Foliage motion under wind, from leaf flutter to branch buffeting

Abstract

The wind-induced motion of the foliage in a tree is an important phenomenon both for biological issues (photosynthesis, pathogens development or herbivory) and for more subtle effects such as on wi-fi transmission or animal communication. Such foliage motion results from a combination of the motion of the branches that support the leaves, and of the motion of the leaves relative to the branches. Individual leaf dynamics relative to the branch, and branch dynamics have usually been studied separately. Here, in an experimental study on a whole tree in a large-scale wind tunnel, we present the first empirical evidence that foliage motion is actually dominated by individual leaf flutter at low wind velocities, and by branch turbulence buffeting responses at higher velocities. The transition between the two regimes is related to a weak dependence of leaf flutter on wind velocity, while branch turbulent buffeting is strongly dependent on it. Quantitative comparisons with existing engineering-based models of leaf and branch motion confirm the prevalence of these two mechanisms. Simultaneous measurements of the wind-induced drag on the tree and of the light interception by the foliage show the role of an additional mechanism, reconfiguration, whereby leaves bend and overlap, limiting individual leaf flutter. We then discuss the consequences of these findings on the role of wind-mediated phenomena.

Nondestructive and Fast Vibration Phenotyping of Plants

“…In MFA, a more advanced processing is used, based on Bi-Orthogonal Decomposition (BOD). This general method of field decomposition has already been applied to analyze the motion of plants obtained by video capture in several cases such as crops canopies [ 9 ], trees [ 10 ], Arabidopsis thaliana [ 11 ], and foliage [ 14 ]. In these papers, the video capture was first treated by a Digital Image Correlation technique to derive the velocity field of the plant and its evolution in time.…”

“…Moreover, many of the Digital Image Correlation Techniques (DIC) that have been developed with success for vibration problems (see, for instance, [12,13]) are not well adapted to the present case of HTP on plants: they aim at both frequencies and modal shapes (a rich information, not needed here) and require high quality optical environment. The use of DIC to analyze the wind induced-motion of a full foliage [14] required lengthy image processing. Adapting plant vibration measurement to HTP is a challenge as the technique needs to be both nondestructive and fast (say about one minute per plant).…”

Mechanics of a plant in fluid flow

“…An obvious fertile ground for new research avenues in plant FSI is at the intersection between different phenomena. For example, Tadrist et al (2018) determined the transition between leaf flutter and turbulence buffeting of branches. Other potential questions one might ask is how does static reconfiguration affect stability and how in return do vibrations affect the loads perceived by the plant?…”

Wind speed inference from environmental flow-structure interactions, part 2: leveraging unsteady kinematics

“…These transfer functions depend on the tree-specific properties affecting the dynamics, including the natural frequency, damping, and drag coefficient. Prior work measuring tree sway also suggests that the magnitude of the tree sway increases with increasing wind speed (Peltola et al, 1993;van Emmerik et al, 2017), as does the velocity of the tree branches (Tadrist et al, 2018).…”