Assessing and Managing the Ecological Impacts of Paved Roads (2005) / Chapter Skim
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3 Effects of Roads on Ecological Condiditons
3 Effects of Roads on Ecological Condiditons
Pages 62-97
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From page 62... ...
Roads have effects that can vary with a range of spatial scales. The committee's analysis examines what is known about road effects at three scales, which are discussed later in the chapter.
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From page 63... ...
This chapter is organized into five sections to summarize the interaction between roads and ecological conditions. After this introduction, terms and concepts are defined in the second section.
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From page 64... ...
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From page 65... ...
. An enumeration of road effects on ecosystem goods and services is marginally addressed in this report.
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From page 66... ...
of road effects on ecological conditions, with an emphasis on spatial scale. The review included only studies that directly measured the effects of roads on the surrounding environment.
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From page 67... ...
The literature review and synthesis provides an overview of the current understanding, trends, and information gaps relating to the effects of roads and traffic on ecological conditions and the spatial scales at which roads affect ecological conditions. The available information at different scales of ecological effects is also examined.
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From page 68... ...
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From page 69... ...
69 e a ne ne ne ne None Few Few Non Few Few No Few No No No None s.at rmofebl ccessiayl rale rale ral rale ral ne Few Few Few Sev Few Sev Seve Sev Seve Few No Few readini not buteblalaiva on ati ral rale y rale ral rale ral y ral ral nya rmofni Seve Sev Man Sev Seve Sev Seve Man M Few Seve Seve reom ve noiat alityuq r ni jacentda pul poefildli ure ng itatbahlan reir itat ss rrido bar plants ands on hab co n tion chneri de n ental ng isticsr ructst onii itio edcu nte ersal ure roadsi W nctuF vemo Add Red Disp M Distribu itiosopmoC es rtalityom haotthguohtse ecipS adoR ndscapesla Nonnative ruct atintemgarF onii St nctuF sntatulloP itiosopmoC vironmnE aractehc Ecosystem gorietaC a
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From page 70... ...
. Reduced construction of new roads reduces habitat fragmentation, suggesting that, in general, less habitat fragmentation occurs in a less-dense road network with high traffic volumes than in a dense network with low traffic volumes per road mile.
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From page 71... ...
2001) concluded that most materials, including asphalt concrete and hydraulic cement concrete, used in the construction and repair of highways "behave in a benign fashion in the environment.
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From page 72... ...
in fluvial dynamics, sediment production, and chemical balances, which can adversely affect floodplain functioning and alter ecological conditions in aquatic and riparian areas (Figure 3-1)
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From page 73... ...
The nature of geomorphological processes affected by roads is strongly influenced by where and how roads are constructed, by the geology of the area, and by storm characteristics. Chemical Characteristics Water Quality The most observable abiotic environmental consequence of roads is the contribution of motor vehicles on paved roads to water pollution.
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From page 74... ...
In spite of the low contribution of constituents originating from the vehicle itself, vehicular traffic volume was identified as the principal factor influencing pollutant mass in highway runoff. That might be because vehicles are a transport mechanism as well as a source of pollution (Asplund et al.
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From page 75... ...
. There also is a strong correlation between concentrations of heavy metals and volatile matter in highway runoff (Flores-Rodriguez et al.
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From page 76... ...
For example, roads in mountainous areas can create landslides due to unstable soil and steep slopes. Paved road surfaces can increase water discharge rates in watersheds, thus increasing the potential for landslides and flash floods in streams and rivers.
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From page 77... ...
Below, the various categories of effects are discussed. The biotic consequences of the following effects of roads are considered below: direct effects include roads as barriers, enhancement of dispersal, roadkill, and effects on habitats; indirect effects include results of the access that roads provide to previously inaccessible areas, changes in water and air quality, and effects of lighting and noise.
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From page 78... ...
Roads as Barriers Roads can impede animal movements by direct mortality or avoidance behavior. The barrier effect varies between species, road types, and adjacent habitat quality; however, traffic volume and speed strongly influence the effect.
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From page 79... ...
