Copyright © National Academy of Sciences. All rights reserved.
This executive summary plus thousands more available at http://www.nap.edu
Assessing and Managing the Ecological Impacts of Paved Roads
http://books.nap.edu/catalog/11535.html
6
Assessing and Managing the Impacts of Paved Roads
cause a shift in plant community structure when salt-sensitive plant species are replaced by less-sensitive species, such as cattails and common
reed grass. Salt-related vegetation changes can also affect wildlife by
adversely altering habitat, inhibiting road crossing by amphibian species,
and causing behavioral and toxicological impacts on birds and mammals.
Similarly, air pollution from vehicle exhaust (volatile organic compounds, nitrogen oxides, carbon monoxide, and particulate matter) can
alter the composition of roadside vegetation, promoting a few dominant
plant species at the expense of more sensitive species, such as ferns,
mosses, and lichens. This effect can extend up to 200 m from multilane
highways and up to 35 m from two-lane highways.
The underlying topography, aspect (the direction a site faces or its
exposure), geology, soils, ecological conditions, and land cover all influence how a road affects the environment. For example, the environmental effects of a road that does not cross a river are different from the
effects of one that crosses a river several times in a few kilometers. New
patterns of water runoff can develop as the local topography is altered.
Aspect can influence how quickly snow and ice melt off the road and
adjacent surfaces. Original topography, geology, and soils often dictate
the road path and provide construction constraints or opportunities. The
environmental effects of a road also depend on the prevailing land cover
and use, such as wildlands, wetlands, agricultural lands, or a river valley
versus a ridge. In fire-prone landscapes, a road can serve as a firebreak if
the road is wide enough or as a source of fire initiation if access to the
surrounding environment is increased.
Ecological productivity is influenced by roads. The roadside between the paved road and prevailing land cover often has lower productivity and different composition than the surrounding landscape (especially for roads through forests). The native habitat conditions of a roadside are frequently altered, but when the surrounding landscape is greatly
altered by development, roadsides can include some of the last remaining
habitats, especially for certain native plant species and some insects,
birds, and small mammals. Roadside areas can also facilitate the establishment of nonnative plants transported by vehicles, among other
mechanisms, including the clearing of land during road construction.
Biodiversity along roads typically is different from that in the surrounding landscape. Plants along roads must survive vehicular pollution, exposure to bright sunlight, dry soils, and regular mowing. Roadside plantings in the United States once consisted of grasses and herbs (often of
European origin) known to thrive in stressful conditions. Now there is
This executive summary plus thousands more available at http://www.nap.edu
Assessing and Managing the Ecological Impacts of Paved Roads
http://books.nap.edu/catalog/11535.html
6
Assessing and Managing the Impacts of Paved Roads
cause a shift in plant community structure when salt-sensitive plant species are replaced by less-sensitive species, such as cattails and common
reed grass. Salt-related vegetation changes can also affect wildlife by
adversely altering habitat, inhibiting road crossing by amphibian species,
and causing behavioral and toxicological impacts on birds and mammals.
Similarly, air pollution from vehicle exhaust (volatile organic compounds, nitrogen oxides, carbon monoxide, and particulate matter) can
alter the composition of roadside vegetation, promoting a few dominant
plant species at the expense of more sensitive species, such as ferns,
mosses, and lichens. This effect can extend up to 200 m from multilane
highways and up to 35 m from two-lane highways.
The underlying topography, aspect (the direction a site faces or its
exposure), geology, soils, ecological conditions, and land cover all influence how a road affects the environment. For example, the environmental effects of a road that does not cross a river are different from the
effects of one that crosses a river several times in a few kilometers. New
patterns of water runoff can develop as the local topography is altered.
Aspect can influence how quickly snow and ice melt off the road and
adjacent surfaces. Original topography, geology, and soils often dictate
the road path and provide construction constraints or opportunities. The
environmental effects of a road also depend on the prevailing land cover
and use, such as wildlands, wetlands, agricultural lands, or a river valley
versus a ridge. In fire-prone landscapes, a road can serve as a firebreak if
the road is wide enough or as a source of fire initiation if access to the
surrounding environment is increased.
Ecological productivity is influenced by roads. The roadside between the paved road and prevailing land cover often has lower productivity and different composition than the surrounding landscape (especially for roads through forests). The native habitat conditions of a roadside are frequently altered, but when the surrounding landscape is greatly
altered by development, roadsides can include some of the last remaining
habitats, especially for certain native plant species and some insects,
birds, and small mammals. Roadside areas can also facilitate the establishment of nonnative plants transported by vehicles, among other
mechanisms, including the clearing of land during road construction.
Biodiversity along roads typically is different from that in the surrounding landscape. Plants along roads must survive vehicular pollution, exposure to bright sunlight, dry soils, and regular mowing. Roadside plantings in the United States once consisted of grasses and herbs (often of
European origin) known to thrive in stressful conditions. Now there is