Group of red-legged partridges on a road in Aznalcázar, in the province of Seville. Photo: Jacinto Román

Global infrastructure development continues at a rapid pace. By 2050, an additional 3 to 5 million kilometres of roads are expected to be built, along with a 26% increase in the global railway network, and millions of new kilometres of power lines and gas pipelines. Many of these new infrastructures will be deployed in regions of high biodiversity, such as the African continent and Southeast Asia.

In this context, an international team of scientists, including researchers from the Doñana Biological Station – CSIC, warns of a major shortcoming in current environmental impact assessments: the lack of consideration of fauna abundance as a key indicator for measuring the true impact of linear infrastructures (such as roads, railways, and power lines) on biodiversity.

Currently, many assessments focus on indicators that provide limited information, such as counts on counts of animals killed on a road or the number of individuals using a wildlife crossing. “Although these monitoring efforts are often carried out systematically, their limited duration or focus on specific aspects can offer a partial view of the actual impact infrastructure on wildlife and may lead to misinterpretations,” explains Marcello D’Amico, a researcher at the Doñana Biological Station.

For example, a low roadkill rate does not necessarily indicate a low impact. It could be the result of a population decline due to previous high mortality, or because animals avoid areas near the infrastructure, leading to fewer collisions. This can have serious consequences for the structure and viability of wildlife populations.

“To make this data useful, we need to translate it into meaningful indicators, such as per capita mortality or the proportion of animals crossing in relation to the total local population. For that, it is essential to have an estimate of the population size living near the infrastructure being assessed,” explains Rafael Barrientos, a researcher at the Complutense University of Madrid.

However, this essential data is usually missing from most assessments. Among the reasons are the lack of retrospective evaluation in many public works -which would allow for a better before-after comparison- and the short- or medium-term design and construction of infrastructures, which limits the time available for comprehensive assessment. 

The scientific team also emphasizes the importance of analyzing the temporal evolution of population abundance. A decline in the number of individuals within a population can have drastic consequences in the long term. Smaller populations lose reproductive potential and genetic diversity, making extinction more likely. For this reason, the researchers stress the impacts should be assess not only based on immediate effects, but also on their implications for the future viability of affected populations. 

In response to this situation, the scientists propose incorporating systematic measurements of abundance before and after constructions into environmental assessments, using solid designs that include control areas. Although the ideal goal would be to evaluate the long-term population survival, they acknowledge that, in practice, focusing on changes in abundance may be a more feasible and representative approach. They suggest that, at least for certain key species, studies should analyze population trends in relation to the presence of infrastructures.

“If we don’t understand the impact these infrastructures have at population levels, we are limiting our ability to assess them and, as a result, we are underestimating the risks their development poses to biodiversity conservation”, says the researcher Marcello D’Amico.

The article is authored by researchers of the Complutense University of Madrid, the University of Lisbon, the Carlenton University of Canada, the University of Rio Grande do Sul in Brazil and the Doñana Biological Station – CSIC.

Reference

Rafael Barrientos, Fernando Ascensão, Lenore Fahnig, Fernanda Zimmermann Teixeira, Marcello D’Amico. Population abundance should be an Essential Biodiversity Variable in infrastructure impact assessment. Environmental Impact Assessment Review 115: 108021. https://doi.org/10.1016/j.eiar.2025.108021