Effects of boreal ground layer shrubs and bryophytes on the diversity, biomass and composition of lichen communities across contrasting ecosystems

There has been much recent interest in understanding how abiotic factors such as light, nutrients, and soil moisture affect the composition and biomass of lichen communities. Meanwhile, whether and how ground layer vegetation such as bryophytes and shrubs also influence lichen communities have received much less attention, particularly regarding how these effects vary across environmental gradients. In this study, we used a long‐term (19‐year) biodiversity manipulation experiment to assess the importance of feather moss and ericaceous dwarf shrub removals on the composition and diversity (assessed via metabarcoding) and biomass (assessed via PLFA markers) of terricolous lichen communities along a 5000‐year boreal forest post‐fire chronosequence in northern Sweden. Overall, our results showed that shrub removals had a greater impact than moss removals on the biomass and composition of lichen communities. Shrub removals increased lichen alpha‐diversity while decreasing lichen beta‐diversity. This is mainly because, although the number of lichen species increased in the absence of shrubs, lichen communities were strongly dominated by Cladonia spp. However, the effects of shrub removals were context‐dependent, with greater effects observed in older ecosystems. Our results highlight that shrubs had a greater impact than moss in shaping terricolous lichen communities in boreal forests, with increasing effects from young ecosystems to older ones. We conclude that the foreseen expansion of vascular plants such as ericaceous shrubs into high latitude regions will probably have negative consequences on lichen cover, but that these effects will be dependent on the environmental context.