Researchers from Britain's Center for Ecology and Hydrology at Wallingford said people who wore hiking shoes or rubber boots in an experiment transported seeds more than 3 miles, the study published in The Proceedings of the Royal Society B: Biological Sciences found.

In the experiment, people wearing those shoes stepped in mud, then in a tray containing a specific number of wild-plant seeds. They then walked a given distance, from 1 meter (3 feet 3 inches) to 5 kilometers (a little over 3 miles).

Seeds remaining on the shoes were then counted.

While most seeds fell off in the first 20 meters, or about 65 feet, some stayed on the shoes for the 3-plus miles, the study found.

By contrast, dispersal by wind is generally limited to about 250 meters, or about one-sixth of a mile, the study said.

Researcher Matthias Wichmann told The New York Times that while long-distance dispersal by walking is probably rare, it might have a profound effect on the spread of certain species, particularly invasive ones new to a region.

"Only a few seeds may go very far," he said. "But these are the pioneers -- they colonize new sites."