Roads are a prominent feature across landscapes, creating a disruption in continuous habitat that directly affects animal and plant populations. The road system in the United States affects 15-20% of the land (1). The “road effect zone” includes the area stripped and paved for highways as well as habitat adjacent to the roads. Some effects of roads include: increased pollution (heavy metals, salt, ozone, garbage), noise, and light (especially at night) (1, 2), easy routes for pest/invasive species dispersal (2, 3), spread of disease (4, 5), increased mortality due to road construction and wildlife-vehicle collisions (1, 2, 6, 7), decrease in species richness adjacent to roads (1, 8), and animal behavior changes including road avoidance (1, 2). Even national parks have roads that are impacting populations (9).
Roads have been documented as being a barrier to movement in a wide range of animal species, some of which include black bears (10), grizzly bears (11), badgers (12), elk (13), bumblebees (14), and small mammals (15). The width of the road may deter movement, as has been observed in rodents who cross narrow roads more often than wide ones (15). However, small roads, less than 3 meters wide, are still substantial barriers for prairie voles and cotton rats (16). Decreased movement across roads has also been attributed to the distance between habitats on either side of the road. Mice cross roads less frequently when the distance to the forest on either side of the road is greater (6). This is not true for all species though, even forest roads not open to the public are barriers to movement for mice and beetles (17).
The issue of reduced migration between populations is not only important for allowing individuals to expand the area they scavenge for resources, but also to maintain a genetically diverse population. Roads are creating genetic divergence among population of species ranging in size and vagility from bobcats and coyotes (18), deer (19), and bighorn sheep (20), to voles (21), salamanders (22), beetles (23), and frogs (24, 25). With limited genetic diversity populations can experience severe issues due to inbreeding eventually destroying the population. The death of one population will affect the health of all the populations that interact with it. This includes the other populations of the same species, but also other species that depend on it for food.
So what can we do to help alleviate the effects of roads? Use bikes, walk, or take public transportation when possible to reduce the number of vehicles on roads and the pollutants along them. Plant native vegetation around your house to increase resources for animals. Avoid destroying more habitat during construction projects. In general, be conscious of your impact on the environment, and if you feel there are improvements that can be made to local programs to help the environment speak up.
What impacts have you observed that roads have on the environment? Other ideas on how to alleviate those impacts?
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