Meeting Abstract

P1.93  Friday, Jan. 4  Twisty Twigs: Biomechanics of Storm Resistance in Distal Branches of Pawpaw ORTIZ, LA*; COUGHLIN, DJ; GOODRICH, KR; Widener Univ.; Widener Univ.; Widener Univ. kgoodrich@widener.edu

Woody plants can incur significant damage as a result of storm events. Following storms, pawpaw (Asimina triloba) exhibits distinctive reconfiguration of its distal twigs. Pawpaw, a temperate, hardwood species of the tropical family Annonaceae, has oblanceolate leaves (15-30cm in length) occurring on the distal portion of new growth along thin (3-7mm diam.) branches. Following a wind event, some terminal branches remain “flipped” or rotated 180 degrees. Within 24-48 hrs, these “flipped” branches return to a “right-side-up” conformation. We examined torsional stiffness (GJ), flexural stiffness (EI) and viscoelastic creep in twigs from pawpaw and two co-occuring tree species (tulip poplar and bitternut hickory). 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 of Vogel). In addition, only pawpaw showed significant torsional creep followed by relaxation or return to initial orientation. We suggest this is a biomechanical mechanism of pawpaw allowing reconfiguration of the leaves in heavy wind/rain in order to reduce damage.