Transport infrastructure is so widespread in Europe that half of the land area is within 1.5 kilometres (km) of paved roads and railway lines, researchers have calculated.
The researchers found that in Spain, transport infrastructure has an impact on the abundance of birds in almost half of the country and is affecting the abundance of mammals across almost all of the land area.
The biggest threat to terrestrial biodiversity comes from habitat loss and degradation, driven by human development, especially building settlements and roads. The challenge is to preserve biodiversity and vital ecosystem services in the face of continued infrastructure expansion.
This study is the first to assess the extent of transport infrastructure across Europe and the large-scale effect that built infrastructure has on wildlife populations.
Using a pan-European database of geographic information, the researchers measured the distance of land areas to the nearest paved road or railway line in 36 European countries. They found that human infrastructure is so prevalent that nearly one quarter of land in Europe is within half a kilometre of transport infrastructure, one half of the land is within 1.5 km and almost all of Europe is within 10 km of a paved road or railway line.
Then, using Spain as a case study, the researchers assessed how the prevalence of built infrastructure affects bird and mammal wildlife. They first calculated the nearest distances to all built-up areas, impervious surfaces and paved road and railway infrastructures and also used a more precise and complete national database. They found that, on average, half of all land in Spain is within approximately 1.5 km of a built-up area, a bit less than 900 m from a road or railway line, and less than 750 m from an impervious surface. The researchers consider that the European estimates are very conservative, since using a more precise database for Spain revealed that transport infrastructure was most likely underrepresented in the pan-European database. Thus, the distances to the nearest transport infrastructure in Europe are likely shorter than their estimations from the pan-European database.
To assess how proximity to the built infrastructure affected the distribution of six iconic species of birds and mammals, the researchers overlaid maps of built infrastructure on distribution maps of tawny owl (Strix aluco), great bustard (Otis tarda), Spanish imperial eagle (Aquila adalberti), grey wolf (Canis lupus), Iberian lynx (Lynx pardinus), and brown bear (Ursus arctos).
Since so little land is far from a transport infrastructure, all six species were found relatively close to roads and railway lines. Nevertheless, the great bustard, Spanish imperial eagle, Iberian lynx, and brown bear all tend to avoid the closest 500 metres next to a road or railway line. The Spanish imperial eagle, Iberian lynx, and brown bear, in particular, are all more prevalent at locations further from transport infrastructure, indicating their preference for more remote areas, or that they were able to survive only in those areas.
In 2014, 20 critically endangered Iberian lynxes, out of a population of approximately 320 (over 6%), were killed on the roads in Spain, illustrating the large-scale impact that roads have on roaming species.
The researchers then used data from an earlier meta-analysis to model how the abundance of Spanish birds and mammals was affected by proximity to the built infrastructure. They predicted that the presence of roads and railways lines, for example, reduces the overall abundance of birds by 19% and the abundance of mammals by almost 47% compared with undisturbed areas.
The maps revealed that, compared with undisturbed areas, built infrastructure reduce the abundance of the birds across 55.5% of the Spanish land area and the abundance of mammals across almost all (97.9%) of the land. The influence on the abundance of wildlife of paved roads and railways alone is similar (reduction by almost 50% for birds and 96% for mammals).
Across Europe, the researchers say areas unaffected by paved roads are so small that scientists may no longer be able to compare the impacts of road developments with undeveloped 'control' areas, particularly for wide-ranging mammals and birds.
The researchers suggest that their approach may be used to identify priority conservation sites in areas that currently contain little infrastructure, e.g., roadless areas, before they are lost to development. Past and ongoing habitat losses may lead to the future potential extinction of some species, which is not yet evident. Conservation efforts should, therefore, include securing existing habitats, strengthening remaining species and restoring essential ecosystem services to prevent threatened species from becoming extinct through the expansion of infrastructure development.
With their study focused on Spain and much of their data taken from European research, the researchers say their approach to assessing the impact of infrastructure on wildlife would be particularly useful in regional and national infrastructure planning in other European areas. The results of the study confirm the need to enhance actions to reduce habitat fragmentation and to adopt corrective measures for reducing collision risks on existing roads and infrastructures.
However, less economically developed countries are set to build nine-tenths of road developments in the next 40 years. Many of these areas, such as tropical forests, are still rich in biodiversity and the researchers say their approach can also be used for planning scenarios and regulating infrastructure expansion and helps to develop mitigation measures that reduce the negative impacts of built infrastructure on wildlife in these places.
Therefore, the researchers are calling for the development of an internationally coordinated database and for studies on the impact of infrastructure on wildlife across a range of ecosystems and geographical areas, particularly in developing economies.
Source: Torres, A., Jaeger, J.A.G. & Alonso, J.C. (2016). Assessing large-scale wildlife responses to human infrastructure development. Proceedings of the National Academy of Sciences, 113 (30): 8472-8477. DOI:10.1073/pnas.1522488113