Scattering seeds is a prominent mechanism in all plants, often assisted by birds and gusts of wind. When birds eat the seeds of trees, they transport and defecate them, creating a randomized scatter where new trees will grow. When caught in a gust of wind, seeds fall and end up growing in close vicinity to one another. To increase the reach of where their seeds are planted, maple tree seeds twirl in a tornado-like vortex, creating more lift than their non-twirling counterparts. The leading edge of the seed lowers the air pressure over the top of the seed, sucking the wind of the seed upwards, giving it extra lift, or extra travel time. This leads to a prolonged arrival at the ground, and more efficient dispersal.
The lift mechanism is similar to those of insects and hovering hummingbirds who use their wings to develop a continuous air vortex, sustaining their flight. The spinning motion created by the maple seed structure sustains a lift vortex which prolongs the flight. It’s also important to note that dead (brown-colored) seeds scatter further because they have an altered center of gravity from alive (green-colored) seeds. This is because the center of gravity in the seed is closer to the center of lift, similar to a paper airplane that is able to fly further than its opponents.
A video further explaining the mechanism can be seen here: https://www.youtube.com/watch?v=r4urT74yq6cEdit Summary
Detailed performance studies (4, 6, 8) revealed that autorotating seeds are able to generate unexpectedly high lift forces despite their small size and slow velocity. Like autorotating seeds, insect wings generate very high lift despite operating at angles of attack well above those that will stall conventional aircraft wings and helicopter blades
Leading-Edge Vortices Elevate Lift of Autorotating Plant SeedsScienceJune 11, 2009
“The twirling seeds of maple trees spin like miniature helicopters as they fall to the ground. Because the seeds descend slowly as they swirl, they can be carried aloft by the wind and dispersed over great distances. Just how the seeds manage to fall so slowly, however, has mystified scientists…The research, led by David Lentink, an assistant professor at Wageningen, and Michael H. Dickinson, the Zarem Professor of Bioengineering at Caltech, revealed that, by swirling, maple seeds generate a tornado-like vortex that sits atop the front leading edge of the seeds as they spin slowly to the ground. This leading-edge vortex lowers the air pressure over the upper surface of the maple seed, effectively sucking the wing upward to oppose gravity, giving it a boost. The vortex doubles the lift generated by the seeds compared to nonswirling seeds.” (Caltech Media Relations 2009)
[Video showing vortices can be downloaded from http://mr.caltech.edu/assets/619-mapleseed.mp4.]