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Abstract Detail



Developmental and Structural Section

Goodrich, Katherine [1], Ortiz, Luis [1], Coughlin, David [1].

Twisty twigs: Biomechanics of storm resistance in distal branches of pawpaw (Asimina triloba).

Distal woody branches and associated foliage are at great risk of damage during storm events, largely as a result of high and fluctuating wind loads. Pawpaw (Asimina triloba), a temperate, hardwood species of the tropical family Annonaceae, has large oblanceolate leaves occurring on the distal portion of new growth along thin (3-7mm diam.) branches. Following a storm, branches of pawpaw exhibit a distinctive "flipped" orientation which slowly returns to an upright orientation over the next 24 hours. We examined torsional stiffness (GJ), flexural stiffness (EI) and viscoelastic creep in twigs from pawpaw and the co-occuring species tulip tree (Liriodendron tulipifera) and bitternut hickory (Carya cordiformis). These additional species do not exhibit the "flipping" phenomenon, yet have similar leaf areas and distal twig diameters. Pawpaw has lower torsional stiffness compared to tulip poplar and hickory, as indicated by the ratio of EI to GJ (or the "twistiness" to "bendiness" ratio). In addition, only pawpaw showed significant torsional creep followed by relaxation or return to initial orientation. We suggest that this biomechanical mechanism of woody distal twigs in pawpaw allows for reconfiguration of the large leaves in heavy wind/rain to reduce damage. Viscoelastic torsional creep of woody twigs differs from mechanisms involving long petioles or compound leaf morphology observed to reduce storm damage of foliage in other woody species.

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1 - Widener University, Department of Biological Sciences, Kirkbride Hall, 1 University Place, Chester, PA, 19013, USA

Keywords:
Biomechanics
storm resistance
viscoelastic creep
distal twig.

Presentation Type: Oral Paper:Papers for Sections
Session: 15
Location: Jasperwood/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 8:15 AM
Number: 15002
Abstract ID:398
Candidate for Awards:None


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