The epiphytic moss species Orthotrichum rogeri is endemic for Europe, therefore listed in Appendix II of the FFH directive. The species can be found in several regions of Europe, but is rare or very rare in all localities. In Southern Black Forest, O. rogeri has one of its centres of distribution, its ecology and phytosociology was studied there. Based on systematic mapping of 150 occurrences of that species and related site descriptions, conclusions were drawn about several site characteristics. Investigated parameters were topographical localisation in the landscape, exposure of microsites, position of the moss colonies on the carrier tree, and species and d.b.h. (Diameter at breast height) of the carrier trees. For 62 trees the pH-value of the bark was measured, and for 66 occurrences phytosociological releves were recorded. Based on that, the phytosociology of O. rogeri was analysed. With respect to the site, it appears that cold air drainage and therefore cool nights are essential for the occurrence of that moss species.
