Status of black walnut (Juglans nigra L.) in the Eastern United States in light of the discovery of thousand cankers disease
Abstract
Juglans nigra (black walnut) is widely distributed throughout the US eastern forest, with high concentrations occurring in Missouri and the Ohio and Tennessee River basins. It is an extremely desirable tree for wildlife forage and timber production on forest land, and for shade, aesthetics, and wildlife forage in urban areas. Current (2009–2010) estimates from US Forest Service Forest Inventory and Analysis (FIA) data indicated that there were 306 million live black walnut trees in the eastern United States with a live volume totaling 112.76 million cubic meters (m³). This resource is currently threatened by the newly discovered presence of thousand cankers disease (TCD) in Pennsylvania, Tennessee, and Virginia. Thousand cankers disease may have been present in these areas for at least 10 years prior to discovery; however, no evidence of TCD in the forest at large was apparent in the crown condition and mortality data collected by FIA between 2000 and 2010. During this time period black walnut crown conditions were within the range of what is typically considered normal and healthy for hardwood trees and dead black walnut accounted for < 5% of the total number of black walnut trees in 82% of the counties where black walnut occurred. Lack of evidence of TCD in our study could be due to its actual absence or to an inability of the inventory and monitoring system to detect its presence.