During the last few decades, the construction of wildlife passages and landscape bridges designed to help fauna cross transport infrastructures has increased all over Europe. A lot of information is currently available about the characteristics of the structures that determine their effectiveness as fauna passages for different target species. In many countries, handbooks and norms have provided technical instructions and recently this information has been compiled in the handbook COST 341. Wildlife and Traffic. A handbook on identifying conflicts and designing solutions (Iuell et al 2003). Nevertheless, one difficulty that remains is the identification of the best locations for these structures, which means identifying wildlife corridors and those places more intensively used by different target species during their movements.
A model based on landscape features GIS analyses (DISPERSA model) has been developed and is currently being tested in Catalonia, in the North Eastern Iberian peninsula. The basis for the analyses was provided by a previous field research that identified relevant habitat and landscape features associated with bird and medium-size mammal abundance during dispersal and periods of high movement activity which in this area coincides with the autumn. Using a multivariate method, the study established that some features exist which were associated with higher species abundance (Brotons and Rosell, 2001).
The DISPERSA model analyses different landscape attributes, assigning different values depending on three combined characteristics: type of land cover, relief structure (linear guide-ways, such as presence of ridges and valleys) and presence of streams. By means of the GIS analysis, an index of wildlife dispersal interest is assigned to each part of the territory, and identifies sectors with a high index value where an increased presence of animals is expected, especially during dispersal and high mobility periods.
The maps generated by this means of analysis allow the identification of existing barriers and dispersal wildlife corridors and also the determination of the location of conflict points when a new infrastructure is overlapped. In case that the affection of these wildlife corridors cannot be avoided by changing the route, the conflict points will require the adoption of measures aimed at helping wildlife to cross and maintaining the connections between adjacent habitats of both sides of the infrastructure. It must be emphasised that the response to the landscape features depends on the target species. For this reason, it is fundamental to identify clear target species when the analysis is carried out in order to provide an effective assessment tool for the identification of the location of the most sensitive places where measures must be adopted to ensure the linkages between core areas and to facilitate their functional connection.
Spain
