Effects of roads on adjacent plant community composition and ecosystem function: An example from three calcareous ecosystems

Roads and exhaust emissions can affect plant communities directly, for example via direct foliar uptake of exhaust products, or indirectly via changes to soil biogeochemistry and hydrology. A transect study adjacent to roads of different traffic densities was carried out at three species-rich calcareous grasslands in south eastern England. Measured annual NO2 concentrations and modelled NH3 concentrations increased towards the roads and with higher traffic densities, and there was evidence of increased soil moisture, pH and heavy metal concentrations at roadsides. Increases in the abundance of nitrogen (N) tolerant species and grasses at roadsides were associated with N enrichment from vehicle exhausts at two of the sites. In contrast plant species richness, the abundance of forb and moss species declined at roadside locations. As vehicle usage spreads across the world, it is increasingly important to understand the effects of road traffic on adjacent ecosystems to inform traffic and conservation management policies. - Highlights: ► A transect study assessed the effects of roads at three calcareous grasslands. ► Substantial areas experienced NOx above the critical level of 30 μg m−3. ► Copper, zinc and lead concentrations approximately doubled in roadside soils. ► Roads may also disrupt natural drainage and increase the pH of soils. ► Plant compositional changes were found in relation to roadside proximity. - Roads are responsible for a suite of environmental perturbations which are associated with changes in plant composition, species richness and ecosystem functioning.