Road Ecology

Science and Solutions

Richard T.T. Forman,Daniel Sperling,John A. Bissonette,Anthony P. Clevenger,Carol D. Cutshall,Virginia H. Dale,Lenore Fahrig,Robert L. France,Charles R. Goldman,Kevin Heanue,Julia Jones,Frederick Swanson,Thomas Turrentine,Thomas C. Winter

• Publisher: Island Press
• Year: 2013
• ISBN:
  9781610913171
• Topic: Architecture
• Subtopic: Architecture General

A central goal of transportation is the delivery of safe and efficient services with minimal environmental impact. In practice, though, human mobility has flourished while nature has suffered. Awareness of the environmental impacts of roads is increasing, yet information remains scarce for those interested in studying, understanding, or minimizing the ecological effects of roads and vehicles.

Road Ecology addresses that shortcoming by elevating previously localized and fragmented knowledge into a broad and inclusive framework for understanding and developing solutions. The book brings together fourteen leading ecologists and transportation experts to articulate state-of-the-science road ecology principles, and presents specific examples that demonstrate the application of those principles. Diverse theories, concepts, and models in the new field of road ecology are integrated to establish a coherent framework for transportation policy, planning, and projects. Topics examined include:

• foundations of road ecology
• roads, vehicles, and transportation planning
• vegetation and roadsides
• wildlife populations and mitigation
• water, sediment, and chemical flows
• aquatic ecosystems
• wind, noise, and atmospheric effects
• road networks and landscape fragmentation

Road Ecology links ecological theories and concepts with transportation planning, engineering, and travel behavior. With more than 100 illustrations and examples from around the world, it is an indispensable and pioneering work for anyone involved with transportation, including practitioners and planners in state and province transportation departments, federal agencies, and nongovernmental organizations. The book also opens up an important new research frontier for ecologists.

PART I

Roads, Vehicles, and Ecology

CHAPTER 1

Foundations of Road Ecology

What is the use of running when we are not on the right road?

—German proverb

. . . great technical advances occurred in the technology of pavement structures and surfacings during the nineteenth century. Almost in their entirety, these advances predated the development of the motorcar.... Communities at last saw an alternative to a life full of mud, stench, dust, and noise.

—M. G. Lay, Ways of the World, 1992

Transportation lies at the core of society. It is what links us together. Both businesses and individuals depend on safe and efficient mobility. In the past century in North America, roads and vehicles have enlarged the spiderweb of our interactions and activities. Now we routinely use vehicles on roads to visit a friend, go shopping, travel to school, or dine out.

Unfortunately, with this dependence on roads and vehicles comes deep and widespread environmental damage. ^{674, 675} As a result, environmental protection now plays a key role in transportation policy and decisions. Ever-increasing resources are devoted to minimizing the adverse impacts of roads and vehicles on species and ecological systems.

Environmental protection is viewed and approached from many perspectives. The engineer seeks technical solutions and designs technical devices to abate damages. The economist seeks the best use of societal resources and identifies actions that yield the highest return. Legislators and lawyers craft sharply defined rules to preclude certain behaviors. Ecologists emphasize that we are too human centered in our responses and seek to elevate the importance of plants and animals. They seek to maintain the diverse characteristics and services of intact, or undegraded, nature and to maintain or reestablish relatively natural ecological systems in human-imprinted areas. Meshing this goal with the economic and social activities of our busy highways remains a daunting challenge.

What’s Nature Like Near a Busy Highway?

Consider taking a leisurely stroll or nature walk in the edge of woods by a busy two-lane highway.⁶⁷⁵ The sense of leisure quickly evaporates in the face of traffic noise. Speeding vehicles evoke a sense of danger.You may be confronted underfoot with society’s refuse. Busy roads and a bucolic outdoors seem incompatible.

So you move back into the wooded edge to look more closely. Many of the native forest birds seem to be missing—even for quite a distance into the forest; apparently it is too noisy. Indeed, few other forest vertebrates—mammals, frogs, turtles, snakes—are seen; it must be a road-avoidance zone for them, too. If you had ventured to walk along the roadside, you might have seen road-killed animals, though carcasses disappear quickly where road-kill scavengers hunt. The combination of road-avoidance zone and road-kill strip makes you realize what a barrier the busy highway is, dividing large natural populations into small ones that may be prone to local extinction. Also, wildlife movement corridors that connect distant patches across the landscape may be severed.You wonder whether this is an inadvertent collective assault on biodiversity.

