Community dynamics of lignicolous lichens on standing deadwood in a 275‐year chronosequence

Dead trees provide discrete habitat patches in which patch quality changes gradually due to wood decomposition. Although in most cases these patches persist for not more than a few decades, in some ecosystems deadwood decomposition and the consequent change in habitat patch quality can be a centuries‐long process, potentially leading to dynamics of deadwood‐associated communities taking place over a similar time scale. We studied the dynamics of lignicolous lichen communities on snags in near‐natural European boreal forests. We surveyed lichens on 331 Pinus sylvestris snags and obtained their year of death with dendrochronological methods. The snags comprised a chronosequence of 275 years in time since tree death. Most lichen species (86%) displayed an association with either fresh, intermediate or long‐standing snags, with only few species occurring at a similar rate throughout the chronosequence. Thus, the habitat patches provided by snags were indicated to be characterized by a sequence of colonizations by and extinctions of lichen species with differing niches. Accordingly, community composition was closely connected to time since tree death. Associations with long‐standing snags were most frequent (46% of species), and consequently, species richness increased with time since tree death – approximately a 2.5‐fold increase from 20 to 90 years from death – but increased no further beyond 90 years since death. Several obligate lignicoles occurred only on long‐standing snags indicating their dependence on this specific type of deadwood. Our findings show that time since tree death is a primary determinant of the species composition and richness of lignicolous lichens on snags. Thus, lignicolous lichen communities are intrinsically linked with snag dynamics that occur over centennial time scales in boreal forests. Lignicolous lichen diversity is dependent on long‐persisting standing deadwood that typically occurs only in natural forests.