, though it never occurred as a dominant tree. It was usually seen as scattered individuals or in small groves, typically with Quercus spp. (oaks), Prunus serotina (black cherry), Tilia americana (basswood), Acer saccharum (sugar maple), or Ulmus americana (American elm). Juglans cinerea is intolerant of shade, so it rarely reproduces in mature forests, unless there is a substantial gap in the canopy to provide light for seedlings. The greatest recorded age of a J. cinerea in Minnesota is 221 years (Hale 1996), which is probably near its maximum potential.
Conservation / Management
The main issue facing the conservation of J. cinerea is not loss of habitat but the spread of the lethal fungal disease known as butternut canker. In some areas, healthy and presumably resistant trees have been found growing adjacent to diseased trees. These trees, if they are truly resistant, could be extremely valuable in efforts to preserve the species, and they must not be cut down. Cuttings and seeds taken from disease resistant trees and propagated in tree plantations could potentially provide stock for landscaping purposes and possibly for reestablishing wild populations. It is also advisable to consider augmenting existing populations by direct planting of seeds taken from healthy trees.
Best Time to Search
When searching for J. cinerea, it is useful to know that the bark is distinctive and, with a little practice, can be recognized at any time of the year. The flowers appear in mid-spring, and the fruits develop throughout the summer, though neither flowers nor fruits are needed for identification.
Conservation Efforts in Minnesota
Since 1992, there has been a moratorium on the harvest of healthy J. cinerea trees from state lands administered by the DNR Division of Forestry. While the moratorium does not prohibit the salvage or harvest of infected or dying trees; in some cases, it may be appropriate to leave such trees for research purposes.
Welby Smith (MNDNR), 2008 and 2018
Elias, T. S. 1972. The genera of Juglandaceae in the southeastern United States. Journal of the Arnold Arboretum 53:26-51.
Hale, C. M. 1996. Comparison of structural and compositional characteristics and coarse woody debris dynamics in old growth versus mature hardwood forests of Minnesota. M.S. Thesis, University of Minnesota, St. Paul, Minnesota.
Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.
Ostry, M. E., and K. Woeste. 2004. Spread of butternut canker in North America, host range, evidence of resistance within butternut populations and conservation genetics. Pages 114-120 in C. H. Michler, P. M. Pijut, J. W. Van Sambeek, M. V. Coggeshall, J. Seifert, K. Woeste, R. Overton, and F. Ponder, Jr., editors. Proceedings of the 6th Walnut Council Research Symposium. General Technical Report NC-243. Department of Agriculture, Forest Service, North Central Research Station, St. Paul, Minnesota.
Ostry, M. E., and M. Moore. 2008. Response of butternut selections to inoculation with Sirococcus clavigignenti-juglandacearum. Plant Disease 92:1336-1338.
Ostry, M.E., M. E. Mielke, and R. L. Anderson. 1996. How to identify butternut canker and manage butternut trees. USDA Forest Service, North Central Forest Experiment Station Publication HT-70, St. Paul, Minnesota. 8 pp.
Renlund, D. W. 1971. Forest pest conditions in Wisconsin. Wisconsin Department of Natural Resources Annual Report. 53 pp.
Schultz, J. 2003. Conservation assessment for Butternut or White walnut (Juglans cinerea) L. United States Forest Service, Eastern Region, Milwaukee, Wisconsin.
Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.
Whittemore, A. T., and D. E. Stone. 1997. Juglans. Pages 425-428 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 3. Oxford University Press, New York, New York.
Woeste, K., and P. M. Pijut. 2009. The peril and potential of Butternut. Arnoldia 66(4):2-12.
Woeste, K., F. Lenny, M. Ostry, J. McKenna, and S. Weeks. 2009. A forest manager's guide to butternut. Northern Journal of Applied Forestry 26(1):9-14.