Impacts of pairing transport infrastructures on composition and structures of landscapes and on functional connectivity of ecological networks

Major transport infrastructures (i.e. high-speed railways, highways) are known to have major impacts on landscape transformation, including ecological habitat fragmentation. Their developments in past and future decades make this phenomenon worse. In order to reduce the negative effects of such constructions, the pairing of such transport infrastructures has been proposed. For the moment, pairing processes have been asynchronous: i.e. first of all construction of a high-speed railway, and few years or decades later, pairing of a new highway (or the reverse order). In that context, our study aims to test the impacts of the different stages of constructions on landscapes.

In that way, two case studies of paired transport infrastructures were studied in France, both in a context of farming landscapes. We focused our study on three stages: first stage before the first infrastructure construction; second stage after the first infrastructure construction (in order to evaluate its impacts); third stage after the pairing of the second infrastructure (in order to evaluate the impacts of pairing). Several analysis methods were used in order to comprehend and measure the landscape changes at these different stages. We firstly compared the global landscape composition at the three stages, and we measured which kinds of habitats were destructed by the constructions. We then measured more accurately the changes in landscape composition and structure (landscape metrics) in concentric buffers around the transport infrastructure constructions. Finally we carried out a functional analysis/modelling of ecological networks (forest habitats and herbaceous habitats were focused) for several species with different dispersion capabilities. ArcGis (10.2) and Fragstat were used for GIS and landscape metrics analyses; Spatial Analyst ArcGIS Extension was used for modelling ecological networks.

The results of our study cases show that the major impacts on landscape composition and structure are due to the construction of the first transport infrastructure; particularly important changes in fragmentation level are induced by this first infrastructure. These results are similar whatever the order of construction and pairing (one of the study cases: first the railway then the paired highway or the other case: first the highway then the paired railway). Nevertheless results on landscape functional connectivity are quite different if they are focused on herbaceous habitats (connectivity increase because of increase of herbaceous habitats along infrastructures) or on forest habitats (decrease of connectivity).

These results are consistent with the hypothesis that the approach of pairing transport infrastructures is a good opportunity to avoid drastic ecological changes in landscape. However we hypothesize that it should be much more effective if the construction of the two paired infrastructures would be synchronous (potential decrease of costs; common reflections on mitigation measures and their impacts on biodiversity and landscapes).

Landscape Ecology, Road Ecology, Fragmentation, Landscape metrics, Pairing Transport Infrastructure, Functional Connectivity