Promoting a wide variety of species and plant-life – biodiversity – is a priority for conservationists, especially in order to protect species that are threatened by habitat loss, pollution and climate changes, pollution. Road verges can be remnants of original habitat or created as new habitats in the urban environment. They are linear habitats which can connect other larger areas of habitat as part of ecological networks. How they are managed can have a big impact on the diversity of plants, invertebrates and other wildlife that they can support.
The Sheffield Living Highways project was a collaborative project involving Sheffield and Rotherham Wildlife Trust, the University of Sheffield, Sheffield City Council and Amey 2015-2019. Its aim was to trial whether changes to the management of the city’s grass verges can have a positive impact on the city’s ecosystems.
Amey is responsible for the maintenance of 2.9 million metres2 of road side verges in Sheffield as part of the ‘Streets Ahead’ contract. Most of these verges are areas of regularly mown grass, but they also include some rural verges, shrubs and small patches of green space. The ‘Streets Ahead’ contract is very specific about how these verges should be managed with a focus on the frequency of the mowing cycle and the height of the grass sward; however, over the last few years, The Sheffield Living Highways Project partners looked at whether changes to the way the verges are managed, such as leaving it to grow longer, replacing some grassed areas with wildflowers, and introducing native hedgerows or trees, could increase the biodiversity value of these habitats.
Results and lessons learnt
In 2016 and 2017 a mowing trial was conducted on 17 urban roads in Sheffield. On one side of each road, mowing proceeded as normal (every 3-4 weeks) but was reduced by half on the other side of the road (every 6-8 weeks) during the entire mowing season (April – October). Grass cuttings were left on grass verges after mowing took place. Plant and insect surveys were conducted by the University of Sheffield on these trial roads to measure the impact on biodiversity. Roads were a mix of residential streets and non-residential key transport links. The mowing trial was communicated to the public through a press release, signs on lamp posts and leaflets delivered to every house on the mowing trial roads. Research also examined the public perception of the mowing trial;
Results showed many local residents do not always like the appearance of unmown grass, meaning it is not always appropriate just to let grass grow longer directly outside people’s houses. However there was some appreciation that it is better for biodiversity.
This road verge was shown to support remnants of floristic diversity, but was being mown too frequently for the flowers to display.
A stretch is now subject to less frequent mowing and this has been successful in allow the herbs and grasses to flower. In 2019, yellow rattle seed was applied by SRWT to the central reservation to increase the floristic diversity further.
Shrewsbury Road/ South Street
Near the back entrance to the city’s main train station, was one of the first verges to benefit initially after the Living Highways project worked with the Sheffield 20s and 30s Walking Group to sow wildflower seeds on a verge in the area. The results were spectacular, with a host of poppies taking hold and transforming the character of the street. The Trust would like to thank the Walking Group who obtained the seed from GrowWild. The species composition is changing over time as annual species that were present in the first year are no longer flowering, but in 2019 the site still supported 35 herb species and 12 grass species.
A plot at the Capita Building near West Bar was seeded by Amey as part of the trial and again was a mass of colour in its early years and is now maturing as a site due to the seed mixed used. SRWT have been monitoring the botany of the site (2016-2020) and the site supports 31-40 species of herbs and 7-10 species of grasses. However, appropriate on-going management of the site is required.
A trial site near Tinsley roundabout which was close mown amenity grassland was seeded with yellow rattle and green hay from our Carbrook Ravine nature reserve as a trial. Volunteers collected the seeds from the yellow rattle seeds in July, before they set seed and dried them out until autumn when they were sown, along with the hay cut that day from the reserve (known as green hay) to spread on the site which was frequently mown amenity grassland. Yellow rattle is a parasitic plant which reduces the vigour of dominant grasses, allowing other species to flourish. The trial has been encouraging and has reduced the frequency of mowing needed at this site, although on-going appropriate management is needed. The site was monitored by Trust volunteers and supports a greater diversity of plant species with a maximum count of 2 herb and 10 grass species recorded.
Challenges and lessons learnt
Literature review recommendations such as mosaic mowing were not implemented as the Streets Ahead contract states that grass must have a uniform appearance. Also increased operational costs as not very efficient.
Also recommended were twice-yearly cut and collect –but Streets Ahead said that in most cases it was too costly and arisings potentially too contaminated – not enough arisings from urban verges for anaerobic digestion.
The soil fertility of sites/verges is key to what will grow if mowing is reduced and/or seed mixes are introduced. Soil testing was very informative– most verges sampled had a high phosphate index (>2) – too fertile/productive to support a high biodiversity sward.
Grassland management is complicated – each verge can be different. Need to have the involvement of people who understand grassland ecology. However, contractors prefer simple changes.
On-going management is important – especially with changing staff.
Top up seeding can be helpful.
If seeding – choosing or designing native, perennial seed mix is optimum – although there can be issues with supply chains of contractors.
Public perception studies – when implementing management changes, undertake public engagement and show some element of care for greater acceptance.
Although making changes can save £ and increase biodiversity over time, initial investment of £ and staff time and willingness to implement change is needed.
Reduced mowing in some urban areas
In 2018, Amey (outside of the partnership project) implemented plans to conduct one annual grass cut in late summer on 20% of the urban road verge network. This resulted in swathes of dandelions flowering and setting seed in addition to localised displays of cowslips, cuckoo flower and cats-ear during the spring. However, the visual appeal and diversity of the majority of verges reduced during the summer as a result of the fertility and productivity of the majority of sites, leading to some complaints to Streets Ahead. The results of this ‘one cut a year’ approach suggest that high soil fertility will limit the capacity of many urban verges to support biodiverse swards and that at least one additional cut may be required for wide-ranging public acceptance. The experience of 2018 also confirms the earlier research that public education is critical to the long-term success of altered road verge management in a city context. Therefore, the final consideration when selecting verges is the level and costs of public relations work that would need to be undertaken.
- If you want to contact us about road side verges you can email us via email@example.com or share your pictures on Twitter or Facebook using the #livinghighways hashtag.
- In September 2019 we helped to organise a national Road Verge Management Symposium with partners Butterfly Conservation and Natural England, the proceedings of which can be found here.
- You can find out about other Wildlife Trust road verge projects here, where you can also download a Managing Grassland Road Verges Best Practice Guide.
- For information on our engagement with the ‘Streets Ahead’ project, see here.