The Evolution of Road Science
When Wildlands CPR was formed in 1994, the scientific basis linking roads and biodiversity was still rudimentary, although field biologists and conservationists had long been aware of road-related problems such as roadkill, landslides, and pollution. As early as the 1920s, scientists kept track of roadkill rates across the United States, Canada, and Scandinavia, where collisions with large mammals often resulted in human injury or fatalities. Beyond simply counting roadkill, however, little research attention was directed at roads — until recently. This article reviews how research on roads has moved to the forefront of conservation study.
Road Research
During the late 1980s and early 1990s, published research articles began to address roads. Noss (1990) was the first to review the literature on the ecological impacts of roads, however, his article was unreferenced, and published in a journal read by few scientists. He found that aside from the direct problem of animals being struck by vehicles, roads provide access to poachers, contribute sediments and chemicals to water bodies, serve as barriers to animal movements, facilitate invasions of exotic species and pests, create noise, air, water, and soil pollution, and degrade scenic and wilderness qualities of landscapes.
Over the last 10 years, scientists have increasingly recognized the threats roads pose to wildlife and the integrity of ecosystems. In their 1994 book, Saving Nature’s Legacy, Reed Noss and Allen Cooperrider briefly reviewed some of the existing research on roads, this time in a more accessible publication, while supplying references to the peer-reviewed literature. Then, in 1995 Wildlands CPR asked Reed Noss to assemble a bibliography of literature on the ecological effects of roads. Noss began with existing bibliographies: one he compiled in 1987-88 and updated sporadically through 1990; an annotated database on highway modifications for wildlife compiled by Steve Humphrey at the University of Florida; and several journal-specific annotated bibliographies compiled by Paul Paquet of the University of Calgary. Together, these databases formed the first comprehensive collection of road literature.
As the number of peer-reviewed journal articles related to road impacts increased in the 1990s, symposia and entire conferences were dedicated to road research. Two consecutive conferences in Florida were the first to address the impact of roads on wildlife exclusively. In 1996 “Trends in Addressing Transportation Related Wildlife Mortality” took place in Tallahassee; two years later the first International Conference on Ecology and Transportation (ICOET) was held in Ft. Myers. ICOET continues every two years and is “designed to address the broad range of ecological issues related to surface transportation development, providing the most current research information and best practices in the areas of wildlife, fisheries, wetlands, water quality, overall ecosystems management, and related policy issues.”
Additional reviews in the late 1990s revealed the scope of road effects across the United States. Forman and Alexander (1998) reviewed the impacts of roads and found that “based on road-effect zones, an estimated 15-20% of the United States is ecologically impacted by roads.” Riiters and Wichham (2003) similarly reported that over 20% of the U.S. was within 127 meters of a road and that over 80% of the U.S. was within a kilometer of a road.
By the turn of the century, researchers for the U.S. Forest Service (who manages almost a half-million mile road system) were acknowledging the impacts of roads. Gucinski et al. (2001) was the first formal Forest Service review of the impacts of forest roads. The Forest Service has started closing and removing roads. Additionally, the U.S. Department of Transportation has reviewed the impacts of their roads and has begun to mitigate their sprawling highway system for wildlife and human safety (e.g. USDOT 2000, USDOT 2004).
Mitigation Science
As it has become more apparent that roads are having a biologically significant effect on wildlife in many areas, research on wildlife crossings and other road mitigation has mushroomed. Europeans have built crossing structures for decades to mitigate the barrier effects of roads on small mammals and amphibians. They have successfully used underpasses to channel small mammals and amphibians under roads (e.g., Langton 1989, Friedman 1997). Europeans have also built dozens of wildlife overpasses and have studied the effectiveness of different mitigation techniques for more than a decade (e.g. Van Wieren and Worm 2001).
In the 1970s North America saw its first wildlife crossing structures built. In Colorado and other western states, migrating mule deer suffer considerable mortality trying to cross highways; collisions between deer and vehicles also injure motorists. In 1970, the Colorado Division of Highways constructed a 10-by-10-foot concrete tunnel under Interstate 70 west of Vail for use by mule deer, and used fences to funnel deer to the underpass. A study by the Colorado Division of Wildlife confirmed that hundreds of migrating mule deer used the tunnel but also suggested that larger and more open underpasses would be more appealing and result in greater rates of deer movement (Reed et al. 1975).
