The current state of the lichen flora in the summer of 2023 in the Rohrach Nature Forest Reserve (Vorarlberg, Austria) is presented. The results are compared with the lichen survey from 1996. In 1996, 118 lichen species were recorded in the study area, whereas in 2023, only 14 species remain. This represents a complete decline of the lichen population in the Rohrach Nature Forest Reserve. Using the bioindicator »lichen«, both the level of pollution in the study area due to air contamination and the degree of naturalness of the forest stand are assessed: The extremely low abundance of the recorded lichen species, the small cover of individual species on the host trees, and the absence of entire groups of species suggest that the Nature Forest Reserve is subjected to a permanent and strong impact of pollutants. Due to the high proportion of lignicol lichens in the total species count, the degree of naturalness of the forest stand is classified as high. Keywords: biodiversity, biomonitoring, lichens, bioindication, air pollution, lichen species decline.