Natural frequency (f) and damping ratio (ζ) are important dynamic parameters that affect the likelihood of tree failure. Much work has investigated these parameters on conifers, but few data exist for open-grown deciduous trees. Considering the risk to people and property from tree failures in residential areas, a better understanding of f and ζ for open-grown deciduous trees is warranted. We measured free vibrations of Bradford pear (Pyrus calleryana Decne. ‘Bradford’) and chestnut oak (Quercus prinus L.) to calculate f and ζ. Subsequently, we remeasured trees after pruning and leaf-drop to investigate the effect of each treatment on f and ζ. While testing one species, an ice storm provided a serendipitous opportunity to investigate the effect of ice accretion on f and ζ. For both species, f did not differ with respect to the cycle for which it was measured or the direction in which the tree swayed. Different types of pruning variably affected f and ζ, but the effect of leaves superseded the effect of pruning, as well as ice accretion. Pruning trees to reduce the likelihood of wind-induced failure may thus be of limited value if significant wind events typically occur when trees are leafless.
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