What is good for birds is not always good for lichens: Interactions between forest structure and species richness in managed boreal forests

Tree species identity and composition shape the epiphytic lichen community of structurally simple boreal forests over vast areas

“…In the modified MMf, the half saturation parameter is replaced by true beta diversity [49] and the unit at which alpha diversity (number of lichens on an average tree) is evaluated (Details on the modified MMf are in the S1 File). In this study, we assume species accumulation would become asymptotic long before all trees per stand would be sampled because an average forestry stand in Sweden (4.5 ha [27]) of the type we study contains far less lichen species than trees (500-1000 trees per ha with an average stem diameter of~20 cm [24]). In this study, the parameters of the modified MMf (Eq 2) are therefore a measure of expected between tree beta…”

“…and oak Quercus robur (L.). On the established 59 plots (50 m radius), we surveyed a 10 m radius subplot for the lichen inventory, whose location was randomly chosen either at the centre or 25 m to the east or west of the centre of the plot (for details on plot placement, selection and forest metrics consult Klein et al, 2020). In May 2018, a lichenologist (GT) noted the presence of all lichen species within 2 m above ground on the trunk and the branches separately on every living tree (dead branches included) with a diameter at breast height (DBH) >10 cm.…”

“…For each tree we knew the tree species and DBH (used for the tree level model) and the subplot's tree species composition and average stem DBH (used for the stand level model). For details on lichen species determination and nomenclature consult Table A.2 in Klein et al [24]. A reference collection of the majority of species observed in this study can be found at the UPS herbarium at Uppsala University, Sweden.…”

“…However the fact that the DBH was important in the model with tree species richness suggests that a larger DBH can lead to a higher lichen richness in forests with uneven tree species frequencies. It is also probable that other factors associated with specific tree species, such as how they affect light penetration into the lower levels of the forest or how they affect each other's bark pH due to runoff connected to rain, also play a role in these relationships [24,59]. That beta diversity was largely negatively affected by the average DBH, indicates that, as more and more different lichen species start to grow on trees with an increasing DBH, many trees also start to host the same species more frequently.…”

“…In the context of this study they can be used as a biodiversity indicators [22,23]. Forests that host a high lichen diversity are also expected to host a high diversity of other organism groups through a shared requirement for key structural elements (but see [24]). Although there is evidence that epiphytic lichen diversity in boreal forests is related to the tree species composition (e.g.…”