Tree species choice by forest management and biodiversity: Replacing Abies alba by Picea abies and Pseudotsuga menziesii drives epiphytes to higher elevations

Pseudotsuga menziesii is considered as a replacement tree species for the drought-sensitive Picea abies in Central European forests, which was often cultivated outside its natural elevational distribution range. Hence, the natural tree species composition at lower elevations was replaced mostly by Picea abies , which in turn is partly displaced by Pseudotsuga menziesii . How epiphytic bryophytes and lichens respond to such alterations of the natural tree species composition has been only insufficiently studied so far. Hence, we compared taxonomic and functional diversity patterns of epiphytes between each 48 tree individuals of Picea abies and Pseudotsuga menziesii with native Abies alba along an elevation gradient in temperate mountain forests of southwest Germany. Lichen α- and γ-diversity was significantly higher on Abies alba , whereas no difference was found for bryophytes. Our models indicated that stem diameter and elevation as well as Abies alba , contrary to Picea abies and Pseudotsuga menziesii , favoured lichen richness. Again, no impact on bryophyte richness was detectable. Trait-based analysis revealed that Pseudotsuga menziesii was preferred by acidophytes. Especially lichen species with the secondary metabolite fumarprotocetraric acid were apparently able to colonize the highly acidic bark. Contrary to this, lichens with parietin and usnic acid avoided Douglas fir and were rather associated with Picea abies and Abies alba , which was also strongly preferred by liverworts and obligate epiphytic bryophytes. Threshold indicator taxa analysis identified epiphyte communities already increasing in abundance at ∼750 m a.s.l. on Abies alba , but only at ∼950 m a.s.l. on Picea abies and Pseudotsuga menziesii . Abies alba turned out to be a very valuable tree species for epiphytic bryophytes and lichens compared to non-native Pseudotsuga menziesii and Picea abies , when cultivated outside its natural range. At lower elevations, epiphytes do not seem to have the capability to adapt to Douglas fir and spruce under the present climate, but only at higher elevations under further increased humidity levels. This suggests that the anthropogenic change in tree species composition pushed epiphytes of the natural forest vegetation towards higher elevations. • Abies alba favours epiphytic bryophytes and lichens • Acidophytic bryophytes and lichens are associated with Pseudotsuga menziesii • Obligate epiphytes were rather associated with Abies alba and Picea abies