The efficiency of retention measures in continuous-cover forestry for conserving epiphytic cryptogams: A case study on Abies alba

Lacking structural diversity in production forests has been evidenced to decrease epiphytic bryophytes and li-chens. One approach to create structurally more diverse forests is retention forestry. Only a small number of studies focused on the effectiveness of retention measures in continuous-cover forestry. Most studies have been conducted in even-aged, clear-cut based management systems and applied different approaches, but they all have in common that the retained trees have been examined for epiphytes only after harvest. Thus, it remains unclear whether these trees or even a certain tree species could take the life-boat function for epiphytes on logged sites. Thus, prior to logging, we assessed epiphytic bryophytes and lichens on potential large living retention trees, here referred to as habitat trees (HT), of Abies alba and compared the diversity pattern to nearby average trees (AT; A. alba, Fagus sylvatica or Picea abies) of smaller sizes in selectively harvested continuous-cover forests. Selection of AT was based on the average stem diameter of all trees within the stand. We found that species richness and Simpson diversity of lichens were significantly higher on HT. For bryophytes, F. sylvatica AT showed significantly higher Simpson diversity. Mixed models revealed positive effects of F. sylvatica on bryophytes, whereas large stem diameters and elevation were the driving forces for lichens. Additionally, ordinations revealed clear patterns in species composition separating between conifers and broadleaved trees, and along increasing altitude and stem diameter. Concerning HT selection, we suggest to focus rather on the tree species diversity than on stem diameter, when aiming to protect epiphytic bryophytes and lichens.

Automated summary

Retention forestry is an effective method to create structurally more diverse forests, which can have a positive impact on epiphytic bryophytes and lichens. In continuous-cover forests, retained trees, especially habitat trees, have shown to support higher species richness and diversity of lichens. Species diversity of tree species may play a more important role in protecting epiphytic bryophytes and lichens than stem diameter.