Roadside spaces represent valuable and well-connected habitats for many animal species on the one hand. On the other hand, traffic routes cause losses due to collisions, pollutant emissions and noise. It is usually unclear whether positive or negative effects predominate and whether they can influence the entire population. If negative, population-relevant effects predominate, in extreme cases individuals could be attracted to the road from habitats unaffected by traffic, thus weakening the entire population.
The objective of the present study was to investigate the relevance of such an indirect trapping effect in roadside habitats and to derive any necessary minimization options. For this purpose, population-ecological and partly genetic studies were carried out for the species hazel dormouse, Eurasian blackcap and the butterflies small heath and European common blue along a freeway and a busy road, respectively, over a period of three years.
No indirect trapping effects in roadside habitats were documented for any of the species. With respect to the dormouse, a comparison of densities of near-road and far-road populations indicated that near-road habitats may be of higher or equal value compared to far-road habitats. Genetic studies also demonstrated that dormouse populations are vital in roadside groves and use them as dispersal axes. For blackcap, the determined territorial densities and breeding success of populations near roads were not generally lower than those far from roads. For the butterflies, especially the common blue, it could be shown that populations close to the road cannot be genetically distinguished from populations far away from the road. Population sizes or densities were also similar, although adult butterflies probably suffered increased mortality in roadside habitats than in habitats unaffected by traffic. However, this did not negatively affect populations.
Despite traffic-related impairments, it consequently makes sense to implement measures to promote biodiversity in roadside spaces. In this context, a high habitat suitability, sufficient width as well as the best possible connectivity play an essential role. Nevertheless, due to the existing impairments, they cannot be seen as adequate substitute habitats for ecologically valuable habitats.
BMVI - Issue 1139; Available here: https://www.schuenemann-verlag.de/fachverlag-nw/neuste-produkte/unterstuetzung-der-unfallkommissions-arbeit-durch-einen-webbasierten-massnahmenkatalog-zur-beseitigung-von-unfallhaeufungen-5369.html