Geographical distribution of an 18th-century heart rot outbreak in western juniper (Juniperus occidentalis spp.occidentalis Hook.)

Between 1749–1730 a widespread occurrence of fungus-caused heart rot affected western juniper in the interior Pacific Northwest, U.S.A. In this study 12 Juniperus occidentalis spp. occidentalis chronologies collected from various sites throughout the western juniper range were examined. The presence of heart rot precluded dating many of these samples prior to the 1730s. Subsequently, sample size decline in these chronologies was examined and it was found that a substantial decrease in chronology sample size was present in nine chronologies, with no other periods exhibiting a decline of equal magnitude. Since heart rot requires open wounds to establish, and the major heart rot episode was confined to a short period, we suspect that a regional–scale climatic event such as a windstorm or icestorm was the initiating cause of this outbreak.