Paving the Way for Weeds

08-01-2003 // Laura Tangley

BUILDING ROADS in a protected ecosystem is usually considered a bad idea, in part because they encourage invasion by exotic weeds. Vehicles carry nonnative seeds on their tires and in mud on their undercarriages, while clearings for road building and maintenance help exotics get established. Now a new study finds that not all roads are created equal.

In and around Utah's Canyonlands National Park, researchers surveyed plant life along 42 roads. Their results, published in Conservation Biology, show that with each step of road improvement--from four-wheel-drive track to graded, gravel and, finally, paved road--more exotic plants grew in the strips, or verges, along the sides of the road. Nonnative cheatgrass, for instance, was three times more abundant in verges beside paved roads than in those bordering four-wheel-drive tracks. Verges along improved roads were also wider--about three feet on each side of a four-wheel-drive track versus 23 feet on a paved road.

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