Statistical analysis of the lichen vegetation of an avenue in freiburg (South-West Germany), with regard to injurious anthropogenous influences

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Abstract
The epiphytic lichen vegetation [Buellia punctata, Candelariella xanthostigma, Evernia prunastri, Hypogymnia physodes, Lecanora chlarotera, L. conizaeoides, L. hageni, L. subfuscata, Lepraria aeruginosa, Parmelia acetabulum, P. caperata, P. exasperatula, P. elegantula, P. fuliginosa, P. saxatilis, P. scortea, P. subrudecta, P. sulcata, Physica ascendens, Pseudevernia furfuracea, Xanthoria candelaria, X. parietina; mosses include Frullania dilatata, Hypnum cupressiforme and Orthodicranum montanum] on maple trees is described along an 1.1 km avenue leading from the outer suburbs of Freiburg toward center city. A special aim of this investigation was to examine the variation in the coverage by lichens altogether and by each lichen species as a function of increasing distance from the city. It required very accurate quantitative recording methods, including the method of hits and other statistical techniques. The coverage both of total trunk surface and of sectors facing different directions increases with increasing distance from the city. The distribution pattern of SO2 pollution in winter, especially under certain weather conditions, e.g., during winter highs with very high SO2 concentrations, implies a negative correlation between the amount of SO2 pollution and the total percentage of lichen cover. An influence of factors specific to urban climate and traffic emissions is neglegible. The stress caused by increasing immission from outer suburbs towards the city is also indicated by the decline in coverage by the lichens of foliaceous growth form, the increase in coverage by green algae and the lichens of crustaceous growth form, especially by the resistant Lecanora conizaeoides. The degree of lichen cover changes with exposure. The differences between the 4 exposure zones may be caused by climatic differences.