Ecosystem service provision by road verges, Phillips et al. 2019

‘Road verges’ are strips of land on either side of roads and highways that are on average 3-4m wide, but can be as narrow as a few centimeters or many meters wide. “Road verges are commonly grassland habitats, but can be shrubland, forest or artificial arrangements of trees and horticultural plants, and we use the term also to include bare earth and freshwater bodies (e.g. ditches)” [Phillips 2019: 489]. They can also be barren ground or ditch. Not all road verges are managed; when management does occur, it is typically geared toward safety – clearing vegetation to enhance visibility.

There is currently an estimated 36 million linear kilometers of road network in the world, the length of which is expected to increase by 70% by 2050; thus, the total area of road verges will increase as well. “Road and road verge construction will displace habitats and cause many negative ecological and social impacts” [Phillips 2019: 494]. However, there is potential to mitigate that impact by maximizing the ecological value of road verges. Currently, “there may well be 270,000 km2 of road verge globally (0.2% of land), which is similar to the total area of the United Kingdom” [Phillips 2019: 492], with this surface area expected to grow.

While roads run like a network of veins across landscapes, causing widespread negative ecological impacts to adjacent areas, road verges form a parallel network and have the potential both partially to mitigate negative impacts of roads and to deliver environmental benefits [Phillips 2019: 490].

Where roads cut through natural habitat, the road verges will represent a net loss of biodiversity. By contrast, verges can increase biodiversity in highly degraded environments such as cities or industrial farmland. Furthermore, because of the growing urban population, the importance of natural and semi-natural environments will be increasingly important. Road verges designed to maximize ecological value thus have an important role to play in the health and wellbeing of urban residents.

Road verges might increase connectivity in highly modified urban and agricultural landscapes if road verges of suitable size, habitat quality and continuity are created alongside roads, at least for species that are highly mobile or able to persist in narrow, linear habitats [Phillips 2019: 495].

While roads often act as barriers to wildlife and ecological connectivity, ecological corridor design could benefit by taking into account the potential benefits of road verges.

If road verges were integrated into such [ecological corridor design] projects, they might play an important future role in increasing connectivity between natural and semi-natural habitats, particularly across otherwise habitat-poor, human-dominated landscapes where roads often occur [Phillips 2019: 495].