Graduate Thesis Or Dissertation
 

The effects of balsam woolly aphid infestations on wood anatomy of true firs

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  • Three species of true firs in the Pacific Northwest--Abies gran-dis, grand fir; A. amabilis, Pacific silver fir; and A. lasiocarpa, subalpine fir--are severely damaged or killed by an imported insect pest, the balsam woolly aphid (Chermes (Adelges) piceae Ratz.), Infestations of this insect cause abnormalities in the wood and, in some cases, result in death of the tree. Wood samples were collected from five infested and five noninfested trees of each of the three species. Cross, radial, and tangential sections were taken from the wood samples, and samples were also macerated to separate the cells. Measurements were made of four anatomical characteristics: cell wall thickness, cell width, fibril angle, and tracheid length. Measurements were made of wood that was produced before infestation of the tree, wood of the same tree that was produced after infestation, and wood of noninfested trees. Wood produced after infestation in all three species is like compression wood in that the percentage of summerwood is greatly increased, tracheids are round in cross section, intercellular spaces are present, microscopic checking occurs in the cell waIIs, and false rings are present. The number of rays is almost double the number found in noninfested trees, and the diameter of the ray cells appears to be greater. Springwood cell walls of infested trees are sinuous in nature. Traumatic resin canals in tangential bands may be differentiated at any time during the growing season. Cell walls of the springwood of infested trees were significantly thicker than the springwood ceII walls of wood produced before infestation and also of noninfested trees for all three species, but there were no differences with regard to the summerwood. There were no significant differences in cell width for wood from each species. This was true for both springwood and summerwood. Fibril angle in the summerwood and transition area in infested trees of each species was two to three times greater than the angle found in wood produced before infestation and in noninfested trees. No differences in the fibril angle in springwood occurred. Tracheid length in infested wood was considerably reduced following infestation. Tracheids of wood produced before infestation, and in noninfested trees, were approximately one and one-half to two times longer than tracheids of infested trees.
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