The effects of roads on hydrological processes, most commonly through interfering with patterns of flow, have been the focus of many studies. Changes in hydrological processes affect ecosystem processes, such as habitat connectivity, primary productivity, decomposition, nutrient cycling, and disturbance regimes (for example, flooding frequency and intensity)
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From page 80... ...
80 Assessing and Managing the Ecological Impacts of Paved Roads BOX 3-1 Aquatic Culvert Design Effects Salmon have evolved to negotiate waterfalls during both up stream spawning migrations and downstream juvenile passage to the sea. However, this ability is fairly rare among fishes.
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From page 81... ...
Invasion of nonnative plants can also occur from vehicles transporting nonnative seeds into natural areas and clearing land during road construction (Tyser and Worley 1992, Parendes and Jones 2000, Gelbard and Belnap 2003)
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From page 82... ...
. Because paved roads (and to a lesser degree, unpaved roads)
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From page 83... ...
Depending on the nature of roadside verges, they can support abundant populations of some small mammals, insects, and birds, as well as native plant species. Roadside verges can also be important habitats for rare native plant species when juxtaposed in human-modified landscapes.
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From page 84... ...
. The construction of the James Dalton Highway from Fairbanks to Prudhoe Bay on Alaska's North Slope to service the Trans-Alaska Pipeline and provide road access to the large oil fields also has provided access to the North Slope for recreational hunters, anglers, and tourists, increasing the mortality of some animal species (NRC 2003)
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From page 85... ...
Salt runoff can damage vegetation, resulting in reductions in seeding establishment and flowering and fruiting of sensitive plant species; foliar, shoot, and root injury; and growth reductions. Areas affected by salt runoff also demonstrate a shift in plant community structure when salt-sensitive plant species are replaced by halophytic species, such as cattails and common reed grass (Environment Canada 2003)
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enriches roadside soil and changes plant composition, favoring a few dominant flowering plants at the expense of more sensitive plant species (for example, ferns, mosses, and lichens)
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From page 87... ...
. For example, wetland species diversity is negatively correlated with paved-road density up to 2 km from wetlands (Findlay and Houlahan 1997)
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From page 88... ...
americanus) 1990 Increase in edge species Component of bird community 100 m Ferris 1979 Road density Wetlands species richness 2,000 m Findlay and Houlahan Moor frog (Rana arvalis)
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From page 89... ...
Thus, a synthesis of available information or metaanalysis could provide valuable insight into the extent of effects at a broader scale than is known today. The committee found that very little research covers long periods, and almost no research has addressed large spatial scales of road effects.
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From page 90... ...
However, the impact of chemical pollutants, both organics and heavy metals, can be long lived (such as contaminated drinking-water sources) and far reaching (such as atmospheric deposition)
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Department of Defense.) The figure suggests that ecological effects of roads can alter ecological processes over scales that range from minutes to centuries (time)
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The nature of ecological interactions at various scales has been the subject of much scientific debate. The focus has been on the interaction between processes and their associated structures that operate for long periods and over large spatial scales and processes that are faster and smaller.
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From page 93... ...
or community composition, occur primarily within this zone or within an area of a few hundred meters perpendicular to the road segment. Some road effects cross scales of space and time.
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From page 94... ...
Cumulative Effects Even though the awareness of the ecological effects of roads has grown steadily over the past few decades, only a small body of literature addresses cumulative effects associated with roads. In evaluating effects of oil and gas activity on Alaska's North Slope, the NRC (2003)
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From page 95... ...
In some cases, the roads are built to support the new activities and, in other cases, the roads lead to the additional development. INFORMATION GAPS Historically, most studies of road effects have been carried out at the project level, with local studies focusing on specific transportation effects.
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Future studies on the ecological impacts of roads should be published in the peer-reviewed venues. SUMMARY Roads influence ecological conditions across a range of organizational levels and scales.
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From page 97... ...
More research should be directed at identifying the appropriate scale at which roads affect ecological conditions. Information on the resiliency of biodiversity components to roadrelated disturbances is needed to better understand the effects of roads on ecological systems.
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