Air as pure as wine?
Most people are aware that lichens do not grow well where there is air pollution. They are like the canary down the coal mine - detecting air pollution at lower levels than many other organisms. In 1972 school children throughout Britain mapped lichens around their homes which helped produce the 'Mucky air map of Britain'. It revealed that the largest reservoirs of pure air are in Scotland, which, apart from Scotland's Midland Valley, appears to enjoy air as pure as wine. This is not quite the full story however.
The school children's map reflected the distribution of sulphur dioxide to which virtually all lichens are sensitive. However there are several different types of air pollution. Despite a big drop in sulphur dioxide levels, acid rain which travels a lot further, is still affecting certain woodland lichens - for instance along the southern edge of the Highlands and the remoter areas of the Cowal peninsula. In addition, residents in the Cairngorms have reported up to five centimetres of highly-acidic, black snow falling several times a year. When it melts this produces a pulse of toxic water, but its effect on lichens is not known. A further cause of concern is increasing long-distance nitrogen pollution from sources associated with industry, transport and agriculture.
This goes to show that we must not be complacent about air pollution effects on Scottish lichens and assume that remoteness from sources will always protect them. But for the time being, areas north of the Highland Boundary Fault enjoy some of the cleanest air in Europe.