Species and Sprawl: A Road Runs Through It

Homo sapiens is particularly noted for its survival instinct, even when faced with some of the most perilous habitats on Earth. Consider Craig Mayhew, a long-time car commuter on the treacherous and tangled tarmac of the Baltimore-Washington metropolitan area. In 1997, Mayhew’s 56 km one-way commute along a toll road and the eight-lane beltway from Reston, Va., to Greenbelt, Md., usually took him 45 minutes. But as the 75-minute “bad days” grew more frequent, he began to telecommute two days a week, and then three.

In the last five years, Mayhew has had more opportunities than ever to employ his cunning, outwit the competition, and abandon the pack on his two weekly travel days. Around 1999, a new tech hub near Dulles Airport, including new headquarters for America Online and MCI, seemed to mushroom overnight. Development in a new suburb called Ashburn exploded to house the added workers. Loudon County, Va., saw its population hurtle from 57,000 in 1980 to nearly 222,000 in 2003, making it the fastest-growing county in the nation. “My commute grew to nearly two hours,” says Mayhew. He began hunting for alternatives to the highway, ferreting out labyrinths of local roads to avoid highway clogs. “I have become a master at interpreting traffic reports,” he says.

A move to a subdivision in Herndon, Va., 8 km further from work, required wilier tactics. One day, Mayhew abandoned his car for a 20-minute bus ride to a 1½-hour subway ride to a 45-minute local bus ride to a 10-minute walk to his office’s main gate. “Two hours, 45 minutes!” he fumes. “Impossible.” Two trials on his bicycle clocked in at two hours one-way.

“I can guarantee I’ll be out of my job by spring and out of the region by the end of 2005,” says Mayhew. “But does that mean I will contribute to and suffer from sprawl in another region?”

Given the current statistics on sprawl in the United States, it’s not unlikely.

For example, Mayhew could move to Phoenix, which is developing open land at a rate of 1.2 acres an hour. Or he could follow the masses to Atlanta, which, free from natural barriers to meandering development such as mountains or a limited water supply, expects to see its population double in the next 50 years. Odds are, Mayhew wouldn’t head to Cleveland—it’s been declining in population since 1970—but if he did, he could buy plenty of square footage; developed land in the city grew 33 percent during the same period.

Humans are shaping, and shaped by, sprawl—the rapid, poorly planned, low-density growth of homes and businesses far from urban centers. Sprawl is affecting Homo sapiens, just as it does many other species on this planet. It permanently alters our habitat, hampers our mobility, and diminishes our odds for survival. Here’s how:

An Altered Landscape

The desire for a safe habitat with ample food, shelter, protection from predators, and means of escape is instinctual for all living things. For many Americans, this instinct manifests itself as a single-family dwelling outside the city, with a patch of grass, a car in the driveway, and a mega-supermarket a few miles down the road. Yet each U.S. citizen today uses four to five times more land than he or she did in 1940. Construction of homes, pavement, and businesses is incurring a staggering, permanent loss of natural open land—more than 2 million acres of forest, prairie, desert, wetlands, and farmland are developed every year. Ecologically, economically, and aesthetically valuable wild lands such as the Midwest’s virtually vanished tallgrass prairie and Arizona’s diverse, fragile Sonoran Desert are at risk of disappearing or degrading completely.

Take the once pristine Chesapeake Bay, its shores not 80 km from Mayhew’s townhouse. Despite recovery efforts, the estuary remains severely polluted from its rapidly suburbanizing watershed. Sewage-treatment wastewater and fertilizer runoff prompt algal blooms that suffocate fish and blue crabs. Eroded sediment smothers oysters and blocks sun from vegetation. Chemicals from pavement runoff and vehicle and power plant emissions are proving toxic to the bay’s 3,000 species of plants and animals.

