THE IMPACT OF A ROAD UPON ADJACENT HEATHLAND VEGETATION - EFFECTS ON PLANT-SPECIES COMPOSITION

1. The effect of a road upon heathland vegetation was investigated at five sites adjacent to the main trunk road through the New Forest, Ham pshire, UK, with nine supplementary sites adjacent to five minor roads . 2. There was enhanced growth of vascular plants, notably heather and grass species near the road, which was probably due to oxides of nitr ogen from vehicle exhausts. There was a decrease in the abundance and health of lichens near the road. 3. There was an increase in the abund ance of grasses in the heathland near roads, which may be due to the c hanges in relative competitive ability of plant species under conditio ns of eutrophication. 4. The extent of the edge effect in the heath wa s closely correlated with the amount of traffic carried by the road, w ith a maximum edge effect of 200 m adjacent to a dual carriageway. Thi s should be taken into account when considering the environmental impa ct of new roads. Road widening with its associated increase in traffic can also be expected to impact on existing oligotrophic communities b eyond the actual land-take. Such schemes should include buffer zones t o protect oligotrophic communities or other measures to minimize the p ollution input from vehicle exhausts to environmentally sensitive area s.