Talk TRANSFER project railways ecological transparency

SNCF Réseau is one of the major transport infrastructures manager in France. It is in charge of 30 000 Km of railway lines, their development and their upgrading. Within the framework of the green and blue belts, the transport infrastructures are identified as one of the main causes of the fragmentation of ecological continuities.

Specific construction works have been made during the last thirty years to secure crossing of wild animals. Their efficiency is monitored through surveys but protocols are not yet standardized and they focus on big mammals, carnivores and amphibians.

In addition to the eco-bridges built on new railway tracks, there is an increasing demand to restore the ecological continuity on the existing network. The main problem is that we really know little about the transparency of the infrastructures and the global efficiency of these specific engineering works.

In this context, an assessment of the transparency of railway infrastructures has been engaged with the assistance of the Ministry of the Environment. The aim is to assess the role of various crossing works existing on the national network and to define a first list of measures aiming at restoring the ecological continuities and their surroundings.

The chosen methodology involves studying four railway sections, each one about twenty kilometre-long : two of them within totally enclosed TGV railways, the others within conventional railway tracks. All are located in the North-East of France, and cross a huge proportion of mixed forest and agricultural landscapes.

Standard survey methods were used : camera traps for many terrestrial mammal species and ultrasonic sound recorders. The analysis of events on the different types of crossing works (almost 480,000 photos and 68,000 ultrasonic recordings) has been carried out in order to treat all data globally according to different criteria (human frequentation, size of crossing works, seasonal variations…). Thus, it provides reliable information on the regular mobility of individual animals on each side of infrastructures.

In parallel, landscape genetic was used via molecular technologies. Analysis on DNA samples from individuals of many populations located on both sides of the sections enabled to measure the degree of fragmentation of  tracks and the genetics flows of 3 species : an amphibian (Salamandra salamandra), a butterfly (Maniola jurtina) and a beetle (Feronia nigrita). Genetical distance measured between populations enabled a rigorous diagnosis of the permeability thanks to a specific focus on the functional connectivity, integrating landscape effects.

Whatever the survey methodologies used, the results of this project indicate that railway tracks do not generate any impassible barrier for the studied species. As a matter of fact, they play a filter function: for instance, they create local difficulties for the ungulates when the tracks are enclosed.

barrier effect, genetic analysis