Developing on or near wetlands like the Chesapeake Bay is also changing the hydrologic cycle. When soil is topped by pavement or buildings, precipitation can no longer accumulate in wetland reservoirs or percolate gradually to underground aquifers. Instead, it runs off impervious surfaces haphazardly, bringing floods and pollution to both wild and metropolitan areas.

Decreased Mobility

Today, 6.4 million km of public roads link our homes, businesses, and parking lots. In fact, sprawl could not exist without vehicles. In historic communities, businesses, stores, and services were within a walkable distance from residences. But Mayhew, for example, must walk 1.2 km—and back—to get a quart of milk. In 1960, 12.1 percent of Americans took public transportation to work, and 9.9 percent walked. Today, 4.7 percent use public transport, and 2.9 percent walk.

Ironically, the proliferation of roads, compounded with ineffective zoning and rapid, as-needed planning, has actually made it harder for people to get around. We drive farther, more frequently, and for longer periods than we used to. Research confirms Mayhew’s experience; in 1999, Washington, D.C., residents were driving 77 percent more than they were 1982. Nearly all the increase was due to sprawl and not simply population growth.

An Unhealthy Environment

Sprawl is also compromising human health. Motor vehicle exhaust contains carbon monoxide, smog precursors benzene and formaldehyde, and soot and other particles that are toxic to drivers and people living and working in airflow distance from well-trafficked roads. Recent sprawl studies are revealing surprising health connections, like the fact that children living near high-traffic roadways are more likely to be hospitalized for asthma and six times more likely to develop cancer. A recent report also found that increases in ozone levels from car, industry, and power-plant pollution were associated with increases in death rates in populous U.S. cities.

Choosing to drive versus walking or biking is also contributing to the nation’s obesity epidemic. A recent study in the American Journal of Health Promotion discovered that people living in sprawling communities are more likely to be overweight and have high blood pressure.

Smart Growth

The day-to-day realities of sprawl and the scores of statistics that measure its effects are encouraging some humans to reverse the trend. Community planners nationwide are espousing policies of smart growth, a widely touted brake to accelerated sprawl. Smart growth favors creating neighborhoods with a combination of housing types, communities with services and stores in easy reach of homes, a multitude of clean and efficient transportation options, and preserved open space and critical ecological areas. Effectively implementing smart growth and fostering a more natural, navigable, and survivable habitat for all species, is perhaps one of Homo sapiens’ toughest environmental challenges.

F15 has no tail, only three legs, and a transmitter with a 30 cm long antenna epoxied to her back. Considering F15 is a turtle—and one who must regularly cross a well-trafficked country road to find food and lay her eggs—missing a foot sounds like a cruel twist of fate.

But F15’s battle scars are par for the course. After all, at possibly 50 or 60 years old (in both people and turtle years), she’s been through her share of raccoon sneak attacks and near-misses with plough blades in her habitat—the streams, hayfields, woodlands, and backyards of the rapidly suburbanizing, formerly agricultural Connecticut River valley.

Mike Jones, a biology graduate student at the University of Massachusetts at Amherst, has been following F15 and 52 of her shelled compatriots in the most comprehensive study yet of the habitat use and range of Clemmys insculpta, or wood turtle. The species is of conservation concern in Massachusetts and most of the 16 U.S. states and 4 Canadian provinces it calls home. For the last nine months, Mike has been tracking F15’s whereabouts twice a week via radio transmitter. And he can tell you, unequivocally, that she has not been flattened by an SUV. Yet.

 “The new homes, businesses, and malls that we associate with urban sprawl are connected via roads,” says Paul Sievert, a U.S. Geological Survey ecologist and lead researcher on the wood turtle study. “This fragments the habitat into smaller pieces and increases the traffic rate on the roads currently in existence. There’s not enough time for a turtle to cross the road.” 

