"Each step of road improvement would appear to convert an increasing area of natural habitat to roadside habitat," say Jonathan Gelbard, who did this work while at Duke University in Durham, North Carolina, and is now at the University of California at Davis, and Jayne Belnap of the U.S. Geological Survey in Moab, Utah, in the April issue of Conservation Biology.
Cheatgrass, knapweeds and other non-native plants have invaded nearly 125 million acres of the American West. Roads are a big part of the problem: for instance, vehicles can transport non-native seeds into uninfested areas, and clearing land during road construction gives weed seeds a place to become established. Intuitively, it makes sense that improved roads would spread weeds more than primitive roads because the former have more traffic, more exposed soil and more maintenance such as mowing and herbicide treatments, all of which can favor invasive species.
To see if non-native weeds really are more likely to invade along improved roads, Gelbard and Belnap surveyed the plants along 42 roads with varying degrees of improvement (paved, improved surface such as gravel, graded and 4-wheel-drive track) in and around southern Utah's Canyonlands National Park. The researchers determined the cover and number of species of non-native and native plants in two areas: roadside verges (strips along the road), and "interior sites" near but not right next to roads (165 feet from the verge).
Gelbard and Belnap found that road improvement greatly increased the cover of non-native plants in roadside verges. Notably, cheatgrass cover was three times greater in verges along paved ro
Contact: Jonathan Gelbard
Society for Conservation Biology