Vortex Rings from Sphagnum Moss Capsules

TL;DR

This study demonstrates how Sphagnum moss capsules produce vortex rings that effectively elevate spores for wind dispersal, overcoming limitations of non-vascular plant height and ballistic spore travel.

Contribution

It reveals a novel fluid dynamics mechanism where Sphagnum moss generates vortex rings to enhance spore dispersal height.

Findings

Vortex rings carry spores over 10 cm high

Spores reach initial velocities of 16 m/s

Ballistic spores would only travel 2-7 mm

Abstract

Long distance wind dispersal requires small spores with low terminal velocities, which can be held aloft by turbulent air currents until they are deposited in suitable habitats for colonization. The inherent difficulty in dispersing spores by wind is that spores easily carried by wind are also rapidly decelerated when moving through still air. Thus the height of spore release is critical in determining their range of dispersal. Vascular plants with wind dispersed spores use the height of the plant to lift spores into sufficient wind currents for dispersal, however non-vascular plants such as Sphagnum cannot grow sufficiently tall. These fluid dynamics videos show how exploding capsules of {\em Sphagnum} moss generate vortex rings to carry spores to heights above 10 cm with an initial velocity of 16 m s$^{-1}$. In contrast spores launched ballistically at these speeds through still air would travel only 2-7 mm.