In southwestern Utah, a narrow bridge (8 meters wide) enhanced deer movement along a ridge. In northern New Jersey, two wider overpasses (30 meters wide) were constructed for horseback riders and deer after a multilane highway cut a park in two (Kuennen 1989). In Banff National Park, Alberta, several overpasses have recently been built, some of which are more than 50 meters wide. Researchers have found that large and rare carnivores, as well as a number of ungulates, are using the overpasses (e.g. Clevenger and Waltho 2000, 2004; Gloyne and Clevenger 2001). In Florida a wildlife overpass built in 2000 allows deer, foxes, coyotes, opossums, and other animals to cross over I-75. Unfortunately, this overpass is too narrow to accommodate larger, more sensitive species such as black bear or panther (R. Noss, pers. obs.).
As our highways become wider and carry more traffic, and as our wildlands decrease in size and become more isolated, wildlife overpasses will increase in importance. For example, a proposed wildlife overpass will allow grizzly bears to safely cross Highway 93 (MT) into important habitat. The expansion of grizzly bear range in the U.S. Northern Rockies into the Selway-Bitterroot Wilderness is essential for the continued viability of this population over time (Boyce et al. 2002).
Road Removal Science
In 2002, Wildlands CPR funded a special section on roads in the journal Conservation Biology. In addition to publishing some of the most recent research on roads, this section included one of the first refereed review articles to recommend road prevention and removal. Trombulak and Frissell (2000) concluded that their review “underscores the importance to conservation of avoiding construction of new roads in roadless or sparsely roaded areas and of removal or restoration of existing roads to benefit both terrestrial and aquatic biota.”
Millions of dollars are being spent to remove roads across North America or to mitigate their negative impacts, yet the science of road removal, wildlife crossings, and other mitigation has not kept pace. The limited research on the benefits of road removal to date demonstrates the effectiveness of removal for restoring hydrologic and geomorphic conditions. Switalski et al. (2004) reviewed the literature and found decreases in chronic sediment loss and reduced risk of road-triggered landslides after road obliteration. Similarly, monitoring of wildlife crossing structures has shown benefits in terms of successful wildlife passage (e.g., Clevenger and Waltho 2004), yet few studies have been continued for sufficient time to demonstrate long-term impacts on wildlife along stretches of road with and without crossing structures.
No published study has yet examined how road removal impacts fish and wildlife; a University of Montana study will be the first. A new research project on the Flathead National Forest (MT) is assessing the benefits and impacts of different types of road removal on the threatened bull trout. Also, the first study to examine whether terrestrial wildlife are responding to road removal is taking place on the Clearwater National Forest in ID. Wildlands CPR is a key funder for both of these projects.
Roads in the Context of Conservation Planning
Increasingly, road impacts are considered within the broader context of regional conservation planning. For instance, roadless areas and landscapes with low road densities are recognized in habitat suitability models and population viability analyses as key refugia or source areas for species, such as large carnivores, sensitive to human access and associated legal or illegal killing. In addition, regional conservation planning allows the identification of key areas to implement road closures and wildlife crossing structures, for example in proposed linkages between core areas (e.g., Noss et al. 2002).
Conclusion
Road science has come a long way over the last couple of decades. While once only addressed by a few conservationists and wildlife biologists, road research now is the topic of hundreds of papers, several reviews, large conferences, and an entire text book (Road Ecology, Forman et al. 2003). The problems caused by roads have been well documented, yet more research is needed on how to reverse the impacts of roads through mitigation and road removal. Additionally, roads need to be addressed in a broader context to restore habitat quality and connectivity across North America and beyond.
— Adam Switalski is the Science Coordinator for Wildlands CPR. Reed Noss is the Davis-Shine Professor of Conservation Biology at the University of Central Florida and a contributor to Wildlands CPR’s database. Wildlands CPR continues to promote road science and is guiding road removal research on several national forests. Wildlands CPR also maintains a bibliographic database with more than 10,000 citations documenting the physical and ecological effects of roads and off-road vehicles.
Literature Cited
Boyce, M.S., E.M. Kirsch, and C. Servheen. 2002. Bethedging applications for conservation. Bioscience 27 (supplemental 2): 385-392.
Clevenger, A.P., N. Waltho. 2000. Factors influencing the effectiveness of wildlife underpasses in Banff National Park, Alberta, Canada. Conservation Biology 14(1): 47-56.
Clevenger, A.P., and N. Waltho. 2004. Performance indices to identify attributes of highway crossing structures facilitating movement of large mammals. Biological Conservation (in press).
Forman, R. T. T., and L. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematics 29:207-231.
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, T.C. Winter. 2003. Road Ecology – Science and Solutions. Washington D.C.: Island Press.
Friedman, D.S. 1997. Nature as infrastructure: The National Ecological Network and Wildlife-Crossing Structures in The Netherlands. Report 138. Wageningen, Netherlands: DLO Winand Staring Centre.
