Roads Open Up Paths for Weed Invasions
From Environment News Service, Apr 18, 2003

DAVIS, California, April 18, 2003 (ENS) - Two new studies find that roads have a considerable impact on the spread of invasive species. The studies, conducted by researchers at the University of California at Davis (UC Davis), find that improved roads in wilderness areas spread more invasive weeds than primitive roads and that roadless areas act as refuges for native species against invasions.

Invasive weeds such as cheatgrass and knapweeds have settled on some 125 million acres of the American West - the studies document that roads promote invasion because vehicles can transport non-native seeds into uninfested areas, and disturbed roadsides give weed seeds a place to grow.

"These papers are timely in light of the debate concerning protection for roadless habitats in U.S. national forests," said Jonathan Gelbard, a UC Davis doctoral candidate and coauthor of both studies. "Our findings show that roadless habitats have multiple benefits, not just for the environment, but also for the economy and our quality of life."

"They are not only refuges for native biodiversity," Gelbard explained, "but also protect against non native weed invasions, which are costly for ranchers and public agencies."

One of the UC Davis studies, published in the April issue of "Conservation Biology," is an examination of 42 roads in and around Utah's Canyonlands National Park. Gelbard and research ecologist Jayne Belnap of the U.S. Geological Survey found that each step of road improvement converted an increasing area of natural habitat to roadside habitat, from which non-native weeds spread into adjacent natural ecosystems.

The second study, published by Gelbard and UC Davis professor of environmental science and policy Susan Harrison in the April issue of the journal Ecological Applications, explores the effects of roads on inland California foothill grasslands.

It found that that in areas with typical grassland soils, non-native plants were less abundant and native plants more abundant at sites about a half-mile from roads compared to sites less than 33 feet from roads.