Restoring Ecological Networks across Transport Corridors in Bulgaria

Bulgaria is currently in a phase of political and socio-economic transition and faces many challenges in balancing economic and environmental interests. One of these challenges is the development of a sustainable road and railroad network that facilitates the need for efficient transport of goods and people but does not threaten areas that are especially valuable for nature conservation. Currently plans have been developed to substantially upgrade and expand the national road and railroad network. The existing transportation corridors and the proposed extensions pose a threat to wildlife and affect the development and functionality of both a national and Pan-European ecological network. The authors objective is to provide the necessary knowledge to help the Bulgarian authorities set up a national program to minimize the fragmentation effects of these expanding transportation corridors so as to preserve biodiversity and develop a coherent and sustainable ecological network across the country. The main research questions the authors addressed are: (1) What sections of the road and railroad network are expected to significantly affect the viability of wildlife populations? (2) Which of these ecological bottleneck locations need to be addressed most urgently? (3) What measures could be taken to solve the problems? To identify bottleneck locations in the Bulgarian road and railroad network the authors used a combination of two strategies. First, an expert-based geographic information system (GIS) model – LARCH – was used to study the impact of existing and planned human transport corridors on the population viability of twelve indicator species. Second, and independent of the modeling approach, experts for all indicator species were asked to identify bottleneck locations in the road and railroad network in Bulgaria. The bottleneck locations identified by the LARCH model and the experts were mapped and analyzed for potential overlap. In total 283 bottleneck locations were identified in the existing road and railroad network of Bulgaria. About 30% of all bottlenecks are classified as high priority locations. Immediate action is recommended at these locations as these have been identified as locations where the impact on population viability is high and/or wildlife is frequently killed in traffic. In total 544 mitigation measures were identified as necessary to restore habitat connectivity and reduce wildlife mortality. A significant number (331) of these proposed mitigation measures involve adapting existing structures, such as road tunnels, viaducts or bridges, to allow for better use of these structures by wildlife. In addition 213 new structures, to be used exclusively by wildlife, are needed. Total costs of the proposed mitigation actions are estimated to be 132 million euro. The implementation of the here proposed road and railroad mitigation is expected to significantly improve the population viability of most threatened wildlife species and, as such, is an indispensable first step in preserving Bulgaria‟s biodiversity and developing a coherent and sustainable ecological network across the country.