Influence of static bending stress on growth and wood characteristics of nine-year-old Douglas fir from two geographic sources Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/j9602407w

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  • The form of a tree stem and the properties of the wood comprising a stem may be determined by the strength requirements of that stem. If this is true, a tree will react physiologically to stresses which are imposed on a stem. This study was designed to investigate the influence of static bending stress on the growth and wood characteristics of Douglas -fir. Twenty-four nine –year-old Douglas-fir trees from two geographic sources were divided into three treatments. The treatments used were control, low bending stress, and high bending stress. Trees in the low and high treatments were bent with a horizontal force at a point 4. 5 ft. from the base, so that a low and high bending stress, respectively, would be produced in the trees. Bending caused another variable to be introduced into the experiment. That variable was a transverse component of gravity which influenced the low and high treatment trees. The influence of stress and gravity was studied on the diameter, radial, and leader growth of the trees and also on the specific gravity and tracheid length of the wood which was produced. Treatments did not cause a significant change in diameter growth. Radial growth was increased in treatment trees on the side of stems which was under compressive stress. The greatest increase in radial growth occurred in the lower parts of stems from 2. 5 ft. to the base. Leader growth was significantly decreased by the treatments with the greatest decrease in high stress trees. The treatment thus caused a redistribution of wood formation from the higher parts of stems to the lower parts of stems. Stress is thought to be the factor influencing this downward redistribution of wood and causing the increase in radial growth in the lower parts of stems. Specific gravity of wood formed was increased by treatments, but only on the side of sterns containing compressive stress. The greatest increase was at 4. 5 ft. and 2. 5 ft. , with only a small increase at the base. The increase in specific gravity was associated with compression wood formation. The increase in specific gravity and associated compression wood formation is believed caused by the transverse component of gravity rather than by any stress influence. Treatments also caused a decrease in tracheid length of wood formed on the sides of stems containing compressive stress. This decrease in tracheid length appeared to be associated with the increase in radial growth which occurred on treatment trees and also with compression wood formation. This study indicates that the function of compression wood is not to resist stresses in trees, but rather possibly to cause a bent or leaning tree to reorient itself in the vertical position. In order to resist stresses in stems, trees produce increased amounts of normal wood. In this way a greater cross sectional area of a stem is available to resist the imposed stresses.
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