Torque is a vector component of wind acting on a growing tree. Mechanical devices which were attached to the tree were used to twist a single internode, which simulated the torque component in the absence of bending.Treatments either in a clockwise or counterclockwise direction were initiated at 20° and increased periodically through the entire growing season. Grain angle changed as much as 250% and radial growth was enhanced by as much as 100%, but fiber length decreased 20%.
Under natural conditions, the tree is stressed statically by the mass of the crown and bole. Pairs of steel rods drilled through two branch whorls were connected by turnbuckles to simulate increasing static load on a given internode. Level of soil moisture was included to discern its influence on the effect of static loading.Compression and moisture stress each reduced radial growth. After computed loading exceeded the proportional limit, the next-formed fibers were greatly expanded radially and, when macerated, exhibited extreme twisting. The fibers produced before the proportional limit was exceeded exhibited compression failures when macerated.
Two studies were made of the effects of stem vibration on tree growth and anatomical structure. Vibration was used to simulate wind sway.The results of a greenhouse and an outdoor study were not consistent but did suggest that vibration might cause a short-term reduction in growth. There was no evidence that the level of vibration used caused any change in wood structure.Soil moisture affected anchorage of the tree in the soil. This, in turn, affected lateral displacement resulting from vibration and influenced the redistribution of the new volume growth.
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