Experimental Measurements of Terminal Velocity of Fern Spores

Abstract

The dispersal of diaspores is a key process for successful reproduction, survival and evolution of plants. To model the dispersal of biological propagules (e.g., spores, pollen) it is necessary to measure their terminal velocity (Vt) in air. In this study, we used a new method based on video image analysis to measure Vt of spores of seven fern taxa. The average Vt of fern spores was 7.0 cm s−1, but varied among species from 1.6 to 11.3 cm s−1. Similar values were reported previously for airborne particles of mosses and seed plants. Spores of Danaea nodosa and Lophosoria quadripinnata had a lower Vt than other spores of similar size, perhaps owing to their surface ornamentation that increases their drag coefficient, or an air cavity, which diminishes their density. The reliability of the video image analysis method used here on fern spores was verified by comparing observed and theoretically calculated Vt of glass beads of known diameter and density. This method also allows the observation of spore behavior (e.g., rotation) as they move through the air. Because the method is relatively easy and inexpensive, it can promote future aerobiological research on other biological airborne particles as well.