Road ecology is a relatively new subdiscipline of ecology that focuses on understanding the interactions between road systems and the natural environment. Road ecology is an applied science, and much of the work within this field endeavors to find ways to minimize the detrimental effects that road systems can have on plant and animal populations, air and water quality , and human communities. The body of knowledge generated by studies of the ecological and societal effects of road systems also inform many of the current visions of sustainable development. Other highly visible outputs of road ecology include advances in the management of stormwater runoff, transportation and land-use planning, and the development of crossing structures that allow animals safe passage across busy roads.
Road ecology incorporates elements from and contributes knowledge to many other scientific disciplines. The principles of landscape ecology form the theoretical basis for most studies within road ecology, but road ecology as a science also borrows heavily from conservation biology and fish and wildlife biology. Indeed, because it has yet to develop its own body of theory, much of the work conducted under the rubric of road ecology might also be claimed by a number of other ecological disciplines.
History of road ecology
Studies of the impact of roads have existed as long as roads themselves. Early work focused on the threat that motor vehicles posed to wildlife, and many prominent American naturalists published tallies of road-killed animals encountered during their travels. Broader considerations of the role that roads can have on ecological processes were largely ignored until the latter half of the 20th century, despite the great boom in road construction that took place in much of Europe and North America between 1920 and 1960. The first inklings of what is now called road ecology stem largely from the work of European scientists, most notably Heinz Ellenberg, and transportation ministries in countries such as the Netherlands, Germany, and France. One of the significant realizations of this early work was that road systems could fragment habitat and restrict the movement of animals, a theme that has continued to be a principal focus within road ecology. Accompanying advances in techniques to mitigate the effects of roads of wildlife also emerged from Europe at this time, and were belatedly adopted in parts of the United States (for example, underpasses for Florida panthers along Interstate 75) and Canada (numerous wildlife crossing structures over the Trans-Canada Highway in Banff National Park). The 1990's witnessed an increasing number of studies examining various effects of roads, including a unique line of research by Australian scientists that examined the potential for road rights-of-way to serve as a vast, linear network of conservation lands. During this time, Dutch researchers also began presenting results that suggested traffic noise might have profound and far-reaching effects on bird populations. This realization encouraged a shift in the way road effects were evaluated, from one focused largely on direct effects on the environment immediately surrounding the road to one that encompassed the possibility of indirect effects on areas far removed from the road. The seminal moment in the modern incarnation of road ecology was the publication in 2003 of "Road Ecology", a multi-authored volume that summarized the state of the science.
Elements of road ecology
The science of road ecology is concerned with understanding how roads affect ecological processes, often with the goal of developing strategies for mitigating any negative effects that roads may have on the environment. Although potentially extremely broad in scope, road ecology at present is focused primarily on documenting and predicting the effects of roads on plants and animals and in understanding how roads affect the movement of water and sediments.
Effects of roads on fish and wildlife
The potentially harmful effects that roads may have on wildlife populations have been detailed in the scientific literature since at least 1925, when an article entitled "The Toll of the Automobile" appeared in Science. This paper provided an accounting of the number of road-killed animals observed during a car trip, and raised concerns that the increased mortality caused by collisions with motor vehicles might pose a significant problem for some populations of animals. Many similar papers soon followed. Understanding the effects of roads on wildlife, and more recently fish, continues as a central theme in road ecology, although current work focuses more broadly on understanding how roads constrain the movement of fish and wildlife, and what forms of mitigation can be applied to ameliorate these constraints. Other ongoing avenues of research include studies of the indirect effects of roads on fish and wildlife, such as facilitation of land-use changes or disturbance caused by traffic noise or artificial street lighting.
Most roadside plant communities are managed to enhance visibility for motorists, minimize risks for vehicles that leave the roadway, reduce erosion and sediment flow, and provide an aesthetically pleasing vista for travelers. In some cases, roadsides are also managed for the benefit of rare plants or as corridors for wildlife movement. Studies in road ecology contribute to this effort by elucidating the processes that shape the structure and composition of roadside plant communities. For example, road ecologists have addressed questions such as how frequently roadsides must be mowed to maintain desired conditions, the role that roads play in promoting the spread of invasive weeds, and how best to revegetate the bare soil left behind after construction projects.
Effects of roads on the movement of water and sediments
Roads have a pronounced effect on the movement of water, acting both as conduits and barriers. For example, a road cutting across a hillside may force surface and subsurface water to move laterally, rather than downslope. Barrier effects such as these are even more pronounced when roads bisect wetlands. Roads, because they are generally surfaced with impervious materials, can also intercept and divert precipitation, which can result in altered hydrological patterns in natural drainages. The effect that roads have on the movement of water also influences the movement of the material transported by water; for example, roads can accelerate scouring in natural drainages by increasing peak flows through delivery of stormwater runoff (thereby increasing the ability of the water to suspend and move sediments). Roads also influence sediment movement simply by creating areas of bare soil (for example, unvegetated cut or fill slopes or unpaved road surfaces) that are vulnerable to erosion. The changes in water and sediment flow patterns caused by roads have potentially significant effects on aquatic ecosystems, and studies seeking to document and understand these effects comprise a large portion of the existing body of literature on road ecology. Current focal areas include development of new techniques to manage stormwater runoff (for example, permeable pavements and roadside bioretention swales) and continuing studies of how stream crossings influence water and sediment flows, especially as they affect conditions for spawning and migrating fish.
- Forman, R. T. T., D. Sperling, J. A. Bissonette, A. P. Clevenger, C. D. Cutshall, V. H. Dale, L. Fahrig, R. France, C. R. Goldman, K. Heanue, J. A. Jones, F. J. Swanson, T. Turrentine, and T. C. Winter. 2003. Road ecology: science and solutions. Island Press, Washington, D.C., USA.
- Stoner, D. 1925. The toll of the automobile. Science 61:56-57.