Bryophytes and lichens in different types of forest set-asides in boreal Sweden

Setting aside forest land is practiced globally and is of vital importance to the preservation of forest biodiversity. As detailed species inventories rarely precede the establishment of set-asides, empirical studies on the species content of different set-aside types are needed, in order to evaluate their conservation relevance and to design efficient conservation strategies. Here, we compared the biodiversity value per unit area of three types of set-asides, common in boreal Europe: nature reserves, key habitats and retention groups on clear-cuts, and we also included old managed forests as reference sites. We surveyed bryophytes on all substrates and lichens growing on spruce in spruce-dominated forests in middle boreal Sweden and in total 252 bryophytes and 176 lichens were found. For bryophytes the number of species, as well as the number of red-listed species, per unit area was higher in key habitats than in retention groups and old managed forests, while intermediate in nature reserves. As the complementarity between areas was greatest in key habitats, the total number of bryophyte species found was by far the highest in this set-aside type. For lichens the patterns were similar but the differences much less pronounced. Site selection methods based on linear programming demonstrated that key habitats also played the most important role in representing the surveyed taxa effectively but that the value of nature reserves increased when multiple representations of each species were required. The study shows that the richness and composition of bryophytes and lichens differ between the three set-aside types and consequently, the outcome of large-scale conservation strategies based on anyone type would be different. At present, key habitats stand out as core areas of high diversity in the forest landscape but it is important also to acknowledge the temporal dynamics of the forest landscape and how the capacity of each set-aside type to host species can be expected to change over time.