Butterfly colonisation of a new chalkland road cutting

Abstract

Abstract The design of new roads has the potential to provide new habitats and increase biodiversity value. The cutting and verges of the Weymouth Relief Road, Dorset, completed in 2011, replicate low‐fertility chalk grassland in an area previously occupied by arable farmland and improved grassland. We examine the results of post‐construction butterfly surveys carried out in 2012–2020 to test whether butterfly abundance, species richness and species diversity increased in the post‐construction period. Analysis is also undertaken of the factors affecting the colonisation of the verges by butterfly populations. Butterfly abundance increased in the post‐construction period when assessed by two methods: mean counts per survey visit and maximum counts. Species richness also increased, but no significant trends were observed with respect to species diversity. The 30 butterfly species recorded on the verges represent 51% of Britain's resident or regularly occurring migrant species and include habitat‐restricted chalkland species. The most significant factor affecting speed of colonisation of the cutting and verges was an index of local presence, defined as the number of 1 km squares where two or more individuals of a species had been recorded prior to road construction in a 10 km square centred on the site. The separation distance between the site and the nearest butterfly population did not significantly affect the speed of colonisation. Our results validate the low‐fertility approach to road verge establishment and management. The experience of the Weymouth Relief Road is influencing future road verge construction and management in the United Kingdom.