The research is intended to provide a clearer picture of how much and what kind of space wood turtles need to survive, and to determine whether existing populations can surmount pressures from sprawl and persist in perpetuity. Jones’s and Sievert’s work will eventually guide a Division of Fisheries and Wildlife conservation plan to protect wood turtle habitat in Massachusetts, a state with some of the tightest environmental laws in the country.

Keep on Truckin’

In less than a hundred years, wood turtles have dwindled from common to fairly scarce in their historic range, which spans the Great Lakes region, New England, and southern Canada. “In New England in the 1800’s, people recorded that they went out with their horse and buggy, and in an afternoon picked up a hundred wood turtles,” says Sievert. “Fast-forward to today. If you find a wood turtle at all, it’s usually a road-killed wood turtle.”

Wood turtles spend most of their days swimming in, basking in, and exploring one cold, brisk stream for their entire lives. The study area in this case is the headwaters of one of the Connecticut River’s 38 main tributaries. Still, the reptiles leave the river regularly to forage for amphibian eggs at vernal, or temporary, pools in adjacent woodlands or to lay eggs in warm, sandy upland sites.

To trail the exact moves of each turtle, Jones uses dental acrylic to affix a transmitter and coiled antenna onto the shell. He programs a handheld receiver to pick up each turtle’s personal signal. Suited in fisherman’s waders and paddling a canoe, Jones relocates each turtle about twice a week during the spring, summer, and fall, noting its GPS location, surrounding habitat, and behavior. “Eventually we’ll be able to measure each turtle's habitat selection on a very large scale,” he says.

It's Not Easy Being Green. Er, Brown and Orange.

During their meanderings, turtles are almost sure to encounter a road, or two, or three. That’s because humans like to build roads parallel to river edges, as construction is much easier along flat riverbeds. Turtles often travel perpendicular to rivers, which usually entails dodging tires.

While roads affect many species, this geometry can be especially devastating for some reptiles, which bank on the high survival rate of adults, rather than juveniles, to maintain their populations. Unlike the super-fecund hare, female wood turtles lay just a single clutch of about 10 eggs a year. Only a small percentage of the eggs hatch, and only a fraction of the hatchlings endure the dangers of raccoons and tractors and tarmac to reach adulthood at age 17. These survival odds, plus the fact that turtles have an impressive number of potential breeding years (some can live over a century) mean that adult turtle loss can seriously affect a species. “One study predicted that if two turtles were lost from a population annually,” says Jones, “the whole population would be lost in less than a hundred years.”

To compound the problem, Jones has learned that females ramble much greater distances from the river than do male turtles—sometimes 500 m to either side. Females, then, are more likely to encounter a road, which suggests that they are dying at a much faster rate than males. “Which is terrible,” says Jones. “You could keep a population around with fewer males for much longer than you could with fewer females.”

Unfortunately, human pressures—and fancies—take their toll on turtles in ways other than vehicular, namely via the pet trade. Wood turtles are particularly noted for their personality (In 1952, landmark herpetologist Archie Carr wrote in hisHandbook of Turtles: “For all who have kept them are agreed that the wood turtle makes a better pet than any other [turtle] species.”). Today, however, capturing wild turtles as pets is illegal throughout the country.

Still, “poaching of turtles for the pet trade and collection of animals by recreationists continues to remove wood turtles from the wild,” says Sievert. “This can decimate local populations.” The effect on the population is exactly the same as if the turtle were killed on a highway.

What’s Around the Bend?

 “Many people are convinced that the ideal situation is to have their home out in the woods,” says Sievert. “But if wildlife had a vote, they’d choose for humans to stay concentrated in urban centers rather than spreading ourselves out in a sprawling suburban environment.”

Sievert suggests that one long-term solution for the reduction of sprawl and its impact on wildlife would be for human population growth to reach zero. In the meantime, wise planning that incorporates the needs of wildlife—such as state-driven land purchasing, conservation easements, mitigation measures like road underpasses for turtle travel, or limiting development—could go a long way in reducing animal mortality and increasing population viability for threatened species in the United States.

