Meeting Abstract
Distal woody twigs and their associated foliage are at risk of mechanical damage during storm events, largely due to high and fluctuating wind loads. Distal twigs of pawpaw (Asimina triloba) exhibit an unusual phenomenon during/following storm events, whereby the twig “twists” so that distal leaves are held in an upside-down orientation. Twigs then re-orient to an upright position typically within 24 hours of the storm event. Immediately following a storm event, a “twisted” twig will hold its upside-down orientation even when manually flipped to its normal orientation. We hypothesize that this “twisting” twig behavior might minimize storm damage of distal woody twigs and associated foliage. We have measured flexural stiffness (EI), torsional stiffness (GJ), and viscoelastic creep in first year’s growth and second year’s growth for twigs of pawpaw and two co-occurring species which do not exhibit this “flipping” phenomenon. Pawpaw maintains low GJ values across a range of twig diameters relative to other species in our study, and only pawpaw demonstrates viscoelastic creep (and relaxation from creep). We present video of this flipping phenomenon in the field, and provide preliminary data on leaf/twig re-orientation for distal twigs in high winds. We are currently studying cross-sectional tissue composition for twigs of pawpaw and the other study species to identify potential composition/structural differences which may contribute to the different biomechanical properties recorded.
