Talk The habitat value of power line rightsofway for pollinators bees and butterflies in agricultural landscapes

To ensure safe transport of electricity, the vegetation in power line rights-of-way (ROWs) must be maintained low. In wooded areas, the construction and maintenance of power line ROWs thus require regular clearings that can have negative ecological effects on forest species through the fragmentation of continuous forest habitats. However, this also creates open areas that may be suitable to plant and animal species associated with open habitats such as grasslands or moors. The value of these open areas for biodiversity has rarely been studied, especially for insect pollinators. Maintaining suitable pollinator habitats in agricultural landscapes is an important issue due to their vital role in pollinating many crops and wild plants.

Here we assessed the value of power line ROWs as habitat for pollinators by comparing assemblages of bees (Hymenoptera, Apoidea) and butterflies (Lepidoptera, Rhopalocera) with those found in typical pollinator habitats in neighbouring agricultural landscapes, i.e. semi-natural (extensively managed) grasslands. We also surveyed the availability of food and nesting resources to better understand the drivers of bee and butterfly abundance, species richness and assemblage composition in ROWs.

The study was carried out in central France, near Limoges (45°51’N, 1°15’E), in 31 power line ROW sites and 25 grassland sites. Bees and butterflies were surveyed by sweep netting in suitable weather conditions during 40-min transect walks. Regarding the availability of food and nesting resources, the following variables were considered: flowering plant cover and species richness, shrub cover, vegetation height, bare ground cover, and presence of dead wood.

A total of 109 and 78 bee species were collected in the power line ROW and grassland sites, respectively. Bee abundance and species richness were higher in power line ROW sites than in grassland ones. A total of 59 and 50 butterfly species were found in the power line and grassland sites, respectively. The mean number of butterfly species was not significantly different between the two groups of sites.

We also identified key environmental factors affecting bee and butterfly assemblages in power line ROWs. The cover and species richness of flowering plants and the availability of nesting sites for both above ground and below ground nesting bees positively affected bee species richness and abundance. On the contrary, shrub cover (especially ferns) negatively affected bee species richness and abundance as well as butterfly species richness.

The composition of bee and butterfly assemblages in power line ROW and grassland sites will also be analysed from both taxonomic and functional approaches, and considering species status (rare vs. common species).

Overall, our study indicates that power line ROWs are valuable habitats for pollinator conservation in agricultural landscapes. As management recommendations, we suggest to maintain patches of bare ground and not to remove dead wood resulting from management interventions, at least small branches. Moreover limiting fern cover could enhance flower abundance and diversity.

bees, butterflies, flowering plants, power line rights-of-way, grasslands, rare species, ecological traits, species richness, France