Jones adds that the fate of wood turtles is representative of the fate of many creatures in wetland habitats, which are under particular attack by sprawl. “This species was clearly meant to be present throughout New England,” he says. “That was the case for probably the last six or eight thousand years. They have the right to go on existing here.”accordion

Seeds can’t move by themselves, so they rely on moving things to give them a lift. Some catch rides on rivers or gusts of wind. Others cling to pant or dog legs using barb-tipped hairs. Some are eaten and expelled by birds or bats. But the quickest route to world domination, for plants at least, may be via rapid, efficient, and pervasive hitchhiking on enameled steel, radiator grilles, and muddy tires. The increasing urbanization of natural lands, aided and abetted by the automobile, is taking homespun seed dispersal mechanisms to a new level.

Take the Western states’ yellow starthistle (Centaurea solstitialis), for example. This yellow-bloomed, spiny, nonnative weed produces two kinds of sesame-sized seeds, one with bristles, one without. The unbristled seeds catch gravity, dropping within half a meter of the parent plant. The bristled seeds go perhaps three meters better by catching wind currents. Yet since yellow starthistle’s introduction during the gold rush as a contaminant in bags of Chilean alfalfa seed, the plant has managed to carpet 15 million acres of roadside, rangeland, farmland, and grassland in California, mostly by hitching rides on tractors, road maintenance vehicles, and passenger cars. The plant has now invaded 23 states and is northern and central California’s thorniest weed problem, costing the state countless millions in lost grazing land, plummeting ranch revenues, and increased water conservation costs. Overall, the damage and control costs inflicted by invasive species in the United States amount to $138 billion dollars a year.

The spread of development in the United States is tough on many plants and animals. The National Wildlife Federation recently announced that at least 553 of the nation’s most at-risk species are found only in the 35 fastest-growing metropolitan areas. But some species, like yellow starthistle, actually get a population boost from sprawl. These invasive plants—nonnative species that enter an area, outcompete local vegetation for resources, and cause harm environmentally or economically—may even prefer that odd habitat located parallel to the nation’s nearly 6.4 million km of public roads.

Have Seeds, Will Travel

A road’s impact on soil, water, plants, and animals can extend 100 m on either side the pavement, meaning that the country’s public road system has an ecological effect on about one-fifth of all land in the United States. “Roads are the entry point for virtually every human impact on natural systems,” says conservation biologist Jonathan Gelbard, who has conducted a number of studies on how roads affect vegetation.

The habitat alongside a street is by its very nature disturbed, which can cause and accelerate plant invasions. During road construction, the roadsides are usually cleared of their variety of native species in favor of homogenous grass and other nonnative landscaping. Roadsides are also frequently flooded with sun, wet with runoff, compacted, salty, mowed, and replete with car emissions like nitrogen, which acts as a fertilizer. Many opportunistic invasive plants find such unsavory conditions optimal for quick growth. Furthermore, as Gelbard’s research has shown, the more improved the road surface, the more invasives crowd its edges.

After taking root, invasive weeds can swiftly populate the roadside strip. For example, Gelbard analyzed 1,300 sq km of grassland near Napa County, California, and discovered yellow starthistle in 73 percent of areas 10 m from roads, but in only 21 percent of areas further than 1,000 m from roads. Starthistle disperses easily along roadsides by lofting on the high-speed, turbulent wind tunnels generated in road corridors by passing vehicles, or by riding vehicles themselves. After one Montana researcher drove through several feet of knapweed, a starthistle cousin, the car picked up 2,000 seeds and deposited all but 200 of them within 16 km.

