Roads and railway lines are so ubiquitous across the European continent that it is becoming impossible to measure their ecological effects, according to a study published yesterday in the Proceedings of the National Academy of Sciences.
In the study, researchers calculated the distances to the nearest paved road or railway line throughout 36 European countries, the first time that such calculations have been made comprehensively across the entire continent.
Nearly one-quarter of the land in Europe is within 500 meters of transportation infrastructure, half is within 1.5 kilometers, and virtually all is within 10 kilometers, they found.
They also examined the effects of this infrastructure on wildlife, using Spain as a case study. Individual roads are well known to have negative effects on wildlife in the immediate vicinity, but it has been difficult to capture the impact of the transportation network as a whole.
To begin building their picture, the researchers overlaid the distance-to-road analysis with maps of the distribution of six wildlife species in Spain: Tawny owl, Great bustard, Spanish imperial eagle, Gray wolf, Iberian lynx, and Brown bear.
For all six species, most of their range is relatively near transportation infrastructure, simply because most of Spain’s land area lies in close proximity to roads and railways. Still, four species—the bustard, eagle, lynx, and bear—avoid areas within 500 meters of a road.
But even this avoidance can’t entirely buffer these species from the negative effects of roads. In 2014, 20 Iberian lynx out of a total population of 320 animals were killed by motor vehicles.
Next, the researchers applied a set of equations, describing how population densities of various species decline as they get closer to roads, to their data on the distribution of birds and mammals in Spain.
This analysis suggests that transportation infrastructure is affecting the abundance of birds across half of Spain’s land area, and the abundance of mammals across 95 percent. The researchers estimate that transportation infrastructure decreases the abundance of the average bird species by 19 percent, and decreases the abundance of the average mammal species by 43 percent.
Common sense says that the more extensive road networks become, the greater their effects on wildlife species. But paradoxically, the more extensive road networks become, the more difficult those impacts are to capture. “Researchers may no longer be able to measure the whole extent of road effects,” the authors write, “…because core areas of significant size that could be used as controls are now almost inexistent.”
But that’s not true everywhere in the world. Nine-tenths of all road building within the next 40 years is predicted to happen in developing nations. The methods used in the study could help planners minimize the ecological effects of future development in these areas, many of which host species-rich tropical ecosystems, the researchers say. – Sarah DeWeerdt | 12 July 2016
Source: Torres A. et al. “Assessing large-scale wildlife responses to human infrastructure development.” Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1522488113
Header image: The density of transportation infrastructure in Europe. Credit: Marina Pinilla.