In an attempt to gain a view of the big picture, the February 2000 issue of Conservation Biology dedicated a special section to the ecological effects of roads. This issue of Science Briefs highlights some of the findings from that section. Dr. Christopher Frissell, an aquatic biologist at the University of Montana, says the most important effects go beyond the mere construction of the road. Studies show that roadkill is threatening populations of frogs and toads that need to cross roads to complete their life cycles. Frissell notes that while roads are usually built for specific human activities, including transportation, recreation, or logging, the ecological effects usually go far beyond the intended use.
Roads can open an area to increased hunting, both legal and illegal, and invasion by exotic plants.
In the first attempt to quantify the total effect of roads on the American landscape, Dr. Richard Forman, a landscape ecologist at the Harvard Design School, estimates that roads affect almost one-fifth of the land area in the United States. That number is slightly higher if you exclude Alaska, which has a low road density. For this study, Forman identified the road impact reaching the farthest from the road at each point along the highway. The impacts included traffic noise affecting grassland birds, interruption of moose migration corridors, stream channelization, and wetland drainage. In some cases the road-effect zone reached only a few feet from the road, while in others it extended over half a mile into surrounding areas.