Paving Paradise: The Ecological Effects of Road Improvement
As the human population grows, our wildlands face threats from increased access for recreation and resource extraction, subdivision for residential and commercial development, and movements to pave and improve many of our secondary and tertiary roads. Road improvements include paving, widening, and/or other methods. While paving may afford conveniences that satisfy commercial and residential demands, such improvements increase the detrimental ecological impacts of roads including direct effects such as fragmentation and loss of secure wildlife habitat (Forman & Alexander, 1998), increased vehicle-wildlife collisions (Trombulak & Frissell, 2000), construction-related wildlife mortality (Trombulak & Frissell, 2000), changes in groundwater flow and stream morphology (Malecki, 2005), spread of wildfire (Pew & Larsen, 2001) and invasive species (Gelbard & Belnap, 2003; Trombulak & Frissell, 2000), and increased chemical pollutants that leach into our watersheds and harm flora and fauna (National Research Council, 2005; Tromulak & Frissell, 2000; Forman & Alexander, 1998).
Increased human access due to road improvements intensifies all of the above problems, leading to degradation of ecosystems and loss of biodiversity (Ledec & Posas, 2003). Human contact with wildlife is also increased, posing threats to both wildlife and human safety (Herrero et al., 2005; Benn and Herrero, 2002; Herrero, 2002). In this article, I review how road paving and improvements can lead to increased ecological impacts.
Vehicle-wildlife collisions
Vehicle collisions with wildlife present danger for both humans and wildlife, and economic losses in the form of vehicle damage, health care for human injuries, and loss of revenue attached to hunting of game species (Schwabe & Schuhmann, 2002; Langley et al., 2006; Gordon et al., 2004). By the end of the 20th century, vehicle collisions with wildlife replaced hunting as the leading direct cause of mortality in terrestrial vertebrates (Forman & Alexander, 1998).
Leblond et al. (2007) identify road improvement as a major contributing factor to the growing rate of vehicle-wildlife collisions. As early as the 1970s, it was found that small mammals had higher mortality with increased traffic and speeds (Oxley et al., 1974). Studies in Brazil found higher rates of roadkill following road paving (Coehlo et al., 2005; Bueno et al. 2005). Also, an upgraded road in Australia resulted in a dramatic increase in the number of road-killed Tasmanian devils and eastern quolls (Jones, 2000).
The barrier effect: road avoidance and habitat fragmentation
Despite the wide-ranging effects of roads on a landscape level, most transportation engineers consider only the ecological effects on the land occupied by the road itself and the narrow verge immediately flanking it (Forman, 2000). Forman and Alexander (1998) report that road width and traffic density determine the intensity of the “barrier effect” that results in avoidance of roads by wildlife, leading to habitat fragmentation and dividing existing populations into smaller, isolated metapopulations. Metapopulations are more susceptible to stochastic extinction due to genetic isolation and increased pressure on resources, while habitat fragmentation impedes recolonization (Noss et al., 1996; Forman and Alexander, 1998).
Elk (Cervus elaphus), moose (Alces alces), grizzly bear (Ursus arctos), gray wolves (Canis lupus), mountain lions (Puma concolor), Canada lynx (Lynx canadensis), American marten (Martes americana), wolverines (Gulo gulo), and other mustelids are all known to avoid roads (e.g., Ward, 1976; Frederick, 1991; Dickson et al., 2005; Dussault et al., 2007), especially those with higher speeds and volumes, making them highly susceptible to the barrier effect. Carnivores are especially sensitive to roads and human development, presenting wider implications for the ecosystem because top carnivores can regulate populations of prey species that may become overpopulated in their absence (Weaver, 2001).
Spread of invasive species
Roads facilitate the spread of invasive and exotic species through seeds carried along vehicles and the air turbulence caused by passing vehicles, both problems that increase as greater numbers of vehicles travel on roads once they are improved (Trombulak & Frissell, 2000; Forman & Alexander, 1998; Gelbard & Belnap, 2003). Road improvements increase the degree of clearance and allow more penetration of sunlight, increasing the edge effect of existing roads (Noss, 1995). The area covered by invasive plant species such as knapweed tends to be wider along paved roads than unimproved roads (Gelbard & Belnap, 2003).
Wildfire
Human access often increases the levels of accidental and intentional ignition of wildfires (Brosofske & Cleland, 2007). Pew and Larsen (2001) found that the occurrence of human-caused wildfire was highest along roads and railroads, but that the rate of ignition dropped off with distance from human infrastructure, and dramatically more with distance from unimproved roads than from paved roads.