Unlike the adjoining forest interior, your forest edge seems to be full of generalist “weedy” plants, some of them non-native exotics, all persisting next to the open environment of a frequently mowed roadside. The road-side vegetation growing on earth that was homogenized and smoothed during road construction seems monotonous, largely devoid of its natural heterogeneity and richness. A few grasses, plus some non-native plants, tend to dominate at the expense of a diversity of native wildflowers. Open, straight roadside ditches carry warmed water, alternating with pulses of rainwater, into a narrow, wooded stream that lost its valuable curves during road construction. A specific set of invisible chemicals has reached the roadside and perhaps the forest—nitrogen oxides, hydrocarbons, herbicides, roadsalt, and heavy metals such as zinc and cadmium are typical. Entering the streams, wetlands, and groundwater around you, they inhibit all kinds of natural processes and are toxic to some of the species.

What is it like next to a busy road? No place for a neighborhood walk. Or a path in a park. Or even a nature reserve. Here nature is both severed and impoverished. Road ecology is needed.

In market economies, prices are a primary mechanism for allocating resources and guiding behavior. Environmental impacts remain largely outside the marketplace. ²⁰⁰ When we drive a car, we degrade the quality of everyone’s air. But we do not pay for damage to health or vegetation. If we did, we would probably pollute less. Although conceptual models exist, no effective mechanism in society ensures a proper balance between supply and demand for clean air. The same basic problem exists for noise and water pollution, climate change, aesthetics, loss of wetlands, and loss of biological diversity. The absence of a pricing mechanism has led to regulatory approaches.

Environmental protection is complex yet more easily regulated in transportation than in most other sectors of society because transportation networks are mainly in the public domain. Governments at various levels build and maintain most roads and largely own, operate, and subsidize transit services. Governments also own and manage many ecologically important lands where public roads exist (Figure 1.1). Entwinement of transportation with the public domain means that public goals, such as environmental protection, play a more direct role in investments and institutional behavior. Public pressure can translate directly into action by elected leaders and public officials.

Figure 1.1. Government land, where a state- and federally funded road and nongovernment vehicles interact with a sequence of species and ecosystems in a national forest. Design of the road included varying the edges of tree lines to eliminate straight lines; reducing slope angles and varying cut-and-fill slopes to eliminate flat planes; creating rock outcrops similar to native ones; and planting only erosion-control grasses so that natural plant succession follows. State Route 410, Snoqualmie National Forest, Washington. Courtesy U.S. FHWA.

Environmental protection came to the forefront of public discourse in the 1960s. Such environmental disasters as London’s “killer smog,” which killed scores of people, and the Cuyahoga River in Ohio (USA), which caught fire, galvanized worldwide attention. The realization that newly developed and widely used chemicals could decimate ecosystems and poison humans on an extensive scale, a discovery highlighted by Rachel Carson’s Silent Spring, catalyzed public action.

In the transportation sector, air pollution proved the initial and most compelling call to action, first in California and then elsewhere.⁶⁷⁴ Widespread pollution in the USA culminated with the federal 1970 Clean Air Act, which accelerated the process of eliminating lead from gasoline and reducing vehicular pollution.This law was followed in the mid-1970s by fuel economy rules and “gas guzzler” disincentives. Japan pursued roughly the same track in reducing emissions and fuel consumption, as did Western Europe somewhat later.

In a larger sense, many nations were becoming more environmentally conscious as the 1960s ended. Rules and laws were passed to reduce noise and decrease air and water pollution. Greater concern for aesthetics was emerging. In the USA, the National Environmental Policy Act (NEPA) became law, which required that environmental impacts be documented for new projects using federal funds. By the 1970s, environmental and aesthetic concerns were beginning to play an important, if not always well informed, role in the design, construction, and operation of roads.

