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.
Damschen said the vast majority of seeds fell within 33 feet of the mounted boxes, and about 20 percent of them drifted 33 to 164 feet away. But one percent of the seeds, mostly in patches of land connected by corridors, traveled several hundred feet, she said, and the farthest was found more than a thousand feet away. The corridors in the forest, oriented in the direction of prevailing winds, acted like wind tunnels between tall buildings in a city, she said, speeding and in some cases redirecting the air flow to the end of the corridor.
Seeds released in the rectangular-shaped blocks of land with no connecting corridors moved the shortest distances, she said. Seeds from other types of plants may be spread by birds, mammals or ants, she said, or may explode out of pods that dry out and snap open.
Corridors are important, said University of Colorado ecology assistant professor Kendi Davies, because many plant and animal species are endangered and exist only in isolated habitats that are like islands on the landscape. Connecting those islands will help the species survive by increasing genetic and biological diversity.
“Understanding the details will help land managers make better informed decisions about the best ways to use corridors to conserve and restore landscapes,” said Davies, who was not part of the study.
Linked corridors of protected land are helping to protect endangered birds, fish and grizzly bears that move across the landscape, including one initiative that connects mountain terrain between Yellowstone National Park and Canada’s Yukon Territory.
Damschen, who was raised in Hopkins, said that compared with animals, much less is known about how plants move, even though conservation groups spend millions of dollars trying to preserve or restore tallgrass prairies and oak savannas in Minnesota and the Dakotas. Where land isn’t available, or large acreage isn’t feasible to purchase, she said, conservationists could work with farmers and other landowners to set aside smaller amounts of land to link the endangered ecosystems.
Connections would also benefit other types of plants since the wind also moves insects, spiders, pathogens, fungi and pollen.
“A lot of plants are also wind pollinated, and by moving their genes that way, that could also be another way that corridors would work,” she said.