Chemical pollutants
Paved roads leach chemical pollutants both from the paving materials and from deposition of exhaust and tire rubber from the vehicles that travel them (Forman & Alexander, 1998; National Research Council, 2005). Asphalt roads leach carcinogenic polycyclic aromatic hydrocarbons (PAH’s) from both car exhaust deposition and asphalt that are harmful to highway workers as well as flora and fauna and leach into the watershed (Sadler et al. 1997). Nitrogen oxide and ozone from vehicle exhaust damage plant life and pollute the atmosphere (Forman & Hersperger, 1996).
Conclusion
Road improvements exacerbate the negative ecological effects of the existing road system by increasing access, traffic speed and volume, and contributing to higher levels of pollutants produced by paving materials and vehicle traffic. Transportation-related mortality, road avoidance, and airborne dust can be reduced with lower speed limits, and unimproved roads can be maintained safely and effectively by adding gravel when needed and possibly through dust abatement strategies, although dust coating can damage plant life, attract wildlife to roads, and leach into groundwater (Missouri Department of Natural Resources, 2006; Lux, 2002).
Shannon Donahue is a University of Montana Environmental Studies graduate student.
References
Benn, B. and S. Herrero. 2002. Grizzly bear mortality and human access in Banff and Yoho National Parks. Ursus 13: 213-221.
Brosofske, K.D., & D.T. Cleland. 2007. Factors influencing modern widlfire occurrence in the Mark Twain National Forest, Missouri. Southern Journal of Applied Forestry 31(2): 73-84.
Bueno, A., S.C.S. Belentani, and M.C. Ribeiro. 2005. Wildlife road mortality in Triângulo Mineiro, southeastern Brazil. Proceedings of the 19th Annual Meeting of the Society for Conservation Biology, July 15-19, Brasilia, Federal District, Brazil.
Coelho, I.P, A. Kindel, and A. Coelho. 2005. Vertebrate road-kills in two highways crossing the Mata Atlantica Biosphere Reserve in southern Brazil. Proceedings of the 19th Annual Meeting of the Society for Conservation Biology, July 15-19, Brasilia, Federal District, Brazil.
Dickson, B.G., J.S. Jenness & P. Beir. 2005. Influence of vegetation, topography, and roads on cougar movement in Southern California. Journal of Wildlife Management 69(1): 264-276.
Dussault, C., J. Ouellet, C. Laurian, R. Courtois, & L. Breton. 2007. Moose movement rates along highways and crossing probability models. Journal of Wildlife Management 71(7): 2338-2345.
Forman, R.T. 2000. Estimate of the area affected ecologically by the road system in the United States. Conservation Biology 14(1): 31-35.
Forman, R.T., & H.A. Hersperger. 1996. Road ecology and road density in different landcapes, with international planning and mitigation solutions. In: Transportation and wildlife: reducing wildlife mortality and improving wildlife passageways across transportation corridors. Gary Evink et al. (Ed.), Proceedings from the Transportation Related Wildlife Mortality Seminar. Federal Highway Administration, FL-ER 58-96. pp 1-23.
Forman, R.T., & L.E. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematics 29: 207-231+C2.
Frederick, G.P. 1991. Effects of forest roads on grizzly bears, elk, and gray wolves: A literature review. USDA Forest Service, Kootenai National Forest, Montana. 49 pp.
Gelbard, J., & J. Belnap. 2003. Roads as conduits for exotic plant invations in a semiarid landscape. Conservation Biology 17(2): 420-432.
Gordon, K.M., M.C. McKinstry, & S.H. Anderson. 2004. Motorist response to a deer-sensing warning system. Wildlife Society Bulletin 32(2): 565-573.
Herrero, S. 2002. Bear Attacks: their causes and avoidance, revised edition. Guilford, CT: The Lyons Press.
Herrero, S., T. Smith, T.D. DeBruyn, K. Gunther, & C. Matt. 2005. From the Field: Brown Bear Habituation to People--Safety, Risks, and Benefits. Wildlife Society Bulletin 33(1): 362-373.
Langley, R.L., S.A. Higgins, & K.B. Herrin. 2006. Risk factors associated with fatal animal-vehicle collisions in the United States, 1995-2004. Wilderness and Environmental Medicine 17(4): 229-239.
