Forum: Balsam Woolly Adelgid (Homoptera: Adelgidae) and Spruce-Fir Decline in the Southern Appalachians: Assessing Pest Relevance in a Damaged Ecosystem

Robert G. Hollingsworth, Fred P. Hain

Abstract


Research on tree decline has shown that the proportion of sapwood area to heartwood area is an important measure of tree health. Infestation by the balsam woolly adelgid (BWA), Adelges piceae (Ratz.), causes the formation of abnormal wood, which is thought to conduct sap poorly. BWA infestation is also associated with lower (more negative) xylem pressure potentials and increased areas of heartwood. We hypothesize that lower pressure potentials (a consequence of abnormal wood production) increase the rate of cavitation (gas-filling) of sapwood tracheids, thereby accelerating heartwood formation. If this hypothesis is correct, adelgid attack causes loss of functional sapwood both directly and indirectly. There is evidence that the balsam woolly adelgid is an important factor causing the decline of Fraser fir, Abies fraseri (Pursh) Poiret, in the southern Appalachians. However adelgid damage is probably interacting with many other environmental factors to cause reductions in per cent sapwood area. Determining the relevance of this pest to tree decline can be accomplished by examing the relationship that exists between adelgid infestation, increment growth, and per cent sapwood area.

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