A safe, efficient and well-connected transport system is usually perceived as a key to a prosperous future. Modern economies, markets and societal structures depend heavily on the transport of people and goods. Similarly, populations of wildlife need the exchange and communication with neighboring populations to sustain persistence. Mobility is in fat an intrinsic property of life itself and thus an essential requisite also in ecology. The important difference between humans and wildlife is that they now use competing infrastructures.
Modern transport systems with their supporting infrastructure entail substantial environmental impacts. They consume non-renewable natural resources including our most limited asset: space. The transport sector is one of the main drivers in the global loss of biodiversity, both directly, by affecting natural living spaces, and indirectly, by preparing for other sectors to spread and exempt natural resources. Furthermore, transportation stands for about 20% of the global carbon dioxide emissions and contributes significantly to climate change and air pollution.
Traffic is responsible for the death of hundreds of millions of wild animals in Europe each year. Some endangered groups of species, such as amphibians and large carnivores, are especially exposed and sensitive, but also among common wildlife species, the toll of traffic can be substantial and locally a threat to management and survival of the species. Collisions with larger wildlife, such as wild boar or deer, are known to produce a considerable economic cost to drivers and transport operators. Less well known is that even in railway traffic, especially high speed systems, collisions with larger animals can cause expensive repairs and extensive delays.
Many species are killed in traffic in their attempt to cross the road or railroad, and those that not even try may suffer from barrier effects. Transport corridors impose movement barriers both directly, through their physical presence and attributes such as fences or gullies, and indirectly, through traffic mortality, repellence and avoidance. Barriers can entail undesired changes in the abundance and resilience of wildlife populations, on their genetic exchange and viability, and ultimately, on biodiversity at large.
Traffic noise, light, invasive species, chemicals and particular matter, and various other disturbances spread from infrastructure into the adjacent landscape and degrade living conditions for both wildlife and humans.
Thus, even if the area physically consumed by roads or railroads may be seemingly small, traffic and infrastructure affects an area that is substantially, may be more than 20 times, larger. Effects at large scale and on ecosystems are substantial – and universal! Practically all countries face similar problems and look for similar solutions.
There is hence still a need to improve our understanding of the complex pressure of transport infrastructure on wildlife populations and the environment. Authorities ask for adequate methods to predict, evaluate, and counteract adverse effects, and implement this knowledge into the planning and maintenance of transport infrastructure in order to meet sector-level policies on sustainable development and conservation of biodiversity. Mitigation concepts are needed that operate at both strategic and project planning level and can affect the underlying causes as well as the resulting effects and consequences to populations and society. In many cases, dose-effect relationships need to be quantified and potential thresholds identified, before adequate mitigation can be chosen and eventually implemented. Existing ecological knowledge must be combined with economic and social sciences to achieve a holistic approach that allows the whole range of ecological factors operating across the landscape to be integrated within the planning process. This does not apply solely to the planning of transport infrastructure, but likewise to all exploitation and management of natural resources…
Schematic representation of the five primary ecological effects of infrastructure: Habitat loss and transformation; disturbance due to pollution and edge effects; barrier and avoidance; mortality due to traffic accidents and predation; and the conduit or corridor effect. Together, the various primary effects lead to the fragmentation of habitat (COST-341 European Review).
Habitat loss – The construction of roads and railroads always involves a net loss of wildlife habitat. The physical encroachment on the land causes disturbance and barrier effects in the adjacent and wider environment that further decrease the amount of habitat that is suitable or available for wildlife.
Disturbance/Pollution effects – Transport infrastructure disturbs and pollutes the physical, chemical and biological environment. Toxins, edge effects and noise affect a much wider zone than that which is physically occupied. Road and rail verges can represent a trap for predatory animals and forest fires frequently originate here.
Barrier – For most non-flying terrestrial animals, infrastructure represents movement barriers that restrict the animals’ range, make habitats inaccessible and can finally lead to an isolation of populations. The barrier effect is the most prominent factor in the overall degree of fragmentation seen to be caused by infrastructure. Road mortality and the disturbance effect contribute to the barrier impact.
Habitat – Road verges and roadsides can provide new habitats that to some degree compensate for the loss and disturbance of the original habitat. However, the effect can be either positive or negative depending on the context: positive in already heavily transformed low diversity landscapes, non-existent or negative in natural well conserved landscapes where the invasion of non native, sometimes pest species, can be facilitated.
Mortality – Millions of animals are killed on roads each year in Europe. The numbers of road kills are steadily growing, but for most common species, traffic mortality it is not considered as a severe threat to population survival. Some animals, however, are more significantly affected by road mortality than others.
COST 341 – Habitat Fragmentation due to transportation infrastructure: The European Review. Office for Official Publications of the European Communities, Luxembourg, pp. 31-50. SoA_SE-final2003.pdf
(c) Andreas Seiler