When Wildlife Hits the Road
The emerging science of road ecology is revealing new data about the effects of thoroughfares on wildlife populations
When landscape ecologist Richard Forman drives from his office at Harvard’s Design School in Cambridge, Massachusetts, to his home in the suburbs, there is really just one way to go—Route 2, a four-lane highway that traverses the northern tier of the state. Unlike most commuters in the 50,000 vehicles that travel this stretch each day, Forman does not see Route 2 as simply a means to an end. To him, it is a laboratory for studying the environmental effects of roads—part of an emerging field called road ecology that he helped found in the 1990s.
Forman’s investigations began a decade ago when he joined a National Research Council committee mainly focusing on transportation and greenhouse gases. It occurred to him that transportation impacts on biodiversity and water quality, among other environmental concerns, warranted equal consideration. "The road network is arguably the most conspicuous component of the landscape," he says, "and at the time we knew almost nothing about it ecologically." Forman has since devoted himself to uncovering the hidden consequences of America’s 4 million miles of public roads and quarter-billion vehicles, an effort that culminated last year in Road Ecology—the first comprehensive book on the subject, which he wrote with 13 other ecologists, hydrologists and transportation specialists.
Driving one afternoon along his research area, a 15-mile stretch of Route 2 in the outer suburbs bounded by Interstate Highways 95 and 495, Forman passes a power-line corridor where moose have wandered, spots where road kills most often occur, places where road salt and other contaminants infiltrate water supplies, former wetlands long ago drained and filled and the site of a 2002 oil spill that dumped 1,700 gallons into a water supply for the city of Cambridge, prompting a year-long cleanup.
Many of the highway’s effects are more subtle. Road shoulders, Forman points out, are made by mixing rock and soil and smoothing the surface. "We’ve taken the richness out of the land and monotonized it," he says. Ditches that channel water through culverts beneath roads "take the soft curves of nature and straighten them out," he says, "but those curves are habitats for fish and other important aquatic species."
Although road kill attracts the most public concern, Forman says, the loss of individual animals to traffic is generally unimportant to populations as a whole, except in the case of large predators. Harsh as it sounds, most of the victims belong to common species such as sparrows, rabbits and squirrels, which, he says, "reproduce faster than we can kill them." Fragmentation of wildlife habitat is more devastating. Route 2 poses a formidable barrier that partitions a once-unified landscape—in some stretches doing so with concrete walls. "Animals need room to move, to forage for food, to get water, to disperse and to mate," he says. When we block movement and isolate a population, the species faces a greater risk of local extinction.
To reconnect the land, environmental groups have proposed several wildlife underpasses and overpasses for Route 2. Forman supports the idea, which can work well, especially when structures are placed where wildlife corridors can connect large protected areas.
Noticing that deer and other animals often are repelled by highways with traffic, Forman wondered how far out from the roadbed ecological influences extend. Looking at factors such as animal road-avoidance behavior, impacts on aquatic systems and the spread of invasive species, he and his colleagues calculated a road-effect zone averaging roughly three-eighths of a mile wide around Route 2. He concluded that 20 percent of the nation’s land is directly affected by public roads, including the 1 percent already made into roads and roadsides. The impacts spread as more roads are built and more drivers venture off road.
Noise is particularly pervasive. Forman’s research team discovered that songbirds such as bobolinks and meadowlarks do not nest in fields located within three-quarters of a mile of Route 2. Bird presence was reduced along other busy roads, though small streets accommodating less than about 5,500 vehicles per day had no discernible influence on bird populations.
"People speeding by are oblivious," Forman says of the ecological effects brought by roads and vehicles. But if you spend time on the roadside, as he often does, you will find it a miserable place—noisy, dusty and dangerous. An obvious solution is to limit the amount of land used by vehicles. Paved road surfaces can be made quieter. Closing access roads in rural and remote areas provides sustained wildlife benefits. When expansion is needed, widening existing highways is far preferable to constructing new ones, Forman says. "If roads and traffic keep spreading," he adds, "there’ll be no place left for natural populations of animals."
Steve Nadis is based in Massachusetts.
Many Roads To Cross
The United States has 4 million miles of public roads, the largest road system in the world. Urban roads constitute a fifth of the U.S. network. The rest are rural, and nearly half of them are unpaved. The Interstate Highway System accounts for about 1 percent of U.S. public roads. The roads of the National Forest System account for about 10 percent.