Assessing the potential of linear infrastructure verges for conservation and dispersal of wild pollinators in landscapes The PolLinéaire approach

Pollinators are declining worldwide, leading to question whether a global pollination crisis is underway. This would result in severe consequences for man and nature as most crop and wild plant species depend on animal pollination. This decline is due to multiple interacting factors, mostly bound to agriculture and urbanization, but the transportation sector has its share of responsibility as linear transport infrastructures (LTI) are notably responsible for habitat loss, fragmentation and pollutant release.

In practice, such impacts are considered by Environmental Impact Assessment studies, which regard mainly the conception of LTI projects and the construction stage. Nevertheless, LTI in operation keep important surfaces of green verges which, under suitable management, might serve to improve their overall environmental balance sheet. Yet, the potential benefits of LTI verges for pollinators and the potential pollination service they provide to the surrounding landscape mosaic have scarcely been assessed. Their proper management could result in a better environmental integration of LTI into landscapes (contribution to green networks, support to agro-ecology).

The PolLinéaire project (2014-2016) aims at assessing, explaining - and making operational proposals to develop - the potential of green verges as habitat and source of pollinators (Hymenoptera, Apoidea and Lepidoptera, Rhopalocera). Typical site configurations were defined in order to study the habitat (nesting resources, food availability) and the source (displacements) functions. Western France was investigated for study sites bound to national roads, railways, waterways and powerline networks.

In order to assess lateral displacements, entomophilous crops adjacent to LTI were searched. The habitat function was more extensively studied thanks to LTI implanted into forest cuts in the most forested part of the investigation area (Limoges region, 45°51’N, 1°15’E). The preliminary search for relevant areas was carried out by means of the BD Topo database (2014) for LTI networks, the RPG database (2012) for crops, and the BD Forêt database (2014) for afforestation. When necessary, network operators were consulted for information and to access sites for check-up (e.g. crop rotation).

An oilseed rape (OSR; Brassica napus) production area was selected with crops adjacent to a set of national road sections (north-west). Field work was carried out during OSR flowering on 6 sites. Insects were identified on-site (butterflies) or collected (sweep netting) for identification by experts (wild bees) along a 1-km long section of green verge, and within the OSR field. A set of 31 power line rights-of-way (ROW) sections was selected as study sites in the forest area. Insects were also identified/collected in 25 grassland sites located less than 1 km away from the ROW sections for comparison purpose.

LTI networks irrigate all areas under man’s influence. At a regional/country scale, green verges constitute a very large surface. PolLinéaire is a first step to improve knowledge on their potential benefits for pollinators. In order to gather more information and to answer faster the worldwide concern about pollinators and insect pollination, this methodology could be applied to many kinds of LTI networks in different biogeographic areas in the world.

wild bees; butterflies; flowering plants; road verges; power line rights-of-way; methodology; France