Roadside maintenance also aids one of starthistle’s growth strategies. In early spring, while grasses and other roadside plants are sending up young shoots, yellow starthistle lays low—literally hugging the ground with a fledgling, palm-sized rosette—and quickly sends down an extensive root system that can access deep water sources. “Roadside mowers come when the grass is still green,” says Gelbard. “The mowers will blade off the grass but leave the starthistle to flourish in the absence of competition.”   By late May, starthistle bolts up into a tall prickly stalk with yellow flowers framed by 2 cm long spines. The dense spreads of starthistle have the potential to meander into adjacent wild lands, farms, and pastures, leaving landowners to bear the costs of controlling or eradicating the invader.  “By putting off highway mowing for just two or three weeks they could help reduce the problem by mowing the starthistle stalks themselves, says Gelbard.”

Paving Paradise

To keep pace with development, which consumes 2 million acres of wild land per year, transportation agencies consistently add and expand the nation’s road network. Nearly 70,000 lane-kilometers were steamrolled in 2003 alone. But a great many are not part of the 6.4 million km estimate, including the 600,000 km of National Forest roads and untold hundreds of thousands of kilometers of improved and unimproved “ghost roads” for private, military, and ranch use, oil and gas drilling, and other uses. Gelbard singles out those unofficial tracks for four-wheel drive recreation as a serious yet underestimated vector for plant invasion. “Because off-road vehicles go far from roads,” he says, “they not only affect habitats near roads that are already disturbed, but also remote, roadless habitats that are a lot less invaded.” How far invasives are actually creeping from roadsides into interior lands is still unclear and little studied.

Gelbard is hesitant about road expansion as a whole. “By curtailing and limiting the spread of roads,” he says, “you are essentially sealing off corridors from multiple environmental problems and the economic impacts they bring.” While reining in the pavers is unlikely to happen anytime soon (In December 2004, Texas launched the first phase of construction of the Trans-Texas Corridor, a 6,500 km megahighway project with lanes up to a half a kilometer across), recent years have seen ecologists, geographical information specialists, transportation planners, and conservationists take notice of the new field of road ecology. Its science is cross-disciplinary, exploring roadside vegetation, roadkill mitigation, and water, sediment, and chemical flow. It gives roadside habitats their proper due as unique environments. State and federal agencies are also increasingly incorporating ecological concerns into transportation planning, such as the Transportation Research Board’s Task Force on Ecology and Transportation, which links leading road ecologists with transportation planners. Can our desire for mobility work in concert with the needs of the environment? The answer lies down the road.

Not unless you were the last lion on Earth!”

When P1, an adult male mountain lion who roams the 620 sq km Santa Monica Mountains just outside Los Angeles, took stock of his mating options last summer, his pickings were slim. As far as ecologists are aware, his choice, P2, may have been the only female in existence in the entire range.

There are other fish in P1’s sea, which is a chain of protected areas to the north of the coastal range. But P1 can’t get to these areas easily. A six-lane freeway, U.S. 101, divides the Santa Monicas from the gently sloping Simi Hills directly to the north. Above the Simi Hills, Highway 118 bars safe passage into the Santa Susana Mountains. Finally, for P1 to get from the Santa Susanas to the lion-dotted paradise of Los Padres National Forest, a vast coastal range that reaches nearly to the Bay Area, he would have to seek out and sneak through green corridors of undeveloped land perhaps just 20 m wide.

However reluctantly paired, P1 and P2 produced four lion cubs in late August, according to Seth Riley, a National Park Service wildlife ecologist who has been tracking the two via radio and GPS collars for two and a half years. But Riley and other scientists and conservationists worry that the Santa Monica range is too small for at least six lions to coexist and reproduce. In fact, in crowded California, sprawl is now the main threat to 66 percent of the state’s 286 endangered species.

Many believe that the animal-friendly antidote to California’s urbanization is to make the corridors—called linkages—between disparate patches of wild lands truly useable by many different species. Currently, the South Coast Missing Linkages Project is taking the charge seriously. They are working to identify, unite, and protect Southern California’s 15 most threatened habitat connections before new development encroaches. Establishing a crossing at Highway 101 is among the project’s highest priorities.

