Although roads cover a tiny part of the United States, they affect the ecology of much of the land nationwide, according to new research presented by Richard Forman of the Graduate School of Design at Harvard University in Cambridge, Massachusetts, in the February issue of Conservation Biology.
The four million miles of public roads and roadsides in the U.S. cover only 1% of the country, an area the size of South Carolina or Austria. But Forman estimates that roads directly affect the ecology of nearly 20% of U.S. land. Forman based his estimate on the conservative assumptions that the average "road-effect zone" extends several hundred feet on each side of roads in rural areas and half a mile in heavily-traveled developed areas. He got these distances from his own study in Massachusetts and studies by others in the Netherlands.
Roads can block the migration of animals such as moose and salamanders, and may spread non-native species. Roads can also affect aquatic ecosystems because streams are often channelized or rerouted, and wetlands are often partially drained. In addition, traffic noise can reduce the abundance of birds by a third; scientists believe that road noise makes it hard for birds to communicate while incubating their eggs and raising their young.
While the ecological effects of roads are mostly negative, it doesn't have to be this way. Awareness of the extent of roadside effects can help people meet both transportation and conservation goals, says Forman. For instance, people can restore roadsides with native plants, providing habitat for butterflies, birds and other animals. Many roads in agricultural areas of Australia are bordered by nature reserves. People can also find ways to help animals cross roads safely. Fourteen European countries are collaborating to build wildlife underpasses, overpasses and tunnels in an effort to reconnect habitat that has been fragmented by roads.