Changes in urban lichen diversity after a fall in sulphur dioxide levels in the city of Tampere, SW Finland

Abstract

As a consequence of air pollution, lichens disappeared from the central part of the city of Tampere. A lichen desert of 5 km covered the centre in the beginning of the 1970s. Later the mean annual SO2 concentration decreased from 160 μg m in 1973 to 2 μg m in 1999. The monitoring of lichens on the trunks of Tilia x vulgaris which began in 1980 showed that recolonisation had started slowly but advanced rapidly after 1985. In 2000, the numbers of species in the monitoring sites were over 10 times and cover values nearly 200 times higher than in 1980. The number of species increased linearly, while cover values rose exponentially. In 2000, the reference sites had twice as many lichen species and over three times higher cover than the city sites. Thus, the recovery of the lichen flora and vegetation will take several decades after the virtual elimination of SO2.