Tree species identity modifies the efficiency of habitat tree retention for conserving epiphytes in temperate mountain forests

Abstract

Forest ecosystems play an outstanding role in supporting diverse bryophyte and lichen communities. However, intensive forest management has led to a considerable decline of epiphyte communities, which are sensitive to the simplification of forest stands and the interruption of stand continuity. Retention forestry, which originally aimed to conserve important structural elements for biodiversity after clearcut, has more recently also been incorporated into continuous-cover forestry in temperate European forests. As both management systems differ from each other, it is difficult to transfer findings to the efficiency of retention measures for biodiversity conservation from clearcut to continuous-cover management systems. Therefore, we studied how habitat trees retained in continuous-cover forestry in temperate mountain forests of Germany dominated by Fagus sylvatica, Picea abies, and Abies alba would benefit epiphytic bryophytes and lichens. We analysed the epiphyte vegetation on 1254 trees in 132 forest stands. We compared large-sized habitat retention trees (HT) and smaller-sized average trees (AT). We detected a significantly higher species richness on HT, which was more strongly driven by lichens than by bryophytes. Even stronger increases in Simpson and Shannon diversity suggested that these increases in richness were due to increased population sizes of several species and not due to the addition of few individuals of few species. Strong variability in the response of epiphyte diversity occurred between tree species, with bryophytes being particularly favored by F. sylvatica and lichens by A. alba. Retention of HT is thus a suitable tool to conserve epiphytes in Central European temperate forests, even after blind selection of HT without consideration of the epiphyte vegetation before tree selection.