Gloyne, C.C., A.P. Clevenger. 2001. Cougar (Puma concolor) use of wildlife crossing structures on the Trans-Canada highway in Banff National Park, Alberta. Wildlife Biology 7(2): 117-124.
Gucinski, H., M.J. Furniss, R.R. Ziemer, and M.H. Brookes. 2001. Forest roads: a synthesis of scientific information. General Technical Report PNW-GTR-509. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 103p. Available online at: http://www.fs.fed.us/eng/road_mgt/science.pdf
Kuennen, T. 1989. New Jersey’s I-78 preserves mountain habitat. Roads and Bridges (February 1989): 69-73.
Langton, T.E.S., ed. 1989. Amphibians and Roads. Shefford, Bedfordshire, England: ACO Polymer products.
Noss, R.F. 1990. The ecological effects of roads. Road-Ripper’s Handbook, ROAD-RIP, Missoula, MT.
Noss, R.F., and A. Cooperrider. 1994. Saving Nature’s Legacy-Protecting and Restoring Biodiversity. Washington D.C.: Island Press. 443 p.
Noss, R.F., C. Carroll, K. Vance-Borland, and G. Wuerthner. 2002. A multicriteria assessment of the irreplaceability and vulnerability of sites in the Greater Yellowstone Ecosystem. Conservation Biology 16:895-908.
Reed, D.F., T.N. Woodard, and T.M. Pojar. 1975. Behavioral response of mule deer to a highway underpass. Journal of Wildlife Management 39:361-367.
Riiters, K.H., J.D. Wickham. 2003. How far to the nearest road? Frontiers in Ecology and the Environment. 1(3):125-129.
Switalski, TA, JA Bissonette, TH DeLuca, CH Luce, and MA Madej. 2004. Benefits and impacts of road removal. Frontiers in Ecology and the Environment. 2(1): 21-28.
Trombulak, S.C., and C.A. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology 14: 18-30.
U.S. Department of Transportation. 2000. Critter Crossings: Linking Habitats and Reducing Roadkill. Federal Highway Administration, Office of Natural Environment. 32p. http://www.fhwa.dot.gov/environment/wildlifecrossings/intro.htm
U.S. Department of Transportation. 2004. Keeping it Simple: Easy Ways to Help Wildlife Along Roads. Federal Highway Administration, Office of Natural Environment. 58p.
Van Wieren, S.P., ans P.B. Worm. 2001. The use of motorway wildlife overpass by large mammals. Netherlands Journal of Zoology 51(1): 97-105.
Road Research
During the late 1980s and early 1990s, published research articles began to address roads. Noss (1990) was the first to review the literature on the ecological impacts of roads, however, his article was unreferenced, and published in a journal read by few scientists. He found that aside from the direct problem of animals being struck by vehicles, roads provide access to poachers, contribute sediments and chemicals to water bodies, serve as barriers to animal movements, facilitate invasions of exotic species and pests, create noise, air, water, and soil pollution, and degrade scenic and wilderness qualities of landscapes.
Over the last 10 years, scientists have increasingly recognized the threats roads pose to wildlife and the integrity of ecosystems. In their 1994 book, Saving Nature’s Legacy, Reed Noss and Allen Cooperrider briefly reviewed some of the existing research on roads, this time in a more accessible publication, while supplying references to the peer-reviewed literature. Then, in 1995 Wildlands CPR asked Reed Noss to assemble a bibliography of literature on the ecological effects of roads. Noss began with existing bibliographies: one he compiled in 1987-88 and updated sporadically through 1990; an annotated database on highway modifications for wildlife compiled by Steve Humphrey at the University of Florida; and several journal-specific annotated bibliographies compiled by Paul Paquet of the University of Calgary. Together, these databases formed the first comprehensive collection of road literature.
As the number of peer-reviewed journal articles related to road impacts increased in the 1990s, symposia and entire conferences were dedicated to road research. Two consecutive conferences in Florida were the first to address the impact of roads on wildlife exclusively. In 1996 “Trends in Addressing Transportation Related Wildlife Mortality” took place in Tallahassee; two years later the first International Conference on Ecology and Transportation (ICOET) was held in Ft. Myers. ICOET continues every two years and is “designed to address the broad range of ecological issues related to surface transportation development, providing the most current research information and best practices in the areas of wildlife, fisheries, wetlands, water quality, overall ecosystems management, and related policy issues.”
