In today’s society, one may be hard-pressed to travel any distance without the aid of a road or specifically, “any strip of land, smoothed, paved, or otherwise prepared to allow easy travel” (wikipedia). This is not surprising since road construction is normally the first process in developing any new, uninhabited area. Dating as back as the Neolithic period, early humans inadvertently created roads by treading over the same path until the vegetation on that path deteriorated, thereby forming a trail. And as technology progressed, exploration, colonization, and trade between nations promoted the deliberate construction of roads. It is important to recognize the use of water transport as a favored means of transportation during the period of early European expansion; and then, the invention of the steam engine and railway system during the 1800s which sparked an automobile-dominant society. However, as roads remain the most commonly used method for travel, and seem to blend into the landscape nowadays, these roads negatively impact the ecosystem and humans alike. Road construction alters the physical and chemical environment, killing organisms in the process; but more importantly, such construction permanents affects and alters animal behavior and habitat.
For example, road construction directly leads to the increased mortality of slow-moving organisms, mostly flora. This is an obvious effect considering the estimated 13,107,812 km. of roads across the US with an average width of 3.65 m. per lane (not including shoulders or any extra clearing). Assuming that all the roads in the US average two lanes, and based on the previously stated width of the average lane, a reasonable and estimated land area covered by roads amounts to approximately 100,000 square km. Since the entire land area of the US is approximately 900,000 square km. (CIA Factbook), roads ultimately cover an astounding 1.1% of the Nation. The effect of performing such a large scale construction over the US is devastating and far-reaching. Simply building one road obliterates all life along its path, also injuring organisms under and adjacent to the road. Road construction compacts soil to an extent unsuitable for underground organisms to survive the initial paving of the road. In addition, organisms outside the immediate vicinity of the road suffer injuries during construction - for example, trees up to 30 m. from the road exhibit physical damage as a direct result of construction (Trombulak, 19).
Aside from the consequences resulting from the construction of a road, the final pavement itself causes many long-term effects on the environment. Roads generate and disperse substantial chemical and physical pollutants into the ecosystem, including noise, lighting, sand and other particles, heavy metals, and gases. First, noise produced by car traffic has been proven to reduce bird populations, possibly due to the inability of birds to hear mating calls over the noise pollution (Spellerberg). Second, light fixtures along roads alter the growth patterns of plants and behavior of animals. From previous Biology classes I learned that artificial light interrupts a plant’s natural night and day cycle, thereby wreaking havoc on the plant’s natural pollination. Basically, some plants exhibit photoperiodism, whereby short-day plants only bloom when exposed to short periods of light and long-day plants only bloom with long periods of light. Artificial lighting consequently tricks a plant into blooming by altering its exposure to light, causing an unnatural disruption in pollination. Third, sediment and other materials eroded from the roads sometimes transfer into nearby streams and bodies of water killing aquatic life forms. Vehicles using the roads and the roads themselves also add unnatural elements to the surrounding soil. The local flora absorb these heavy metals byproducts can be causing harm to the environment through a process called biomagnification, where the concentration of toxic substances increases in each successive link in the food chain. The final pollutant resulting from roads is toxic gas, mostly carbon dioxide and gaseous hydrocarbons. These chemicals have been noted to stunt growth of some plant species and increase growth of others, causing an imbalance in the natural proportions of species (Spellerberg, 320-321).
Along with its polluting effects, roads also impact animal behavior and the environment through habitat fragmentation. Habitat fragmentation is simply the breaking of large areas of habitat into smaller pieces. The following picture depicts the extent of fragmentation from only one road.
When a road interrupts an animal’s habitat, it does not present an absolute barrier to movement. However, the extent of the problem depends on a number of factors such as the size and traffic volume of the road. Ultimately, habitat fragmentation affects the size of habitats, leading to a distinct reduction the number of species in a certain area on or near the road. First to disappear are species that favor interior habitats, such as deep wooded areas. Another group of species immediately affected are those requiring more than one habitat as roads prevent them from reaching a specific land type necessary for their continued development. While it is possible that species favoring edge habitats might increase, studies show that the overall number of species still falls (The Nature Conservancy).
Roads also affect and are affected by humans whose actions in turn alter the environment. Roads increase ease and efficiency of transportation to remote areas resulting in changes to three human behaviors: hunting and fishing, recreation, and usage of land and water. Roads open up new areas for poaching and legal hunting and fishing. Unfortunately, once humans begin hunting in an originally undisturbed environment, they inevitably add more stress to the area. For example, fishing in previously inaccessible areas may lead to a higher demand for the native fish, resulting in more fishing. It is possible and likely that the increased fishing becomes unsustainable, leading to fish stocking in an attempt to artificially replenish fish populations. Unfortunately, stocked fish also alters the aquatic ecosystem permanently by competing with existing fishes for food and habitat, introducing diseases, feeding on the eggs of or adults fishes, and interbreeding with native fishes. In addition, it is nearly impossible to eradicate stocked fishes as they migrate to other bodies of water causing more unintended consequences. Another consideration is while roads increase man’s accessibility to newfound areas of the US, increasing the amount of tourism and recreational activities, it provides an opportunity to harass the native animals and plant species. Finally, roads are usually built to promote the development of land for residential, commercial, or industrial purposes, and with any human establishment, this development negatively affects the surrounding ecosystem (Trombulak, 24-25).
One could consider roads as a paved stretch of land that simply blends into the environment. However, they have unforeseen consequences of much greater importance than an unfortunate increase in road kill. Even though roads only account for a small percentage of the US land mass, their ecological effects are extensive. There is a necessity for careful road design and management in order to limit fragmentation of the habitat and reduce the dispersal of unnatural elements into the environment.
Spellerberg, Ian F. Sept. 1998. Ecological Effects of Roads and Traffic: A Literature Review. Global Ecology and Biogeography Letters. 7: 317-333.
Trombulak, Stephen C.; Frissell, Christopher A. Feb, 2000. Review of Ecological Effects of Roads on Terrestrial and Aquatic Communities. Conservation Biology. 14: 18-30.
Fish Stocking. North Carolina Wildlife Resources Commission. July 2005.<http://www.wildlife.state.nc.us/pg03_Fishing/pg3b6.htm>
United States. The World Factbook. Jan. 2006. <http://www.cia.gov/cia/publications/factbook/geos/us.html>
Fragmentation and Destruction of Habitat. The Nature Conservancy. May. 2002. <http://www.lastgreatplaces.org/berkshire/issues/art6588.html>
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