BALSAM WOOLLY ADELGID (HOMOPTERA, ADELGIDAE) EFFECTS ON WOOD AND BARK STRUCTURE OF FRASER FIR AND SILVER FIR

Response of Fraser fir, Abies fraseri (Pursh) Poiret, to the balsam woolly adelgid, Adelges piceae (Ratzeburg), was evaluated by studying wood cores and bark samples taken from six sites near Mount Rogers, VA, and five sites in the Black Mountains of North Carolina surrounding Mount Mitchell. For comparison, samples were also collected from silver fir, Abies alba Miller, at four sites in the Black Forest of Germany. Average A. piceae densities were higher on trees at Mount Rogers than on Mount Mitchell trees. Proportions of trees producing abnormal wood in response to low or moderate A. piceae densities was greater for Mount Mitchell trees than for trees at Mount Rogers. Results from Mount Rogers support observations made for other fir species that A. piceae infestation induces outer bark formation, leading to tree recovery. Outer bark formation in trees from the Black Mountains and the Black Forest of Germany was not correlated with A. piceae density. There was indirect evidence that the outer bark measured in Mount Mitchell trees was incompletely formed, with an indistinct boundary layer between living and nonliving bark layers.