Living and dead retention tree value in the conservation of bryophyte and lichen communities in production forests

Retention forestry has become increasingly popular in recent decades. Although retained trees have a high postharvest mortality rate, little is known about the role of dead retention trees in the conservation of lichen and bryophyte species. In this study, species composition and richness of bryophytes and lichens on living trees, and snags and logs of dead retention trees was assessed in 20 young stands in Latvia. The goal was to compare how the species richness and composition differ between retention tree structure types (living trees, snags, and logs). The results showed that higher bryophyte and lichen species richness per tree was found on logs and snags compared to living trees. Species composition significantly differed between retention tree structure types. Snags and logs hosted a higher number of woodland key habitat species than living trees. Retention tree species had a significant effect on bryophyte species richness on living trees, while tree species and diameter at breast height were important for bryophyte diversity on snags, and stage of decay on logs. In contrast, the number of lichen species on snags and logs was affected only by retention tree species while none of these factors had a significant effect on lichen species on living trees. As a conclusion, the conservation of bryophyte and lichen diversity on retention trees needs to consider also their role as deadwood substrates after their death.