Assessment of abiotic and biotic factors associated with eastern white pine (Pinus strobus L.) dieback in the Southern Appalachian Mountains

A novel and emerging eastern white pine (Pinus strobus L.) dieback phenomenon is occurring in the Southern Appalachian Mountains in the eastern United States. Symptomatic eastern white pine trees exhibit canopy thinning, branch dieback, and cankers on the branches and bole. These symptoms are often associated with the presence of a scale insect, Matsucoccus macrocicatrices Richards (Hemiptera: Matsucoccidae), and a fungal pathogen, Caliciopsis pinea Peck (Coryneliales: Coryneliaceae). We determined the extent, range, and severity of dieback of 2,061 eastern white pine trees from 40 sites in Georgia, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia. We also evaluated associations between eastern white pine health and abiotic (aspect, elevation, latitude, precipitation, slope, and temperature) and biotic (eastern white pine basal area and density, relative stand density, and presence of C. pinea and M. macrocicatrices) factors. Our results indicate that trees ≥2.54 cm DBH had an average health rating of 3.57 (1 = healthy tree, 5 = dead tree), with 57% being in the 4-5 health rating groups. Eastern white pine dieback was positively associated with presence of C. pinea, and negatively associated with mean annual temperature and tree size. Sawtimber (≥22.86 cm) were healthier than poletimber (12.70-22.61 cm) and sapling sized trees (2.54-12.45 cm). Further, C. pinea incidence was positively correlated with eastern white pine density and M. macrocicatrices. The insect-pathogen complex was present in all six states and 80% of the sites. If eastern white pine dieback continues, effective management practices will be needed to conserve and maintain this economically and ecologically important pine species in the eastern United States.