Additional reviews in the late 1990s revealed the scope of road effects across the United States. Forman and Alexander (1998) reviewed the impacts of roads and found that “based on road-effect zones, an estimated 15-20% of the United States is ecologically impacted by roads.” Riiters and Wichham (2003) similarly reported that over 20% of the U.S. was within 127 meters of a road and that over 80% of the U.S. was within a kilometer of a road.
By the turn of the century, researchers for the U.S. Forest Service (who manages almost a half-million mile road system) were acknowledging the impacts of roads. Gucinski et al. (2001) was the first formal Forest Service review of the impacts of forest roads. The Forest Service has started closing and removing roads. Additionally, the U.S. Department of Transportation has reviewed the impacts of their roads and has begun to mitigate their sprawling highway system for wildlife and human safety (e.g. USDOT 2000, USDOT 2004).
Mitigation Science
As it has become more apparent that roads are having a biologically significant effect on wildlife in many areas, research on wildlife crossings and other road mitigation has mushroomed. Europeans have built crossing structures for decades to mitigate the barrier effects of roads on small mammals and amphibians. They have successfully used underpasses to channel small mammals and amphibians under roads (e.g., Langton 1989, Friedman 1997). Europeans have also built dozens of wildlife overpasses and have studied the effectiveness of different mitigation techniques for more than a decade (e.g. Van Wieren and Worm 2001).
In the 1970s North America saw its first wildlife crossing structures built. In Colorado and other western states, migrating mule deer suffer considerable mortality trying to cross highways; collisions between deer and vehicles also injure motorists. In 1970, the Colorado Division of Highways constructed a 10-by-10-foot concrete tunnel under Interstate 70 west of Vail for use by mule deer, and used fences to funnel deer to the underpass. A study by the Colorado Division of Wildlife confirmed that hundreds of migrating mule deer used the tunnel but also suggested that larger and more open underpasses would be more appealing and result in greater rates of deer movement (Reed et al. 1975).
In southwestern Utah, a narrow bridge (8 meters wide) enhanced deer movement along a ridge. In northern New Jersey, two wider overpasses (30 meters wide) were constructed for horseback riders and deer after a multilane highway cut a park in two (Kuennen 1989). In Banff National Park, Alberta, several overpasses have recently been built, some of which are more than 50 meters wide. Researchers have found that large and rare carnivores, as well as a number of ungulates, are using the overpasses (e.g. Clevenger and Waltho 2000, 2004; Gloyne and Clevenger 2001). In Florida a wildlife overpass built in 2000 allows deer, foxes, coyotes, opossums, and other animals to cross over I-75. Unfortunately, this overpass is too narrow to accommodate larger, more sensitive species such as black bear or panther (R. Noss, pers. obs.).
As our highways become wider and carry more traffic, and as our wildlands decrease in size and become more isolated, wildlife overpasses will increase in importance. For example, a proposed wildlife overpass will allow grizzly bears to safely cross Highway 93 (MT) into important habitat. The expansion of grizzly bear range in the U.S. Northern Rockies into the Selway-Bitterroot Wilderness is essential for the continued viability of this population over time (Boyce et al. 2002).
Road Removal Science
In 2002, Wildlands CPR funded a special section on roads in the journal Conservation Biology. In addition to publishing some of the most recent research on roads, this section included one of the first refereed review articles to recommend road prevention and removal. Trombulak and Frissell (2000) concluded that their review “underscores the importance to conservation of avoiding construction of new roads in roadless or sparsely roaded areas and of removal or restoration of existing roads to benefit both terrestrial and aquatic biota.”
Millions of dollars are being spent to remove roads across North America or to mitigate their negative impacts, yet the science of road removal, wildlife crossings, and other mitigation has not kept pace. The limited research on the benefits of road removal to date demonstrates the effectiveness of removal for restoring hydrologic and geomorphic conditions. Switalski et al. (2004) reviewed the literature and found decreases in chronic sediment loss and reduced risk of road-triggered landslides after road obliteration. Similarly, monitoring of wildlife crossing structures has shown benefits in terms of successful wildlife passage (e.g., Clevenger and Waltho 2004), yet few studies have been continued for sufficient time to demonstrate long-term impacts on wildlife along stretches of road with and without crossing structures.
No published study has yet examined how road removal impacts fish and wildlife; a University of Montana study will be the first. A new research project on the Flathead National Forest (MT) is assessing the benefits and impacts of different types of road removal on the threatened bull trout. Also, the first study to examine whether terrestrial wildlife are responding to road removal is taking place on the Clearwater National Forest in ID. Wildlands CPR is a key funder for both of these projects.
