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
Summary
5
the survival probability of local populations, including endangered or
threatened species, such as the Florida panther and grizzly bear. In addition to vehicle-related mortality, roads―acting as barriers to wildlife
movement—may affect wildlife-population structure by disrupting
breeding patterns or impairing reproductive success because they can
fragment and isolate populations. In extreme cases, the resulting limitation of gene flow could result in local extirpation of a species. Properly
designed mitigation measures, such as wildlife-crossing structures, can
facilitate wildlife movement across roads and reconnect isolated populations. Fish movement can also be blocked by road-crossing structures,
such as culverts (usually a large pipe under a road where it crosses a
stream) that are improperly designed or not present at all. Some fishes
avoid moving through culverts, possibly because of the increased speed
of the water flow, even if there are better habitat conditions on the opposite side. Reluctance to move, for example, downstream, could contribute to isolating upstream populations and, in some cases, localized extirpations.
In evaluating the ecological effects of roads, it is important to consider the physical, socioeconomic, and legal context, as well as the ecological context. Each has spatial and temporal dimensions. The term
“road-effect zone” means the distance from a stretch of road or road segment that ecological effects can be detected. The road-effect zone is
usually asymmetric extending outward on either side of the road, with
varying zone boundaries. The effect of distance varies, depending on the
species, location, and disturbance type. For example, animals avoid
roads by a distance that increases with increasing traffic volume, and that
distance varies by species. Noise from high-traffic-volume roads reduces
the breeding densities and distribution of many bird species within a 40to 1,500-m zone. Increased traffic and road density negatively affect
aquatic habitats and the species that depend on them. For example, wetland species diversity is negatively correlated with paved roads up to 2
km away. Other disturbances, such as heavy metals and chemical pollution, can degrade habitat quality in the road-effect zone up to 100 m and
200 m, respectively. Vehicle-generated pollutants (such as nitrogen oxides, petroleum, lead, copper, chromium, zinc, and nickel) are the primary pollutants associated with road use. Along with pollutants from
spills, litter, and adjacent land uses, they accumulate on impervious roads
and enter waterways via surface runoff or atmospheric deposition. Runoff contaminated with road salt can damage vegetation and potentially
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
Summary
5
the survival probability of local populations, including endangered or
threatened species, such as the Florida panther and grizzly bear. In addition to vehicle-related mortality, roads―acting as barriers to wildlife
movement—may affect wildlife-population structure by disrupting
breeding patterns or impairing reproductive success because they can
fragment and isolate populations. In extreme cases, the resulting limitation of gene flow could result in local extirpation of a species. Properly
designed mitigation measures, such as wildlife-crossing structures, can
facilitate wildlife movement across roads and reconnect isolated populations. Fish movement can also be blocked by road-crossing structures,
such as culverts (usually a large pipe under a road where it crosses a
stream) that are improperly designed or not present at all. Some fishes
avoid moving through culverts, possibly because of the increased speed
of the water flow, even if there are better habitat conditions on the opposite side. Reluctance to move, for example, downstream, could contribute to isolating upstream populations and, in some cases, localized extirpations.
In evaluating the ecological effects of roads, it is important to consider the physical, socioeconomic, and legal context, as well as the ecological context. Each has spatial and temporal dimensions. The term
“road-effect zone” means the distance from a stretch of road or road segment that ecological effects can be detected. The road-effect zone is
usually asymmetric extending outward on either side of the road, with
varying zone boundaries. The effect of distance varies, depending on the
species, location, and disturbance type. For example, animals avoid
roads by a distance that increases with increasing traffic volume, and that
distance varies by species. Noise from high-traffic-volume roads reduces
the breeding densities and distribution of many bird species within a 40to 1,500-m zone. Increased traffic and road density negatively affect
aquatic habitats and the species that depend on them. For example, wetland species diversity is negatively correlated with paved roads up to 2
km away. Other disturbances, such as heavy metals and chemical pollution, can degrade habitat quality in the road-effect zone up to 100 m and
200 m, respectively. Vehicle-generated pollutants (such as nitrogen oxides, petroleum, lead, copper, chromium, zinc, and nickel) are the primary pollutants associated with road use. Along with pollutants from
spills, litter, and adjacent land uses, they accumulate on impervious roads
and enter waterways via surface runoff or atmospheric deposition. Runoff contaminated with road salt can damage vegetation and potentially