Road verges support pollinators in agricultural landscapes, but are diminished by heavy traffic and summer cutting

Abstract

Supporting pollinators in agricultural landscapes is important for reversing their global decline. Road verges and hedges are used by pollinators for feeding and reproduction, but few studies consider entire pollinator communities, and it remains unclear how they are distributed across adjacent verges, hedges and fields, or how they are affected by traffic and verge cutting. We surveyed flowers and pollinators, using transect counts and pan traps, to explore the role of road verges and their associated hedges in supporting pollinators in an agricultural landscape in southwest England, and the impacts of traffic and verge cutting. At 19 sites, we surveyed the road verge (verge edge and verge centre), the verge hedge (both sides), a field hedge and the field interior. Road verges and hedges had a much greater flower abundance, flower species richness and pollinator abundance than field interiors. Verge hedges had far less woody cover than field hedges, but greater flower species richness. There were fewer pollinators along verge edges (next to roads) than along verge centres (2–11 m from roads) and fewer pollinators in road verges next to busier roads. Road verges were generally cut once (in summer), and cuttings were never removed. There were substantially fewer flowers and pollinators in road verges that had been cut, even though surveys often took place many weeks after cutting. Synthesis and applications. Road verges and their associated hedges can provide hotspots of resources for pollinators in agricultural landscapes, but their capacity to do so is reduced by heavy traffic and summer verge cutting. We recommend that beneficial management for pollinators should prioritize wider road verges (at least 2 m wide), roads with less traffic, and areas away from the immediate vicinity of the road. Where possible, verge cutting should not be carried out during peak flowering times.

Roadside diversity in relation to age and surrounding source habitat: evidence for long time lags in valuable green infrastructure

“…On the other hand, modern road verges appear to still be in the colonisation and establishment phase and have the potential to develop and gain further species in the future (Isbell et al., 2019; Spooner & Smallbone, 2009). How many species could be gained is likely to depend on other factors such as road verge width, structure and road traffic intensity (Angold, 1997; Jimenez et al., 2013; Phillips et al., 2019), factors which can also covary with road age. Further study across a gradient of different road ages would give a greater indication of the rate build‐up (or gradual loss) of species and specialists over time.…”

“…Ideally, as much road verge habitat as possible should be managed for biodiversity, but if practitioners want to identify the most species‐rich verges then we recommend the use of historical maps to find those stretches of roads that are older than 100 years. Although a discussion of appropriate management strategies is beyond the scope of this study, verge cutting at the appropriate time to benefit both plants and pollinators, plus hay removal is likely to have the most positive effect on biodiversity (Jakobsson et al., 2018; Phillips et al., 2019). Due to the apparent long time lags in community assembly, seed sowing can be an option to increase roadside diversity (Auestad et al., 2016), even for road verges that were established several decades ago.…”

“…Such habitat elements are generally kept open by cutting and clearing vegetation for practical or safety reasons and can therefore provide habitat for grassland species. Roads, and road verges in particular have received a lot of attention, being found to provide habitat for multiple taxonomic groups in different regions of the world (Bellamy, Shore, Ardeshir, Treweek, & Sparks, 2000; Hopwood, 2008; Lindborg, Plue, Andersson, & Cousins, 2014; O'Farrell & Milton, 2006; Phillips, Gaston, Bullock, & Osborne, 2019; Spooner & Smallbone, 2009).…”

Can linear transportation infrastructure verges constitute a habitat and/or a corridor for vertebrates in temperate ecosystems? A systematic review

“…Insect abundance was even higher on non-highway road verges than away from roads. Similarly, a recent study showed that road verges and their associated hedges can provide hotspots of resource for pollinators in agricultural landscapes, but their capacity to do so is reduced by heavy traffic (like on highways) [23]. The aim of the present paper was to complement the previous work on insects published by Villemey et al [22], focusing this time on vertebrates (mammals, birds, amphibians and reptiles).…”

Enhancing road verges to aid pollinator conservation: A review

“…Road verges are often important early or mid-successional habitats providing feeding and reproductive opportunities for pollinators including diverse floral resources (e.g. Halbritter et al, 2015;Noordijk et al, 2009;Phillips et al, 2019) and larval hostplants (e.g. Munguira and Thomas, 1992;Valtonen et al, 2006b).…”