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Felling of old trees as well as changes in land use and management of wooded pastures has led to the decline of biodiversity associated with old deciduous trees in Europe. This also applies to Sweden’s most species rich tree, the oak tree (Quercus robur), which changes with age and develops, for example, a rougher bark structure, deeper bark fissures and cavities. These give rise to several different microhabitats that favor the presence of lichens, mosses and wood-dependent organisms. To preserve the biodiversity, environmental conditions linked to a high diversity need to be identified and described, of which indicator species are a simplified way of measuring diversity. Epiphytic lichens are well-used indicators of environmental conditions because of their habitat specificity, longevity and sensitivity to air quality and humidity. In this study, the impact of regional (latitude, longitude and dominated landscape) and local (diameter and sun exposure) environmental variables on species richness and occurrence of epiphytic lichens on coarse oak trees (Quercus robur) were analyzed in meadows and pastures in southern Sweden with generalized linear models (GLM). A total number of 2346 oak trees were included in the study, of which about 47 % had presence of at least one of the studied lichen species. All environmental variables demonstrated significant effects on species richness, of which the regional had the greatest effect. Also with the species-specific analyses the same effect of the regional variables was found, while single species showed different requirements for the local factors. The results indicate that global warming may move the Swedish species composition more to the Northeast and that increased homogenization of the landscape may threaten the diversity attached to oaks. The results also demonstrate the importance of preserving a varied landscape with trees of different sizes, ages and different levels of sun exposure to accommodate a greater diversity of epiphytic species, but also other species linked to oak trees. |
