General ecology of Juglans nigra L. and potential effects of thousand cankers disease in the eastern United States

Background/Question/Methods

The walnut twig beetle (WTB) and associated thousand cankers disease (TCD) was discovered in the eastern United States in 2010. Previously known to exist only in eight western states, the arrival of this disease complex to the eastern U.S. poses a threat to the survival of Juglans nigra L., one of the most valuable hardwood tree species in the U.S. To date WTB finds in the eastern U.S. have been concentrated in and around urban areas in Tennessee, Virginia, and Pennsylvania; however, if the WTB becomes established in rural forests it has the potential to devastate the J. nigra population and alter the dynamics of the eastern deciduous forest. The objective of this study was to describe the general ecology of J. nigra and highlight potential effects of TCD on community characteristics and ecosystem processes. Ecoregion, forest type, physiographic location, aspect, slope, and other data collected by the U.S. Forest Service Forest Inventory and Analysis Program were summarized to describe the stand-level communities in which J. nigraare found in the eastern U.S. Analyses were limited to fully forested plots of natural origin with at least one live black walnut tree.

Results/Conclusions

Results support the typical growth pattern of J. nigra as scattered individuals or as small clusters in mixed hardwood stands. J. nigra was found on forested plots in 16 different ecoregion provinces across 30 states in the eastern U.S. Plots with J. nigra were classified into 53 unique forest types, with 79 percent of the J. nigra trees occurring in the oak/hickory forest type group. The majority of J. nigra occurred on mesic rolling uplands, sites with less than 20 percent slope, and sites with northwest to northeast aspects. Species from 55 different genera were found on the plots with J. nigra. Half of the co-occurring species were from the Quercus, Acer, Carya, and Ulmus genera. Depending upon how TCD spreads throughout the eastern U.S., a wide variety of forest conditions could be affected; however, the scattered nature of J. nigra may minimize the effect of TCD on the species population and general ecosystem overall.