Roads in the Context of Conservation Planning
Increasingly, road impacts are considered within the broader context of regional conservation planning. For instance, roadless areas and landscapes with low road densities are recognized in habitat suitability models and population viability analyses as key refugia or source areas for species, such as large carnivores, sensitive to human access and associated legal or illegal killing. In addition, regional conservation planning allows the identification of key areas to implement road closures and wildlife crossing structures, for example in proposed linkages between core areas (e.g., Noss et al. 2002).
Conclusion
Road science has come a long way over the last couple of decades. While once only addressed by a few conservationists and wildlife biologists, road research now is the topic of hundreds of papers, several reviews, large conferences, and an entire text book (Road Ecology, Forman et al. 2003). The problems caused by roads have been well documented, yet more research is needed on how to reverse the impacts of roads through mitigation and road removal. Additionally, roads need to be addressed in a broader context to restore habitat quality and connectivity across North America and beyond.
— Adam Switalski is the Science Coordinator for Wildlands CPR. Reed Noss is the Davis-Shine Professor of Conservation Biology at the University of Central Florida and a contributor to Wildlands CPR’s database. Wildlands CPR continues to promote road science and is guiding road removal research on several national forests. Wildlands CPR also maintains a bibliographic database with more than 10,000 citations documenting the physical and ecological effects of roads and off-road vehicles.
Literature Cited
Boyce, M.S., E.M. Kirsch, and C. Servheen. 2002. Bethedging applications for conservation. Bioscience 27 (supplemental 2): 385-392.
Clevenger, A.P., N. Waltho. 2000. Factors influencing the effectiveness of wildlife underpasses in Banff National Park, Alberta, Canada. Conservation Biology 14(1): 47-56.
Clevenger, A.P., and N. Waltho. 2004. Performance indices to identify attributes of highway crossing structures facilitating movement of large mammals. Biological Conservation (in press).
Forman, R. T. T., and L. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematics 29:207-231.
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, T.C. Winter. 2003. Road Ecology – Science and Solutions. Washington D.C.: Island Press.
Friedman, D.S. 1997. Nature as infrastructure: The National Ecological Network and Wildlife-Crossing Structures in The Netherlands. Report 138. Wageningen, Netherlands: DLO Winand Staring Centre.
Gloyne, C.C., A.P. Clevenger. 2001. Cougar (Puma concolor) use of wildlife crossing structures on the Trans-Canada highway in Banff National Park, Alberta. Wildlife Biology 7(2): 117-124.
Gucinski, H., M.J. Furniss, R.R. Ziemer, and M.H. Brookes. 2001. Forest roads: a synthesis of scientific information. General Technical Report PNW-GTR-509. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 103p. Available online at: http://www.fs.fed.us/eng/road_mgt/science.pdf
Kuennen, T. 1989. New Jersey’s I-78 preserves mountain habitat. Roads and Bridges (February 1989): 69-73.
Langton, T.E.S., ed. 1989. Amphibians and Roads. Shefford, Bedfordshire, England: ACO Polymer products.
Noss, R.F. 1990. The ecological effects of roads. Road-Ripper’s Handbook, ROAD-RIP, Missoula, MT.
Noss, R.F., and A. Cooperrider. 1994. Saving Nature’s Legacy-Protecting and Restoring Biodiversity. Washington D.C.: Island Press. 443 p.
Noss, R.F., C. Carroll, K. Vance-Borland, and G. Wuerthner. 2002. A multicriteria assessment of the irreplaceability and vulnerability of sites in the Greater Yellowstone Ecosystem. Conservation Biology 16:895-908.
Reed, D.F., T.N. Woodard, and T.M. Pojar. 1975. Behavioral response of mule deer to a highway underpass. Journal of Wildlife Management 39:361-367.
Riiters, K.H., J.D. Wickham. 2003. How far to the nearest road? Frontiers in Ecology and the Environment. 1(3):125-129.
Switalski, TA, JA Bissonette, TH DeLuca, CH Luce, and MA Madej. 2004. Benefits and impacts of road removal. Frontiers in Ecology and the Environment. 2(1): 21-28.
Trombulak, S.C., and C.A. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology 14: 18-30.
U.S. Department of Transportation. 2000. Critter Crossings: Linking Habitats and Reducing Roadkill. Federal Highway Administration, Office of Natural Environment. 32p. http://www.fhwa.dot.gov/environment/wildlifecrossings/intro.htm
U.S. Department of Transportation. 2004. Keeping it Simple: Easy Ways to Help Wildlife Along Roads. Federal Highway Administration, Office of Natural Environment. 58p.
Van Wieren, S.P., ans P.B. Worm. 2001. The use of motorway wildlife overpass by large mammals. Netherlands Journal of Zoology 51(1): 97-105.