Roads, railways, and power lines: Are they crucial for bees in urban woodlands?

Abstract

The loss and transformation of habitats due to human impact are commonly regarded as major factors decreasing the diversity of pollinators. However, there is also some evidence that industrial infrastructure can play a positive role in shaping the composition of many animal communities. Still, little is known about how artificial linear structures, such as roads, railways, and electric power lines, affect the abundance and diversity of wild bees in urban ecosystems. Thus, we attempted to verify which of the habitats mentioned above is crucial for the occurrence of bee species of various functional groups. We conducted field research in woodlands of the city of Bydgoszcz (northern Poland). Site conditions were evaluated on the basis of phytoindicators (plant indicator species). In the study area, we recorded 32 % of all bee species reported from Poland. In respect of species richness and abundance, the habitats along railway lines were the most attractive to bees. Besides, in respect to bee species richness, these sites were the most similar to roadsides. The habitats located under power lines were the poorest in species. About 20 % of bee species were recorded only along railways and 3 % only along roads, while no bee species was recorded exclusively under power lines. Bee species richness and abundance increased with growing cover of the sites by bee food plants and an increasing proportion of bare soil. Moreover, bee abundance increased with an increasing share of plant indicator species of very dry or dry soils and of alkaline soils. Bee abundance declined with an increasing share of plant indicator species of sandy soils. The presented results indicate that roads, railway lines, and power lines, in structurally simplified and floristically poor pine forests, are important for wild bees in urban ecosystems.