The article deals with an overview of bioindication methods of air pollution used at Slovenian forest decline inventories, and more details with the bioindication of air pollution by epiphytic lichen vegetation. The results of epiphytic lichen vegetation assessment in forest die-back inventory carried out in 1991 are presented completely, and partly also the comparison of the results of the inventories carried out in 1993 and 1994. The inventory of forest decline in 1991 was carried out on a 4 x 4 km grid, while each years' inventories, e.g. those in 1993 and 1994 were limited only to a 16 x 16 km grid. The method of epiphytic lichen vegetation mapping in forest decline inventories is based on the assessment of cover and frequency of fructicose, foliose and crustose lichen thalli in a group of six of the most convenient trees for epiphytic lichen observation of the 24 trees included into forest decline inventory at a plot. On the basis of the assessment of the cover and frequency of all three lichens thalli types, the index of atmospheric purity was calculated for each assessed tree and together for the plot. Index values were determined separately for tree crowns, trunks at the breast height and for the base of the trunks. Index data are presented separately for observations on Norway spruce, common beech and hornbeam, silver fir and oaks and also compiled together regardless trees species on which lichens were observed. High values of index (0-54 for a whole tree, 0-18 for separate tree strata) indicate rich epiphytic lichen vegetation and clean air, low values indicate poor epiphytic lichen vegetation and presumably polluted air. Index values show that air pollution in Slovenian forest is rather high, especially in the vicinity of the major known air pollution sources but also in some areas without known local emissions of air pollutants. As expected, index values of atmospheric purity are the lowest when calculated for tree crowns, yet among the values calculated for tree species the common beech with hornbeam show the lowest data due to the type of crown and bark quality of these two tree species. This can indicate the influence of acid precipitation, not only in the surroundings of the sources of high sulphur dioxide pollution in central and north-east parts of Slovenia but also in higher elevations in west and south-west parts which are rich in rainfall but without major local emissions. The results obtained by this simple method of epiphytic lichen mapping proved lichens as good air pollution indicators also in forests. The method is suitable for large scale mapping where species mapping is not possible due to limited time and funds.
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