Children marvel at helicopter seeds spinning through the air from maple trees, or the wispy white seeds that riffle in the breeze and float like feathers from the split pods of milkweed plants. That same fascination has motivated researchers in a novel experiment to study how far seeds spread in the wind by using some workaday tools: yarn, fluorescent paint, black lights and computers.
The research, published in Proceedings of the National Academy of Sciences and directed by a University of Wisconsin scientist, could have relevance for threatened Minnesota ecosystems such as prairies, grasslands and savannas. It used tiny fake seeds made from bits of twisted yarn to mimic how far natural seeds of similar size and weight would drift in the wind.
"We just don't think very often about the fluid around us, which is air," said Ellen Damschen, University of Wisconsin-Madison assistant professor of zoology. "To visualize and understand what's happening in the air is very revealing."
Knowing how far seeds spread naturally could help conservationists connect patches of endangered prairie and grasslands that are otherwise isolated, Damschen said. It could also help determine whether plants can move across a landscape if local climate changes enough to jeopardize their survival in particular areas.
Damschen said that conservationists and others have long assumed that no one needs to worry about wind-dispersed seeds from plants like milkweed or prairie grasses because the breeze will blow them long distances and in all directions. That's not true, she said, any more than it's true that fish can go anywhere in marine systems. They both tend to move in currents that often connect specific locations, she said.
To test how far seeds can spread, Damschen and a team of researchers worked with help from the U.S. Forest Service on a longleaf pine plantation on federal land in South Carolina. Ten large areas of different shapes, each about the size of a city block and some of them connected by narrow corridors, have been cut into the forest. The patches have been used for a variety of large-scale outdoor research on plant diversity and other questions for more than a decade.
Damschen's experiment, funded by the National Science Foundation, released mock seeds in each block of land about a half-dozen times during 2008 and 2009. Researchers had prepared tiny yarn fragments by twisting them and dusting them with fluorescent paint. They placed the "seeds" in mounted boxes, and released them every 30 seconds for half an hour on windy days.
They then collected the mock seeds at night by using black lights that illuminated their fluorescent colors in the dark, recorded how far the seeds traveled, and compared the results with computer models.