But even as environmental consciousness evolved, knowledge and political will lagged. As one concern was addressed, another would emerge.⁶⁷⁵ As road-side aesthetics received greater emphasis, concerns about non-native and invasive species grew. A phalanx of new rules and institutions emerged to control a carefully specified set of air and water pollutants. But new threats from new pollutants kept appearing. As four-wheel-drive and other high-clearance vehicles tended to replace cars, remote natural areas became accessible to recreational vehicles, and telecommuting from rural areas gained appeal, the threat to ecologically sensitive land increased.

Furthermore, environmental impacts have become global in nature, through the cascading accumulation of ecological stresses and altering of ecological interactions of the earth system itself.^{428, 674} The pervasiveness of roads and their cumulative effect on the environment are now of increasing concern for habitat fragmentation, rare species, and aquatic ecosystems.

What Is Road Ecology?

In 1994, a lone ecologist slowly drove a long, winding road up a canyon in the Rocky Mountains. Front views, like an ancient movie, flashed back and forth from towering granite cliffs to precipitous forest slopes. The road, an engineering marvel, crept over old landslides, and the car sidled past avalanche tracks.The destination was a conference of the Ecological Society of America, where 2500 ecologists were packed into the canyon. Upon arrival, the driver, who sensed that road ecology might be important but had never heard of a meeting on the subject, studied the printed program of over 2000 presentations. The word “road” appeared in only one title. He talked with people, from world authorities to promising students. Everyone could speak knowledgeably, even passionately, about the unusual birds around, how to measure the vegetation, the water flows, erosion patterns, wildlife trails, and mathematical models. No one mentioned that omnipresent road running through the canyon.

The ecologist then walked up the canyon to look more closely. The serpentlike route through the heart of the valley was the organizing force for almost all human activities. Hordes of early miners had used it as access to their dreams of wealth, and tens of thousands of sheep must have been shepherded up and down the canyon every year along this solitary route. Bandits and predators lined the route.Today, hotels and tourists, ski areas, homes, and everything else human depend on the condition of that lifeline. But what about those birds and vegetation and water flows and erosion patterns and wildlife movements ? Do they affect the road? Or does the road affect them? Indeed, how does life change for plants and animals with a road and traffic nearby?

Answering these questions, and similar ones from local spots everywhere, leads inexorably to road ecology. Indeed, a handful of key concepts and terms here helps bring the big picture into focus.

A road is an open way for the passage of vehicles,^{1015, 532} and ecology is the study of interactions between organisms and the environment .^{856, 776} Therefore, the combination describes the essence of road ecology, namely, the interaction of organisms and the environment linked to roads and vehicles. More broadly, traffic flows on an infrastructure of roads and related facilities form a road system. Thus road ecology explores and addresses the relationship between the natural environment and the road system.

Let us delve into that concept to learn more. Roads come in many varieties, from multilane highways to suburban streets, from logging roads to farmers’ lanes (Figure 1.2). All are the focus of road ecology. Sometimes the term “road” or “roadway” refers to the roadbed area between roadside ditches. Other times, road or road corridor refers to a wider strip where the land surface has been altered by construction, maintenance, or management regimes. Commonly, this wider strip includes the road surface, shoulders, ditches, and outer roadsides. Where cutting through the side of a slope, the road corridor typically includes a cut surface on the uphill side and a filled area on the downhill side.² Various engineered structures to control, for instance, water flow or snow accumulation may be included in this wider road strip. A highway corridor usually also includes the strip of cultural structures, as in strip development, associated with the highway.⁹⁹⁵

Figure 1.2. An urban collector-distributor roadway linking major arterial highways with downtown streets. This six- to eight-lane, median-divided roadway carrying high volumes of traffic through changing residential and commercial areas has curbside and median plantings, brick splashblocks, sidewalks, screening walls, and quality light fixtures. Harbor City Boulevard (State Route 720), Baltimore, Maryland. Courtesy U.S. FHWA.

These attributes, and many more that will be discussed later, are useful in describing a road location or site. Road ecology also focuses on a road segment, the stretch of road between two points, such as between two intersections or towns (Figure 1.2). A road segment thus slices through a heterogeneous landscape, so that the pair of adjoining local ecosystems or land uses on opposite sides of the road keeps changing along the segment. The sequence of pairs is little studied but may be ecologically important i...