Roads – Pathways for Humans, Barriers for Functioning Ecosystems
For decades, we have designed roads to improve their safety and efficiency; more recently, we have tried to mitigate the negative environmental impacts of road construction, such as erosion and sediment run-off at the site level. We are now beginning to understand that roads can have ongoing negative impacts on wild- life and the health of our ecosystems, and that the ecological footprint of a road is not restricted to the road corridor itself. This is especially important in Ontario where population growth is forcing the continual expansion of urban boundaries into natural areas and is putting development pressures on intact ecosystems.
The emerging science of road ecology explores and addresses the relationship between the natural environment and the road system. Roads have both direct and indirect impacts on wildlife and ecosystems, and the interactions can be both nuanced and profound. Habitat fragmentation, the creation of barriers to wildlife movement (and, therefore, the flow of genes between populations), high mortality rates through roadkill, the pollution and silting of streams, and the introduction of invasive species are just a few of the possible ecological impacts.
Effects of Roads on Wildlife
Being killed while crossing a road has an obvious negative effect on an individual member of a wildlife population, not to mention the dangers such a collision can pose to the people in the vehicle that strikes the animal and other vehicles in the vicinity. Ontario averages more than 10,000 wildlife-vehicle collisions a year or one every 38 minutes, mostly along undivided two-way roads. Road-related mortality can be particularly devastating to populations of species that have low reproductive rates (such as mammalian predators and turtles) and those that are wide-ranging or undertake seasonal migrations (for example, mammalian predators, snakes and amphibians). Ontario’s multi-turtle species at risk recovery team has identified road mortality as one of the main threats to turtle species at risk. In fact, studies in the United States have found that the ratio of male to female aquatic turtles has increased as road density has increased. This is due to the fact that female turtles are more susceptible to road mortality during their migration to nest locations. Populations cannot compensate for this loss of egg-bearing females. An Ontario study on roadkill of frogs and toads found that road mortality has a significant effect on local population densities. For some species, vehicle speed correlates with road mortality; for other species, it is the volume of traffic on the road that has more of an impact.
While many species avoid roads, reptiles and some insects are attracted to roads as a warm, open place to bask and because sandy road shoulders make attractive nesting sites, which increases the risk of being hit by vehicles. Similarly, red-winged blackbirds can be more abundant closer to roads because of the abundance of cattails in roadside ditches. Bridges provide roosting for bats, and some raptors and ravens benefit from additional perching sites in the form of hydro poles along the road corridor. All of these situations bring wildlife closer to roads where the risk of being struck by a vehicle is increased.
Wide-ranging carnivores, such as wolves and coyotes, are particularly susceptible to road mortality. When there are fewer top predators, it can result in the overgrazing and overpopulation of habitats by their former prey. There is a cascading effect through the ecosystem as these top predator populations are impacted by roads. The ECO provides more detail on mammalian predator management policies in Wildlife Management: Ontario’s Mammalian Predators
Mineral-deficient deer and moose come to roads for salt. Recent studies have found that the ingestion of road salt by wildlife can have a temporary, debilitating intoxication effect. Studies at Algonquin Provincial Park and at Mount Revelstoke National Park in British Columbia suggest that salt toxicity caused by the ingestion of sodium chloride impairs wildlife brain function. Impairment makes wildlife less able to avoid being struck by vehicles, and salt ingestion has been implicated in songbird losses. The ECO discussed the effects of road salt on aquatic and terrestrial ecosystems extensively in Road salt: Can ice-free roads and environmental protection be reconciled?
Road Avoidance and Habitat Fragmentation
While some species are attracted to roads, others avoid roads. Roads fragment suitable habitat for wildlife and isolate populations from one another causing a loss of gene flow between populations. This can result in small, isolated populations that are not self-sustaining because there are no new breeding adults entering the population. These populations may eventually disappear altogether. This ultimately results in a loss of biodiversity.
