Leaves in the lowest and highest winds: temperature, force and shape

Authors


Author for correspondence:
Steven Vogel
Tel:+1 919 684-3791
Email: svogel@duke.edu

Abstract

Contents

  • Summary 13

  • I. Introduction 13
  • II. Very low but steady wind 14
  • III. Very low and fluctuating wind 17
  • IV. Very high winds 20
  • V. Leaf form as adaptation 23
  • Acknowledgements 24

  • References 24

Summary

Climatic extremes can be as significant as averages in setting the conditions for successful organismal function and in determining the distribution of different forms. For lightweight, flexible structures such as leaves, even extremes lasting a few seconds can matter. The present review considers two extreme situations that may pose existential risks. Broad leaves heat rapidly when ambient air flows drop below c. 0.5 m s−1. Devices implicated in minimizing heating include: reduction in size, lobing, and adjustments of orientation to improve convective cooling; low near-infrared absorptivity; and thickening for short-term heat storage. Different features become relevant when storm gusts threaten to tear leaves and uproot trees with leaf-level winds of 20 m s−1 or more. Both individual leaves and clusters may curl into low-drag, stable cones and cylinders, facilitated by particular blade shapes, petioles that twist readily, and sufficient low-speed instability to initiate reconfiguration. While such factors may have implications in many areas, remarkably little relevant experimental work has addressed them.

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