Long distance nitrogen air pollution effects on lichens in Europe

The epiphytic lichen flora of 25 European ICP-IM monitoring sites, all situated in areas remote from air pollution sources, was statistically related to measured levels of SO2 in air, NH4+, NO3- and SO42- in precipitation, annual bulk precipitation, and annual average temperature. Significant regression models were calculated for eleven acidophytic species. Several species show a strong negative correlation with nitrogen compounds. At concentrations as low as 0.3 mg N l(-1) in precipitation, a decrease of the probability of occurrence is observed for Bryoria capillaris, B. fuscescens, Cetraria pinastri, Imshaugia aleurites and Usnea hirta. The observed pattern of correlations strongly suggests a key role of NH4+ in determining the species occurrence, but an additional role of NO3- cannot be ruled out. Some species show a distinct response to current levels of SO2 as well. It may be concluded that long distance nitrogen air pollution has strong influence on the occurrence of acidophytic lichen species. (C) 2003 The British Lichen Society. Published by Elsevier Ltd. All rights reserved.