Biological indication of air pollution by lichen mapping in long time observation areas in Hesse/Germany

The longevity and sensitivity of epiphytic lichens to air pollution make th em useful instruments for ecological studies. On the basis of these conside rations, in Hesse six long time observation areas for lichens were installe d. It is the aim of these investigations to pursue the longterm development of air pollution by the aid of biological indicators. Lichen mapping was c arried out at hessian observation areas in 1992 and 1997. The investigation s occurred after the standardized mapping guideline of the German Engineers Association (VDI 3799, 1). At 114 investigation stations the changes of the lichen vegetation on 10 fr eestanding deciduous trees per station were examined. As essential results, the following statements can be made: At all observation areas the air pollution indices are in 1997 higher than in 1992, this means that air quality has become better in all examined area s. The increase of air pollution indices is high especially in such areas wher e they were low in 1992. On the other hand, the least improvements occur at those regions where the situation for lichen growth was relatively favorab le in 1992 already. The result is a leveling of the spatial differences in the air pollution situation in Hesse between 1992 and 1997. In all examined areas an increase of the number of lichen species can be re cognized between 1992 and 1997. Some of the recolonizers are sensitive to a ir pollution, others are indicators for eutrophication. The drop of acidophytic and the return of subneutrophytic lichens indicate a reduction of acid air pollutants.