Leblond, M., C. Dussault, J. Ouellet, M. Poulin, R. Courtois, & al., e. 2007. Electric fencing as a measure to reduce moose-vehicle collisions. Journal of Wildlife Management 71(5): 1695-1703.
Ledec, G., & P. Posas. 2003. Biodiversity conservation in road projects: Lessons from World Bank experience in Latin America. 8th International Conference on Low-Volume Roads. Reno, NV, USA.
Lux, C. 2002. The North Fork Road: Possible maintenance alternatives and landowner opinions. Retrieved March 14, 2008, from http://www.gravel.org/articles/LuxReport.pdf
Malecki, R.W. 2006. A New Way to Look at Forest Roads: the Road Hydrologic Impact Rating System (RHIR). Road-RIPorter 11(3): 12-13.
Missouri Department of Natural Resources. 2006. Dust suppression on unpaved roads. Retrieved February 4, 2008, from http://www.dnr.mo.gov/env/apcp
National Research Council. 2005. Assessing and managing the ecological impacts of paved roads. Washington, D.C.: The National Academy Press.
Noss, R. F. 1995. The ecological effects of roads or The road to destruction. Unpublished report. Wildlands CPR.
Noss, R.F., H.B. Quigley, M. Honrocker, T. Merrill, & P.C. Paquet. 1996. Conservation biology and carnivore conservation in the Rocky Mountains. Conservation Biology 10: 949-963.
Oxley, D.J., M.B. Fenton, and G.R. Carmody. 1974. The ecological effects of roads on populations of small mammals. Journal of Applied Ecology 11: 51-59.
Pew, K., & C. Larsen. 2001. GIS analysis of spatial and temporal patterns of human-caused wildfires in the temperate rain forest of Vancouver Island, Canada. Forest Ecology and Management 140: 1-18.
Sadler, Ross and C. Delamont, P. White and D. Connell. 1997. Contaminants in soil as a result of leaching from asphalt. Toxicological and Environmental Chemistry, 68: 71-81.
Schwabe, K.A., & P.W. Schuhmann. 2002. Deer-vehicle collisions and deer value: an analysis of competing literatures. Wildlife Society Bulletin 30: 609-615.
Trombulak, S., & C. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology 14: 18-30.
Ward, A.L. 1976. Elk behavior in relation to timber harvest operations and traffic on the Medicine Bow Range in south-central Wyoming. Proceedings of the Elk-Logging-Roads Symposium, 16-17 December 1975 (pp. 32-43). Moscow, Idaho, USA: Forest, Wildlife and Range Experiment Station, University of Idaho.
Weaver, J.L. 2001. The Transboundary Flathead: A critical landscape for carnivores in the Rocky Mountains. WCS Working Papers No. 18, July 2001 .
Increased human access due to road improvements intensifies all of the above problems, leading to degradation of ecosystems and loss of biodiversity (Ledec & Posas, 2003). Human contact with wildlife is also increased, posing threats to both wildlife and human safety (Herrero et al., 2005; Benn and Herrero, 2002; Herrero, 2002). In this article, I review how road paving and improvements can lead to increased ecological impacts.
Vehicle-wildlife collisions
Vehicle collisions with wildlife present danger for both humans and wildlife, and economic losses in the form of vehicle damage, health care for human injuries, and loss of revenue attached to hunting of game species (Schwabe & Schuhmann, 2002; Langley et al., 2006; Gordon et al., 2004). By the end of the 20th century, vehicle collisions with wildlife replaced hunting as the leading direct cause of mortality in terrestrial vertebrates (Forman & Alexander, 1998).
Leblond et al. (2007) identify road improvement as a major contributing factor to the growing rate of vehicle-wildlife collisions. As early as the 1970s, it was found that small mammals had higher mortality with increased traffic and speeds (Oxley et al., 1974). Studies in Brazil found higher rates of roadkill following road paving (Coehlo et al., 2005; Bueno et al. 2005). Also, an upgraded road in Australia resulted in a dramatic increase in the number of road-killed Tasmanian devils and eastern quolls (Jones, 2000).
The barrier effect: road avoidance and habitat fragmentation
Despite the wide-ranging effects of roads on a landscape level, most transportation engineers consider only the ecological effects on the land occupied by the road itself and the narrow verge immediately flanking it (Forman, 2000). Forman and Alexander (1998) report that road width and traffic density determine the intensity of the “barrier effect” that results in avoidance of roads by wildlife, leading to habitat fragmentation and dividing existing populations into smaller, isolated metapopulations. Metapopulations are more susceptible to stochastic extinction due to genetic isolation and increased pressure on resources, while habitat fragmentation impedes recolonization (Noss et al., 1996; Forman and Alexander, 1998).
