… that blows nobody any good” is an old English idiom that suggests that most bad things that happen have a good result for someone, somewhere. And Markus Hauck and colleagues in Göttingen, Germany, have illustrated this nicely – and rather literally – with some work looking at lichens growing in forests in Germany. In the days before global warming hit the headlines, “acid rain” was the big environmental concern in Europe, with westerly winds from the Atlantic picking up polluted air from industrialised regions (of the UK in particular) and blowing it up across Scandinavia and northern Germany, where it would be washed out in rainfall. This was a time when the UK was fuelled by coal, and that coal contained a lot of sulphur – so the smoke was heavy in sulphur dioxide, which dissolved in the clouds to produce the aforementioned “acid rain”. From the early 1980s onwards, there was widespread concern that large areas of forests in northern Europe were being damaged and public concern led to legislation to reduce pollution. The result has been that over the last 20 years sulphur dioxide emissions have fallen back to levels not seen since the early days of industrialisation in the 19th century. But what Markus Hauck and his team have found is that one of Europe’s most common lichens, Lecanora conizaeoides, actually quite liked this “ill wind”, as it thrives in acidic conditions. Their study in the Harz Mountains of northern Germany shows that the lichen has undergone a dramatic decrease in abundance within only 15 years, from being the most dominant species of its type to a point where it can now be described as rare. Their analysis suggests that this is attributable to just a very slight decrease in the acidity of the bark on the trees on which the lichen lives, a change of only 0.4 pH units. To put that into context, that is about half the difference in acidity that you would find between a glass of orange juice and one of tomato juice. So for this lichen at least, a fair wind is not as welcome as an ill one. Full details of the work can be found in the August issue of Annals of Botany.
Lecanora conizaeoides is an epiphytic lichen adapted to very acidic conditions, and a reduction in atmospheric SO2 in western and central Europe has coincided with a dramatic decline in its distribution. Hauck et al. study lichen diversity and bark chemistry in northern Germany and compare the results with comparable data collected 13–15 years previously. Neither competitors nor parasites that might have benefitted from the reduction in SO2 are likely to account for the decline in L. conizaeoides cover on trees, and the results instead suggest that an increase of only 0.4 in bark pH is responsible.