Rapid assessment of linear transport infrastructure in relation to the impact on landscape continuity for large ranging mammals

Many Eastern European countries still host landscapes with high value due to their habitat quality and size. Some of these countries are new member states of the European Union, and EU-accession is accompanied by huge investments in the development of traffic infrastructure. Environmental assessments mandatory for road constructions in the EU do not necessarily require explicit measures for the mitigation of fragmentation, and technical constructions associated with road building are frequently assumed to provide sufficient possibilities for wildlife crossings. We evaluated those technical structures at two motorway sections separating relevant subpopulations of the brown bear (Ursus arctos) in Bulgaria. Our assessment revealed that the permeability of the two motorways has been considerably overestimated. A total of just 13 out of the 77 potential crossing possibilities of the two roads together meet the requirements we defined for suitable wildlife crossings. We found that the potential for improvement of the crossing functionality of already existing technical facilities along the motorways is very limited. Given the dependence on a small number of habitat paths connecting suitable crossings with habitat on both sides of the road, connectivity between subpopulations is vulnerable to fragmentation impacts.