Elk (Cervus elaphus), moose (Alces alces), grizzly bear (Ursus arctos), gray wolves (Canis lupus), mountain lions (Puma concolor), Canada lynx (Lynx canadensis), American marten (Martes americana), wolverines (Gulo gulo), and other mustelids are all known to avoid roads (e.g., Ward, 1976; Frederick, 1991; Dickson et al., 2005; Dussault et al., 2007), especially those with higher speeds and volumes, making them highly susceptible to the barrier effect. Carnivores are especially sensitive to roads and human development, presenting wider implications for the ecosystem because top carnivores can regulate populations of prey species that may become overpopulated in their absence (Weaver, 2001).
Spread of invasive species
Roads facilitate the spread of invasive and exotic species through seeds carried along vehicles and the air turbulence caused by passing vehicles, both problems that increase as greater numbers of vehicles travel on roads once they are improved (Trombulak & Frissell, 2000; Forman & Alexander, 1998; Gelbard & Belnap, 2003). Road improvements increase the degree of clearance and allow more penetration of sunlight, increasing the edge effect of existing roads (Noss, 1995). The area covered by invasive plant species such as knapweed tends to be wider along paved roads than unimproved roads (Gelbard & Belnap, 2003).
Wildfire
Human access often increases the levels of accidental and intentional ignition of wildfires (Brosofske & Cleland, 2007). Pew and Larsen (2001) found that the occurrence of human-caused wildfire was highest along roads and railroads, but that the rate of ignition dropped off with distance from human infrastructure, and dramatically more with distance from unimproved roads than from paved roads.
Chemical pollutants
Paved roads leach chemical pollutants both from the paving materials and from deposition of exhaust and tire rubber from the vehicles that travel them (Forman & Alexander, 1998; National Research Council, 2005). Asphalt roads leach carcinogenic polycyclic aromatic hydrocarbons (PAH’s) from both car exhaust deposition and asphalt that are harmful to highway workers as well as flora and fauna and leach into the watershed (Sadler et al. 1997). Nitrogen oxide and ozone from vehicle exhaust damage plant life and pollute the atmosphere (Forman & Hersperger, 1996).
Conclusion
Road improvements exacerbate the negative ecological effects of the existing road system by increasing access, traffic speed and volume, and contributing to higher levels of pollutants produced by paving materials and vehicle traffic. Transportation-related mortality, road avoidance, and airborne dust can be reduced with lower speed limits, and unimproved roads can be maintained safely and effectively by adding gravel when needed and possibly through dust abatement strategies, although dust coating can damage plant life, attract wildlife to roads, and leach into groundwater (Missouri Department of Natural Resources, 2006; Lux, 2002).
Shannon Donahue is a University of Montana Environmental Studies graduate student.
References
Benn, B. and S. Herrero. 2002. Grizzly bear mortality and human access in Banff and Yoho National Parks. Ursus 13: 213-221.
Brosofske, K.D., & D.T. Cleland. 2007. Factors influencing modern widlfire occurrence in the Mark Twain National Forest, Missouri. Southern Journal of Applied Forestry 31(2): 73-84.
Bueno, A., S.C.S. Belentani, and M.C. Ribeiro. 2005. Wildlife road mortality in Triângulo Mineiro, southeastern Brazil. Proceedings of the 19th Annual Meeting of the Society for Conservation Biology, July 15-19, Brasilia, Federal District, Brazil.
Coelho, I.P, A. Kindel, and A. Coelho. 2005. Vertebrate road-kills in two highways crossing the Mata Atlantica Biosphere Reserve in southern Brazil. Proceedings of the 19th Annual Meeting of the Society for Conservation Biology, July 15-19, Brasilia, Federal District, Brazil.
Dickson, B.G., J.S. Jenness & P. Beir. 2005. Influence of vegetation, topography, and roads on cougar movement in Southern California. Journal of Wildlife Management 69(1): 264-276.
Dussault, C., J. Ouellet, C. Laurian, R. Courtois, & L. Breton. 2007. Moose movement rates along highways and crossing probability models. Journal of Wildlife Management 71(7): 2338-2345.
Forman, R.T. 2000. Estimate of the area affected ecologically by the road system in the United States. Conservation Biology 14(1): 31-35.
