Calicioids are a group of lichenized and non-lichenized fungi that are superficially similar to each other in appearance. Many members of this group tend to be restricted to old-growth forests, for which they have been used as indicators. However, the definition of old-growth varies among jurisdictions and forest types. In addition, variables other than tree age, which is often used to define old-growth, have been postulated to be important for influencing the presence of calicioids (e.g., continuity, scale, and ecological and structural variability). These variables, in combination, can be taken to indicate something about forest condition, particularly its ecological integrity. To understand better the ability of calicioids to serve as indicators of forest condition, we recorded the number of species in 51 stands across a chronosequence in Canada's most homogenous forest ecosystem with the most frequent natural disturbance regime; the boreal forest. We restricted our sampling spatially and temporally in stands with similar tree cover and soil type. We recorded the number of species and biomass of all lichens in each stand along with forest stand attributes. We constructed 13 competing models to explain calicioid species diversity and show that stand age is important, but only in combination with stand condition. The strongest positive correlations were between calicioid density and lichen biomass and richness. Therefore, calicioid diversity appears to be a good indicator of habitat condition or conservation value in the boreal forest, which includes continuity. Similar research in other forest types that are more heterogeneous and have longer natural disturbance regimes will help build a better understanding of how calicioids can be reliably used as indicators of forest quality more broadly for conservation purposes.
