The Indicator Value of a Set of Lichen Species Assessed with the Help of Log-Linear Models

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Abstract
The value of 19 epiphytic lichen species as air pollution indicators was tested in the Khamar-Daban mountain range in east Siberia. Frequency of occurrence of a species was used as the indicator characteristic. Altitude and distance from the pollution source were considered as environmental factors. The methodology of fitting log-linear models to contingency tables with presence/absence (frequency) scale as an additional dimension is presented. The significance of changes in species frequency is studied by examining the significance of the model parameters, which account for interactions of the environmental factors with the ‘frequency factor’. Only two species, Parmelia caperata and P. olivacea, were found to be good pollution indicators in that they showed a uniform monotonic (unidirectional) response to the factor of distance at all altitudes. The frequency of 12 species changed significantly and monotonically with distance in one or two altitudinal zones.