The species most vulnerable to the barrier effect of roads are those that travel over large areas and are the same species mentioned earlier (mammalian predators, reptiles and amphibians) that are particularly susceptible to road mortality. Species that share this trait are the large predators that act as keystone species: species that are long-lived, slow to reproduce, wide-ranging, require specialized habitat, and have been actively eradicated from much of their former range. Keystone species act as the backbone of an ecosystem; detrimental impacts to them ultimately impact the other species within that ecosystem, as well as how that ecosystem effectively functions. One study found that all wolf pack territories in the western Great Lakes area of the United States occurred on one side or the other of a major highway. The packs actually adjusted their territories so that they would not have to cross the highway. Similarly, bears shift their home ranges to areas of lower road densities. As reported in the ECO’s 2006-2007 Annual Report, much of the range recession of woodland caribou in Ontario is coincident with landscape- level fragmentation of habitat – and the subsequent isolation of caribou populations – caused by logging, land clearing, and road building. Studies in Boston have found that birds, such as bobolinks and eastern meadowlarks, don’t reproduce near roads.
A time lag occurs, sometimes stretching to decades, before the environmental effects of roads on wildlife populations can be fully observed. The loss of habitat is the most immediate effect. The effects of road-related wildlife mortality take longer. Where roadkill numbers are large, the effect should be observable after the road has been in place for approximately one or two generations of the animal species. The barrier effect that isolates populations and disrupts gene flow will take several further generations to become manifest.
Effects of Roads on the Landscape
The environmental effects of road systems are not always immediate, nor are they isolated to just the area occupied by the road itself. The impacts can be cumulative and far-reaching. Immediate effects, such as the direct loss of habitat, can sometimes be mitigated by habitat restoration. The unforeseen impacts, which may also have a time lag, are insidious and difficult to anticipate. The continuing fragmentation and isolation of patches of habitats will eventually reach the point where populations of associated species can no longer be sustained.
Effects on Streams
Chemicals and pollutants from vehicles, roads and bridges, and their effects on streams, have been well documented. Spills of oil, gasoline, industrial chemicals, objects discarded from vehicles, sand, salt, herbicides and the materials that come from degrading vehicle tires and road surfaces are all carried to and eventually deposited in streams. The hydrology of streams and wetlands change when they are channelized or redirected by culverts or ditches, and when small headwater tributaries are eliminated altogether. As roads are built, the amount of impervious (hard surface) area in a watershed increases. This leads to rapid, high volume run-off, carrying the sand, salt and other contaminants found on the roads into streams. All of this sedimentation, together with other hydrological changes, result in streams that are more likely to food in wet weather, to dry up under drought conditions, and to be otherwise degraded.
Roads provide pathways along which invasive, non-native plant species can move from one area to another, crossing barriers that would normally stop or slow their spread. Non-native species are widely distributed along roadsides. Species commonly found along roadsides in southern Ontario include the invasive ecotype of the common reed (Phragmites australis), dog-strangling vine (Vincetoxicum spp.) and ragweed (Ambrosia spp.).
What Can Be Done?
Most ecologists would agree that prevention is preferable to mitigation. However, when the decision is made to build a road, there are several forms of mitigation that can be implemented. Wildlife fencing, underpasses/overpasses, warning signs, lower speed limits, highway lighting, and public awareness programs have all been used with varying levels of success. For instance, fences have been found to work well in certain situations, but not all. Based on studies of roads in North America, it has been recommended to use fences when traffic volume is so high that animals are almost never successful in their attempts to cross the road. The same study discourages the use of fences when animals need access to resources on both sides of the road, unless fences are used in combination with wildlife crossing structures. Ultimately, more research is required on what type of mitigation is appropriate in different situations and what is best for the wildlife and ecological integrity of the area.
