Global warming and alternative causes of decline in arctic-alpine and boreal-montane lichens in North-Western Central Europe.

Lichens are thought to be sensitive indicators of global warming, as the spread of several thermophilous epiphytes in north-western Central Europe has been attributed to late 20th century warming. In the present paper, the potential contribution of late 20th century warming to the decline of arctic-alpine and boreal-montane lichen species is analyzed. Relevant ecological groups of lichens include terricolous heathland species, saxicolous species of exposed rock outcrops and boulder fields as well as epiphytes of mountain forests. These three groups of lichens experienced significant declines before the onset of late 20th century warming in the 1970s. These declines can be attributed to the abandonment of traditional land use systems in the case of the heathland lichens, increased recreational use of the exposed summits usually inhabited by cold-tolerant saxicolous lichens, and to high atmospheric SO2 levels in the mid-20th century, but are probably not directly connected to global warming. [ABSTRACT FROM AUTHOR]