Spruce Beetles Attack Slowly Growing Spruce

Abstract White spruce ( Picea glauca (Moench) Voss) stands were examined in 1982 to determine the relationship of tree growth to spruce beetle attack in an active spruce beetle ( Dendroctonus rufipennis (Kirby)) infestation on the Kenai Peninsula of Alaska. Conservative statistical comparisons showed that mean recent radial growth of unattacked trees on 25 plots sampled in 1982 was higher than radial growth of unsuccessfully attacked or beetle-killed trees. Mean radial growth of trees killed by beetles in 1982 did not differ significantly from radial growth of trees killed before 1982, but radial growth of trees unsuccessfully attacked in 1982 was significantly higher than radial growth of trees killed by beetles before 1982. In addition, trees killed in 1982 had significantly higher density of completed egg galleries than trees unsuccessfully attacked in 1982, but did not differ in diameter. Larger average tree diameters and faster radial growth rates of spruce occurred in stands with lower stocking levels. Results suggest that stand resistance to spruce beetle could be enhanced by decreasing stocking to reduce tree competition and increase vigor of residuals. Forest Sci. 31:839-850.