Forest history and epiphytic lichens: Testing indicators for assessing forest autochthony in Switzerland

Epiphytic lichens are widely used to indicate old undisturbed forest stands with a long forest history that are of outstanding interest for biodiversity conservation. Swiss forest stands without any significant human impact like clear-cut or afforestation that have natural tree species composition and a continuous forest cover during the last 120 years are considered to be autochthonous. In this study nationwide indicators of forest autochthony were developed using the Swiss National Forest Inventory data on forest structure, forest history and forest management from about 6500 sample plots across the country. We selected a set of epiphytic lichen taxa (n = 19) that due to their low dispersal range or specific substrate requirements are mostly restricted to old-growth forests and are easy to recognize in the field by forest practitioners. The indicator species analysis was performed separately for Swiss mountain (n = 3510) and lowland forests (n = 2952). Overall, the number of indicator lichens was higher in autochthonous forests and varied significantly with biogeographical region. Forest autochthony had a significant impact on the occurrences of indicator lichens at high altitudes but not in lowland forests. This effect was probably due to habitat and substrate preferences of some indicator lichens and also the fact that Swiss mountain forests were less affected by forest management. The fruticose species, i.e. Bryoria sp., Evernia divaricata, Letharia vulpina, Usnea sp., pin lichens as well as Chrysothrix candelaris, Cetrelia olivetorum and Lobaria pulmonaria were found to be reliable indicators of forest autochthony in Swiss mountain landscapes. However, these species were not exclusively present in autochthonous forest habitats, which is why the co-occurrence of several different indicator lichens should be considered to adequately indicate autochthonous forest stands. In Swiss lowlands we did not reveal the association of indicator lichens tested to autochthonous forest stands and thus further research is needed to select an effective set of lichen indicators for such lowland forests. Our results are, however, valuable for the development of a national monitoring program to detect autochthonous forest stands that are target areas for biodiversity conservation.