Forman, R.T., & H.A. Hersperger. 1996. Road ecology and road density in different landcapes, with international planning and mitigation solutions. In: Transportation and wildlife: reducing wildlife mortality and improving wildlife passageways across transportation corridors. Gary Evink et al. (Ed.), Proceedings from the Transportation Related Wildlife Mortality Seminar. Federal Highway Administration, FL-ER 58-96. pp 1-23.
Forman, R.T., & L.E. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematics 29: 207-231+C2.
Frederick, G.P. 1991. Effects of forest roads on grizzly bears, elk, and gray wolves: A literature review. USDA Forest Service, Kootenai National Forest, Montana. 49 pp.
Gelbard, J., & J. Belnap. 2003. Roads as conduits for exotic plant invations in a semiarid landscape. Conservation Biology 17(2): 420-432.
Gordon, K.M., M.C. McKinstry, & S.H. Anderson. 2004. Motorist response to a deer-sensing warning system. Wildlife Society Bulletin 32(2): 565-573.
Herrero, S. 2002. Bear Attacks: their causes and avoidance, revised edition. Guilford, CT: The Lyons Press.
Herrero, S., T. Smith, T.D. DeBruyn, K. Gunther, & C. Matt. 2005. From the Field: Brown Bear Habituation to People--Safety, Risks, and Benefits. Wildlife Society Bulletin 33(1): 362-373.
Langley, R.L., S.A. Higgins, & K.B. Herrin. 2006. Risk factors associated with fatal animal-vehicle collisions in the United States, 1995-2004. Wilderness and Environmental Medicine 17(4): 229-239.
Leblond, M., C. Dussault, J. Ouellet, M. Poulin, R. Courtois, & al., e. 2007. Electric fencing as a measure to reduce moose-vehicle collisions. Journal of Wildlife Management 71(5): 1695-1703.
Ledec, G., & P. Posas. 2003. Biodiversity conservation in road projects: Lessons from World Bank experience in Latin America. 8th International Conference on Low-Volume Roads. Reno, NV, USA.
Lux, C. 2002. The North Fork Road: Possible maintenance alternatives and landowner opinions. Retrieved March 14, 2008, from http://www.gravel.org/articles/LuxReport.pdf
Malecki, R.W. 2006. A New Way to Look at Forest Roads: the Road Hydrologic Impact Rating System (RHIR). Road-RIPorter 11(3): 12-13.
Missouri Department of Natural Resources. 2006. Dust suppression on unpaved roads. Retrieved February 4, 2008, from http://www.dnr.mo.gov/env/apcp
National Research Council. 2005. Assessing and managing the ecological impacts of paved roads. Washington, D.C.: The National Academy Press.
Noss, R. F. 1995. The ecological effects of roads or The road to destruction. Unpublished report. Wildlands CPR.
Noss, R.F., H.B. Quigley, M. Honrocker, T. Merrill, & P.C. Paquet. 1996. Conservation biology and carnivore conservation in the Rocky Mountains. Conservation Biology 10: 949-963.
Oxley, D.J., M.B. Fenton, and G.R. Carmody. 1974. The ecological effects of roads on populations of small mammals. Journal of Applied Ecology 11: 51-59.
Pew, K., & C. Larsen. 2001. GIS analysis of spatial and temporal patterns of human-caused wildfires in the temperate rain forest of Vancouver Island, Canada. Forest Ecology and Management 140: 1-18.
Sadler, Ross and C. Delamont, P. White and D. Connell. 1997. Contaminants in soil as a result of leaching from asphalt. Toxicological and Environmental Chemistry, 68: 71-81.
Schwabe, K.A., & P.W. Schuhmann. 2002. Deer-vehicle collisions and deer value: an analysis of competing literatures. Wildlife Society Bulletin 30: 609-615.
Trombulak, S., & C. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Conservation Biology 14: 18-30.
Ward, A.L. 1976. Elk behavior in relation to timber harvest operations and traffic on the Medicine Bow Range in south-central Wyoming. Proceedings of the Elk-Logging-Roads Symposium, 16-17 December 1975 (pp. 32-43). Moscow, Idaho, USA: Forest, Wildlife and Range Experiment Station, University of Idaho.
Weaver, J.L. 2001. The Transboundary Flathead: A critical landscape for carnivores in the Rocky Mountains. WCS Working Papers No. 18, July 2001 .