Lichens and air pollution.

A study was made of the lichen vegetation of south-west Hampshire and, in particular, in the vicinity of the oil refinery at Fawley. The macrolichen vegetation of oak boles shewed a consistent pattern of deterioration in terms of the frequency and cover of individual species in relation to the urban areas of Poole-Bournemouth and Southampton and the oil refinery at Fawley. Differential species sensitivity/tolerance to air pollution was found. Sulphur dioxide is considered to be the primary causal factor of this deterioration, with other environmental factors modifying the response. In particular, varying land-use appears to account for irregularities in the pattern of deterioration. Acidification of the substrate upon which lichens grew was found in polluted areas and its influence is considered to be contributory to the direct influence of sulphur dioxide on lichen propagules and thalli. The use of lichens to estimate sulphur dioxide pollution is discussed. Their use to distinguish between relatively unpolluted ('clean'), becoming polluted and polluted conditions, using simple quantitative measurements involving the minimum of species identification, is advocated for non-professionals for primary surveys. The lichen vegetation of the south-eastern flank of the New Forest was found to be in a state of deterioration and is seriously threatened by the continued industrialization and urbanization of the western shores of Southampton Water.