On 132 long-term ecological observation plots in the Swiss Central Plateau and the Pre-Alps the epiphytic lichen flora of 849 trees was surveyed by standard sampling. The lichen data of all tree species in forest and non-forest areas were analysed in order to provide simple, reproducable and comparable characteristics for long-term observation. For the 10 most common tree species in forest and non-forest areas the mean number of lichen species, the mean cover of lichens and bryophytes, as well as the mean indicator values for light, reaction and toxitolerance (Wirth 1992) were determined. Based on the data of Picea abies in forest, arranged in groups according to the 4 vegetation belts and 5 dbh-classes, the mean values and their confidence intervals were calculated for qualitative and quantitative (cover) data. For the detection of environmental changes, ordinal weightening of cover-estimates is proposed, considering effort, reproducibility and accuracy of sampling and calculation. As the indicator values are ordinal scaled from 1 to 9, and their distribution on the scale is not symmetric, the calculation of their mean values is not unproblematic. The effect of the latter was estimated by comparison with calculations based on a scale from 1 to 5 with a symmetric distribution of all indicator values. Finally, for the 5 most abundant tree species in forest and non-forest areas, the estimates and their confidence intervals of each of five indicator-classes were calculated. If sample size is big enough, estimates of indicator-classes, especially for toxitolerance, are proposed for ecological long-term characterisation. The ecological indicator values of Wirth (1992) have shown to be an appropriate tool for long-term observation. In this study 79% of the most abundant species are characterized by indicator values. 12 trees were without any indicator-lichen, only 2 more than with no lichens at all.