Earth and Space News: Flexural Elasticity Modulus: Trees and Watersprouts Bend or Break

Summary: Flexural elasticity modulus leaves trees and watersprouts broken if inflexible and bending if flexible in dormant and pre-dormant loads and wind throws.

Elasticity is not low enough and flexibility is not high enough for this branch to bend, not break, during loading events and wind throws; red oak (Quercus rubra) with newly lost branch in Skaneateles Conservation Area, Onondaga County, west central New York: R.A. Nonenmacher, CC BY SA 4.0, via Wikimedia Commons

An article by four West Virginia University researchers in Morgantown for the March 2017 issue of Arboriculture and Urban Forestry asks, "Does the modulus of elasticity vary due to dormancy and temperature?"

The School of Natural Resources co-researchers broach bending forces from dynamic loading, mechanical loading, static loading of ice and snow and wind throw upon dormant trees. Gregory Dahle considers with Aaron Carpenter, David DeVallance and Mo Zhou overall loading events larger for ice- and snow-storms before dormancy of deciduous trees than during. The quartet describes the dormant stages in the Northern Hemisphere's temperate zones as drawing deciduous trees into leaf senescence (old age) during the autumn's changing weather.

Lower material properties in juvenile wood encourage watersprouts from electrical utility rights-of-way line-clearances or topping to bend, break, contact energized power lines and create power outages.

Flexural elasticity modulus furnishes "resistance of a material to elastic deformation when a bending type force is applied, within the linear portion of the stress-strain diagram." The dried, stiff wood in construction materials gets higher flexural elasticity modulus and greets higher loading events while green wood gets higher flexibility from lower elasticity.

Arborists have the relationship of flexural elasticity modulus, moisture and temperature for wood below fiber saturation point but not pre-dormant standing trees heading into changed temperatures. Moisture content increases after leaf drop in diffuse hardwood species whose material properties in construction-grade lumber and commercially important trees rainfall and temperature impel or imperil.

The study juggles dormant and pre-dormant seasonalities and frozen and warm temperatures to judge the flexural elasticity modulus of juvenile wood and the incidence of watersprouts.

The study keynotes 60 dormant and 60 pre-dormant heading cut-, storm damage-like naturally regenerated northern red oak (Quercus rubra) stump sprouts in Monongalia County Research Forest. It lists the first eight days in Feb. 2013 and all Sept. 2014 as dormant and pre-dormant sampling times for branches aged by proximal-end growth rings. It mentions pre-dormant warm samples' greater flexibility over 60 cold (minus 6.7 degrees Celsius, 19.94 degrees Fahrenheit) and warm (21.1 degrees Celsius, 69.98 degrees Fahrenheit) dormant. It notes insignificant flexural elasticity modulus differences between dormant sprouts and pre-dormant cold sprouts and no impact of leaves on pre-dormant sprout stiffness in cold weather.

Diameter, not age, moisture content, season, specific gravity or temperature, offers the only significant predictions of flexural elasticity modulus in the study's multiple linear regression model.

Increased diameter, possibly from weather-influenced wood formation between dormant and pre-dormant samplings, proves negative for flexural elasticity modulus since large-sized branches reveal greater flexibility than small-sized.

Fifty-plus percent moisture content in dormancy and pre-dormancy neither quells nor quickens flexural elasticity modulus in multiple and simple linear regression models or wood's material properties. A higher average specific gravity ranging around that of mature wood's average 0.65 rates as a possible explanation for increased average elasticity in dormant juvenile wood.

The flexural elasticity modulus stays steady for watersprouts that should not stray into energized powerlines and that should sustain unchanging flexibility during colder dormancies or pre-dormancies. Globally warmed climate change therefore teases arborists, gardeners, naturalists and stewards with scenarios, unlikely in the study, of trees and their watersprouts thwacking electric service grids.

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

shortleaf pine (Pinea echinata) with water sprouts at root collar in Ouachita National Forest, LeFlore County, southeastern Oklahoma: Robert F. Wittwer/Oklahoma State University/Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=4800031

For further information:

Dahle, Gregory; Carpenter, Aaron; DeVallance, David; and Zhou, Mo. 2017. "Does Modulus of Elasticity Vary due to Dormancy and Temperature?" Arboriculture & Urban Forestry 43(2): 49-54.

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

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Earth and Space News

Sunday, March 12, 2017

Flexural Elasticity Modulus: Trees and Watersprouts Bend or Break

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