ÃÈÃÃÉçÇø

Two physicists from the Technical University of Denmark have found that leaf shape is a determining factor in the distance leaves travel as they fall from their tree. In their paper in the Journal of the Royal Society Interface, Matthew Dominic Biviano and Kaare Hartvig Jensen describe how they built a device that allowed them to mass-test falling leaves and what they learned through its use.

As tree leaves have evolved over millions of years, they have come to take on a wide variety of shapes and sizes. Trees use their leaves to conduct photosynthesis, to harvest water and for many other purposes, all of which likely contribute to their shape. In this new effort, the researchers wondered if shape might also serve another purpose: helping the tree keep its nutrients.

Prior research has shown that approximately 40% of the carbon sequestered by trees is carried out by leaves dying and falling to the ground where they decay and their carbon along with other nutrients make their way back into the soil. That carbon and those nutrients, the research pair noted, would only provide future benefits to the tree, if the leaves fell close enough for them to be reclaimed. That led the pair to wonder about the factors that lead to leaves falling straight down, or being carried aloft for some distance.

In watching leaves fall, it became clear to the researchers that the determining factor was leaf shape. To find out which leaf shapes led to leaves falling closest to their tree, the pair built an automated device that could shed 100 artificial leaves, made of paper, inside a water tank. The water, they note, allowed the leaves to fall slower than in the air, making it easier to watch and measure their descent.

In studying their data, the research pair found that the most important factors determining leaf drifting were symmetry and lobedness. The more symmetrical a leaf, the faster its descent, giving it less opportunity to drift. Fewer lobes also led to a faster descent. Asymmetry, they noted, resulted in spinning, which greatly slowed the descent, resulting in some leaves being carried too far for their carbon and nutrients to be reclaimed by their home tree.

© 2025 Science X Network