One of the guides developed as part of the Ministry of Transportation’s (MTO) Environmental Standards Project is the Environmental Guide for Wildlife in the Oak Ridges Moraine (discussed in greater detail in Ministry of Transportation Environmental Standards Project and 2007 Review of Decision on MTO Environmental Standards Project in the Supplement to this year's Annual Report) which explores mitigation in detail. This guide is intended to help address the environmental protection requirements for the Oak Ridges Moraine, specifically those related to facilitating wildlife movement. While this document is not intended to apply across the whole of Ontario, it does summarize much of the best available information on mitigating the impacts of roads on wildlife.
MTO’s former Research and Development Branch completed a study on the effects of highway barriers on wildlife in 1995. Unfortunately, the branch was eliminated shortly after completing the study as a result of funding cut-backs, and MTO no longer undertakes original research. The MTO staff tries to keep up with the latest research being done elsewhere and applies it to their projects, but they are not in the business of monitoring wildlife. The one exception is Highway 69, where both the Ministry of Natural Resources (MNR) and MTO have partnered to undertake the monitoring of wildlife passages and barriers. This is a pilot project and there are currently no plans for long-term wildlife monitoring on other highway projects.
Monitoring of where wildlife crosses roads (or where they could cross proposed roads) is essential in order to be able to mitigate the impacts. Unfortunately, this is not occurring in Ontario in a centralized or cohesive manner. The Ontario Provincial Police (OPP) maintain statistics on the types of collisions that occur and note whether they involve a wild animal. This information is passed on to MTO’s Road User Safety Division and is published in the Ontario Road Safety Annual Report. In the past, it was not specific to the type of wildlife but, as of 2001, the data does specify if a collision involved a deer. However, any collisions with small animals are not monitored, and many of the migration corridors of reptiles and amphibians are unknown.
The Toronto Zoo has formed a road ecology group, made up of government and non-government scientists, educators and transportation planners. This group is working on a habitat connectivity analysis to help determine where the wildlife “hotspots” are for amphibians and reptiles based on mapping of wetlands and forests. They are also asking the public to send in their observations of either roadkill or live animals crossing the road. This will be overlaid with the various natural heritage systems that have been mapped in southern Ontario (e.g., Oak Ridges Moraine, Greenbelt, Toronto and Region Conservation Authority, etc.) and, ultimately, with mapping of future road upgrades and expansions from MTO and municipalities. The planning process for new roads, upgrades and expansions can occur decades before construction actually begins, so it is essential that this connectivity data be incorporated into the process as early as possible. While it is very laudable that the Toronto Zoo has taken the initiative to form this road ecology group, ultimately a public agency (namely MNR) will need to step up and take responsibility for making sure that the mapping is expanded to other sensitive regions across the province, continually updated and taken into consideration during the road planning process.
There is a strong and growing body of evidence that roads can have long-term negative impacts on wildlife and ecosystems. Ontario has not progressed nearly as far as some other jurisdictions in Canada, such as British Columbia, in setting policies and standards to avoid or at least mitigate these impacts (see the sidebar for details of a particular wildlife mitigation response on Vancouver Island, BC). Of particular concern to the ECO is the impact that roads will have on the ecosystems of the North as pressure increases to open up parts of the boreal forest to logging and mining, as well as the continuing pressure for more roads on the already fragmented and heavily impacted and stressed natural landscape of southern Ontario. There is a need to look at the environmental impacts of roads on the broader landscape rather than just focusing on a narrow strip surrounding the pavement. Providing this is done, the impacts of roads can be mitigated to allow natural processes to con- tinue to operate, while still providing a safe and effective way for humans, goods and services to be moved from place to place.
The ECO recommends that MNR and MTO collaborate to monitor wildlife crossings on existing roads to determine where mitigation is required and to work together early in the road planning process to identify areas where wildlife passages will be necessary.
|This is an article from the 2007/08 Annual Report to the Legislature from the Environmental Commissioner of Ontario.|
Citing This Article:
Environmental Commissioner of Ontario. 2008. "Roads - Pathways for Humans, Barriers for Functioning Ecosystems." Getting to K(No)w, ECO Annual Report, 2007-08. Toronto, ON : Environmental Commissioner of Ontario. 192-197.