Roads and highways are, in an ecological sense, a set of bloody slashes across what were possibly some of the most vibrant ecosystems. They have been placed directly on top of wetlands, forests, and in certain cases, even run directly through mountains. The ecological effects of making a long line of uniform black asphalt through a natural community have severe effects on the biotic and abiotic aspects of the community.
One of the highly studied ways in which roads can impact the surrounding environment is through species fragmentation. By creating a bare surface on which there is no cover from the elements or predators, most microbiota have trouble traversing the road. Clearly, due to the lack of any substantial nutrients, no plants can survive on asphalt unless dirt accumulates in the cracks; this contributes to a whole set of other problems which I will discuss later. As a result of species fragmentation, different ecosystems can develop on either side of the road.
A common example of species fragmentation due to a natural event is the differentiation into different species of one type of squirrel due to the creation of one superhighway in New Jersey. Although species fragmentation is common in natural environments, it is often a factor that contributes to a species’ extinction in ecosystems that are already made fragile by other human disturbances (shopping malls, parking lots, industrial runoff).
Another commonly researched effect of roads is the runoff from the road. The creation of a road essentially creates a large flat area which is, for all practical purposes, unable to absorb water. As a result, the sediments, oils and chemicals from the asphalt, road paint, and tires runs off into the surrounding environment. The effects from there are highly varied. The most easily observable effect is a total dead zone for anywhere from 2 inches to 3 feet from the edge of the road. While this might not seem like a great area, when compounded over the many miles of roadside area and added to the road area itself, the dead zone is a significant detriment to local ecosystem biodiversity and richness.
A more slow-acting effect of road runoff is bioaccumulation of chemicals, specifically heavy metals. In the areas of the watershed that collect water from the roads, there is an observable difference in the amount of amphibians (usually frogs are identified), which are known to be indicator species. Though no studies have ever been done on the correlation between top level predator populations and road area, the raptor, wolf, and fox population drops severely with the presence of any road. This is due to a combination of: increase in offspring mortality with the presence of man-made chemicals and killing of the animals (usually foxes and wolves), as a result of road traffic and lack of prey.
From the combination of the increased water intake in combination with the increased and changed nutrient amounts, the vegetation next to the road (verge) also contrasts dramatically with the indigenous species of the area. This change in the primary producers of the ecosystem surrounding the road can create a totally new ecosystem with exotic plants and fauna brought from other areas via the outside of automobiles, and many times, the insides of eighteen wheelers, which often only open their cargo after a few hundred miles of travel.
Possibly the most unstudied and unappreciated effect of roads is the effect that the cars themselves have on the ecosystem. Ignoring the occasional car crash, oil leak, or spare tire on the side of the road, we take a look at the effects of normal car use on roadside ecosystems. First is the effect on native plant species. Plants require a certain period of uninterrupted dark in order to undergo natural flowering processes. When cars pass by at night with their headlights on, the plants are unable to flower properly, preventing propagation of the plant, even for the year after the road is built. The absence of the primary producers of an ecosystem causes the native fauna of the area to leave the area as well.
A further effect contributing to the loss of native fauna from the area is the noise pollution. The sound generated by even the best designed quiet automobiles is enough to scare away most animals, small and large. Only insects that can thrive on the verge are found in close to normal concentrations around the area of the road.
Roads are the infrastructure of almost every nation in the world. Although ships and planes have had glorious inventions and exciting histories, the automobile is what has consistently allowed nations to be unified not only through communication but through economy and industry. The fact is that roads probably will not change at all in the foreseeable future; the US alone is estimated to have enough roads to cover a state the size of South Carolina. What we need to do is to take into consideration the environmental impact of large scale changes we make in the future and to work to minimize the impact through our technology and knowledge of nature.
1. Forman, Richard T.T. and Alexander, Lauren E. “Roads and Their Major Ecological Effects” [accessed April 23, 2006] <http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.ecolsys.29.1.207;jsessionid=oF6JpZ3SQ6e8QskChR>
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