Ecological impacts of air pollution from road transport on local vegetation

Motor vehicles emit a cocktail of pollutants and are a major contributor to ground-level air pollution, but little is known regarding the ecological impacts of air pollution from roads on the surrounding vegetation. Data are presented on vegetation at three sites adjacent to two major motorways in the UK, comprising two woodland sites and one blanket bog site. Surveys of oak and beech tree health (at the woodland sites) and species composition (at the blanket bog site) were undertaken along transects away from the motorway.The oak tree health survey found increased defoliation and insect damage near to the motorway, and the beech tree health survey also found poorer crown condition close to the motorway. Vascular species composition showed a trend towards species adapted to higher N availability close to the motorway, while the moss Polytrichum commune showed a significant decline in frequency with distance from the motorway. The effect of the road was estimated to extend to approximately 100 m at these three sites; this distance was consistent with the measured profile of NO2, which declined to background levels at about 100 m. The results suggest that emissions of air pollutants can have significant ecological impacts on sensitive sites within 100 m of major roads.