Transport corridors, such as roads and railroads, have been shown to be major causes of habitat fragmentation. They not only cause the loss of natural habitats but also affect the quality of adjacent habitats, inhibit animal movements and, last but not least, increase unnatural wildlife mortality due to collisions with traffic.
The main objective of the project was to develop a long-term programme for defragmentation measures at transport corridors in Bulgaria in order to restore ecological networks and preserve biodiversity. This included:
- strengthening interinstitutional cooperation at the national and regional level on transport-ecology issues;
- improving implementation of transport-ecology issues in EIA statements and guidelines for the development and design of transport networks;
- institutionalizing the exchange of knowledge and best practices between experts from Bulgaria and other European countries to mitigate and compensate ecological impacts of the expansion of transport networks;
- raising political, administrative and public awareness on the impacts of habitat fragmentation due to transport corridors in Bulgaria.
To identify bottleneck locations in the Bulgarian road and railroad network we used a combination of two strategies. First, an expert-based GIS model was used to study the impact of existing and planned human transport corridors on the viability of wildlife populations. Second, experts were consulted for their opinion of important ecological bottleneck locations.
Two methods were included and combined in the study, as the development of a national program for de-fragmentation in the Netherlands
It has shown that bottleneck location are best assessed when model analyses of the viability of wildlife populations on a national scale are combined with expert knowledge of the local situation.
Many wildlife species are affected by roads. Since it would not be feasible to analyze all the species in Bulgaria that might be sensitive to road impacts, twelve key wildlife species were selected and used as indicators to assess bottleneck locations in Bulgaria’s transport network. The species were selected so as to represent all the major ecosystem types in the country. Moreover, a range of small, medium and large animal species were selected, as the barrier effect of roads can vary according to the size of the species, the size of their home ranges and their ability to move between habitat patches. The selection consisted of 8 mammal, 3 reptile, and 1 amphibian species.
Policy makers and transport planners increasingly recognize the problem of habitat fragmentation by transport corridors. Preventing impacts is preferable to mitigating impacts. In the planning of all road projects, either road construction or upgrading, the first step should be to explore how to avoid impacting ecologically sensitive areas and important wildlife corridors. The remaining impacts should be addressed through mitigation measures. The barrier effect of roads and railroads, as well as wildlife mortality due to collisions with traffic, are usually mitigated by the construction of wildlife crossing structures, such as wildlife overpasses or underpasses, in combination with wildlife fences that guide the animals towards the passages and keep them off the roadway.
Studies have shown that such measures are frequently used by a variety of wildlife species. Impacts that cannot be mitigated should be compensated through habitat restoration at a different location.