Retention forestry can maintain epiphytic lichens on living pine trees, but provides impoverished habitat for deadwood-associated lichens

Managing forests for timber yields reduces the amounts of old trees and
deadwood, which has profound effects on species that are dependent on
them. Retention forestry, where some trees are permanently left
unharvested on clearcut sites, may enable the formation of deadwood and
old trees in managed forests, but it is unresolved how well these
practices facilitate the occurrence of species in managed forests,
especially in the long term. We studied the capacity of tree
retention practices to support the diversity of epiphytic lichens, a key
group among threatened forest species. We compared lichen assemblages on
retained trees in harvested sites to those on trees in unharvested control
sites. The data was collected 21 years post-harvest and included living
trees, snags (standing dead trees), and logs (fallen trees) of Pinus
sylvestris (Scots pine). Living trees, snags, and logs each hosted
distinct lichen communities. The highest lichen diversity was found on
snags. On living trees, species richness was similar in harvested and
unharvested sites, but there was slight species turnover. In contrast,
deadwood in unharvested sites hosted higher species richness and distinct
species assemblages compared to deadwood in harvested sites. These
differences were most pronounced on snags. Specifically, unharvested sites
contained high-longevity snags (kelo trees), which hosted unique lichen
communities with higher lichen richness than any other studied substrate,
including the highest numbers of red-listed and deadwood-dependent
species. Synthesis and applications: Retention forestry can support lichen
assemblages associated with living Pinus sylvestris. However, maintaining
deadwood-associated lichen diversity through retention practices entails
significant challenges. Deadwood-associated lichen diversity relies on
high-longevity snags and is not sustained by the habitats provided in
retention forestry. Biodiversity maintenance in forest management requires
comprehensive provision of the habitat features of unmanaged forests, such
as a qualitatively representative deadwood profile, which can prove
difficult.