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Arboriculture & Urban Forestry Online
Volume 43, Issue 2 — March 2017

Does Modulus of Elasticity Vary Due to Dormancy and Temperature?    (View PDF)

Gregory Dahle, Aaron Carpenter, David DeVallance, and Mo Zhou

Abstract: The Intergovernmental Panel on Climate Change states with high confidence that extreme climactic events pose high risks on services such as electric service grids. Some of the extreme events will likely take place earlier in autumn, before deciduous trees complete the process of becoming dormant. The presence of leaves in a transitional season—before leaf drop (pre-dormant)—can be of concern if an unseasonal snow or ice storm occurs, as compared to after leaf drop (dormant). Researchers harvested stump sprouts and measured the flexural modulus of elasticity (E) of wood to determine if it varies with seasonality (pre-dormant versus dormant) and with temperature (frozen -6.7°C versus warm 21.1°C) using a universal load press. While dormant sprouts (warm and cold) had higher average flexural elasticity than the warm pre-dormant sprouts, they were not statistically different than the cold pre-dormant sprouts. As such, it does not appear that the modulus of elasticity differs as trees enter dormancy. Surely, the presence of leaves will increase the bending moment that may lead to an increase in failure, but the slight increase in elasticity as trees enter dormancy should not reduce the likelihood of watersprouts undergoing significant bending during a snow or ice storm.

Keywords: Biomechanics; Climate Change; Dormancy; Flexural Elasticity; Modulus of Elasticity; Northern Red Oak; Quercus rubra; Temperature; Utility Arboriculture.

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