Newswise — Plant invasions are rapidly becoming a threat to wildlands. One of the ways these aliens are dispersed is through large mammals that forage and excrete seeds in new locations. A new study has found horses to be a source of dispersal along recreational trails in Colorado. The study is published in the latest issue of Rangeland Ecology & Management.

Recreational trails in western wildlands represent corridors that connect the front country and the backcountry, and many trails are used by people with horses and other pack stock. The large number of horses on public lands and the potential for them to carry alien seeds could make horses an important vector for alien plant dispersal in remote wildlands.

In examining the ability of long-distance transport of plant species, the researchers sampled horse dung along the first 4,000 m of the Lower Piney River trail in the White River Forest of western Colorado. They found 20 species and 564 seedlings. The species were evenly divided between native and alien, but 85 percent of the seedlings were alien. Even though the alien species in the samples were common species that are not a priority for management, the study researchers said the important result was that horses have the potential to disperse a large number of seeds from a wide variety of plant types.

"With over 16,000 backcountry riders in the United States, a small decrease in the probability that the average horse will introduce a noxious plant into a public wildland could have a large influence on the ongoing invasion of native communities and ecosystems," said the study's researchers Floye H. Wells and William Lauenroth of Colorado State University.

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Rangeland Ecology & Management is published six times a year by the Society of Range Management. For more information, visit

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Rangeland Ecology & Management (Vol. 60(6), 2007)