Road verge extent and habitat composition across Great Britain

Abstract

There is growing societal and scientific interest in enhancing road verges for nature and the environment. This is partly because they are estimated to cover large areas in some regions. Yet, to our knowledge, there has been no quantitative assessment of national road verge extent, or of the habitats they encompass. We present a novel method for characterising and classifying road verges remotely. We use this to evaluate the extent and habitat composition of road verges across Great Britain, and to identify opportunities for improving verges for nature and the environment. We use stratified random sampling of freely-available road maps combined with satellite (Google Earth) and ground-level imagery (Google Street View). Overall, we estimate that there are 2,579 km2 (2,149-3,010 km2) of road verges across Great Britain, equivalent to 1.2% of land area, of which 707 km2 (27.47%) is short, frequently-mown grassland, 1,062 km2 (40.87%) is regular grassland, 480 km2 (18.73%) is woodland, and 272 km2 (10.66%) is scrub. By comparison, we estimate that there are 3,694 km2 of hard road surfaces across Great Britain, equivalent to 1.8% of land. Only 27% of frequently-mown grassland verges contained trees, indicating potential for planting trees and shrubs to provide environmental benefits. Our findings suggest that there are significant opportunities to enhance (i) verges along major roads, because these constitute a disproportionately large area of road verge and have the widest verges, and (ii) frequently-mown grassland verges for example by, where appropriate, reducing mowing frequencies and/or planting trees. Our method can be used, adapted and further developed by others, for example to assess road verges across other regions, and to assess verge habitat composition in greater detail.