Effects of stand-level disturbances on the spatial distribution of a lichen indicator

Due to its assumed dispersal limitation and susceptibility to disturbance, the epiphytic lichen Lobaria pulmonaria is used as an indicator of undisturbed forest stands. The hypothesis was tested that stand-level disturbances have a long-lasting negative impact on the occurrence of L. pulmonaria. Two 19th century stand-level disturbances were reconstructed Using aerial photographs from 1933. For 7769 potential host trees within a random sample of 251 plots of I ha, the presence of L. pulmonaria, tree species, and diameter at breast height were recorded. An analysis of variance showed that neither historical stand-level disturbances nor current grazing reduced the proportion of colonized trees. Spatial analysis at the tree level revealed, a patchy distribution of colonized trees, suggesting L. pulmonaria colonization from nearby sources. Spatial analysis at plot level even showed a positive spatial association of L. pulmonaria with historic disturbances. We conclude that the presence of L. pulmonaria may provide information about conservation value of a landscape, but not necessarily at a forest stand scale. Although indicator species, such as L. pulmonaria, may be an efficient means to assess the conservation value of a forest, spatially and temporally explicit knowledge of the species' life history characteristics is indispensable in order to prevent possible misinterpretation of ecological processes that the indicator aims to unravel.