A Home on the Range

As far as cougar habitat goes, the Santa Monicas aren’t half bad—literally. About 300 of its 620 sq km of craggy, scrub-and-oak-dotted mountains remain open to development, which is still sparse despite continuous pressure from Los Angeles’s ever-eager appetite for housing. “At this point,” says Riley, “there seems to be quality habitat and plenty of deer to eat.”

While P2 requires only about 100 sq km of land, P1’s space needs—about 400 sq km— gobbles up nearly the entire Santa Monica range. “Adult male lions don’t tolerate a lot of other adult males in their area,” says Riley. Since male mountain lions, like all cats, do not raise their young, it’s unlikely that P1 would recognize his two sons, and he may even eliminate this competition. “Certainly they’ll fight,” says Riley. ”Sometimes they’ll even kill each other.”

All told, Riley predicts, the Santa Monicas can support fewer than 10 lions. “But 10 lions is not a population,” says Riley. “For genetic and demographic reasons, that’s just not enough.” Inbreeding, and therefore genetic mutation and disease, increases when populations of large carnivores like cougars, bears, wolves, and wolverines become isolated by development and agriculture. Such problems have sidelined Florida panthers, a subspecies of mountain lion, whose population has been hovering near 50 for decades. Since 1988, Texas cougars have periodically been introduced to Florida to increase genetic diversity.

It’s possible that the young male cougars could seek genetically novel mates in the Simi Hills and beyond by crossing 101 where the scrubby foothills dip slightly, a spot called Liberty Canyon. Here, an underpass exists for a 1.6 m wide drainage culvert and a two-lane road that leads, eventually, to a housing development. Save for an office park and a few other buildings, the vista on both sides of the canyon is natural—a virtue that makes Liberty Canyon one of the two remaining likely animal exits out of the Santa Monicas. P1 and P2 are tracked regularly (once an hour at times), but they have yet to cross over or under 101. P3, a young male who prowls the Simi Hills, has not crossed from the north side of this freeway, either. 

Los Padres or Bust!

As with turtles, the loss of a few individuals can significantly harm entire populations of big predators, since they live longer and reproduce less than most animals do. While scientists remain unclear about exactly what ecological effects a significant loss of cougars could have on the California chapparal community, most scientists agree that animals near the top of the food chain play an important role in biological communities—and in conservation. “Big predators represent the ultimate challenge,” notes Riley. “If we’re able to conserve enough land for them, we’ll potentially be able to conserve most things in their habitat. Plus, big predators are a powerful symbol of wilderness and effective stewardship of lands.”

For these reasons, “the mountain lion is a focal species in every one of our 15 linkages,” says Kristeen Penrod, executive director of South Coast Wildlands, which manages the Missing Linkages effort. Right now, the project is collaborating with the National Park Service, the California Department of Transportation (Caltrans), the Nature Conservancy, and other private and public groups to make Liberty Canyon navigable by lions, deer, bobcats, and other species. The linkage’s first priority, securing the slopes on either side of the canyon from further development and revegetating bare spots, has already been accomplished. In the future, Caltrans may widen and vegetate part of the 101 underpass for both vehicular and quadruped use, install a vegetated land bridge over the highway, or both. Similar suggestions are being considered to enhance connectivity along each link of the entire fragmented land chain from the Santa Monicas to Los Padres National Forest.

“If all 15 of Southern California’s priority linkages were protected, we’d really have the backbone of a regional conservation strategy in place,” says Penrod. “Our project partners want to see our methods used throughout the rest of the state.” Or, perhaps, the nation. In its wildest dreams, the Wildlands Project, a national group working throughout the continent, hopes to reconnect a 6,500 km swath of land along the Rocky Mountains from Canada’s Yukon through Mexico’s northern Sierra Madre. While it’s unlikely that the mountain lion will ever regain its historic range, which was once nearly all of North and South America, getting it safely across the street is, at least, a start.