Epiphytic lichen biomass in managed and old-growth boreal forests: Effect of branch quality

To maintain biodiversity in managed forests we must understand the patterns and processes that regulate the occurrence and dynamics of species in undisturbed ecosystems. We compared biomass and species composition of canopy lichens on 180 lower branches of Norway spruce (Picea abies) in three pairs of old-growth and managed (selectively logged) stands in northern Sweden (30 branches per stand). The purpose was to evaluate the effect of substrate quality (branch characteristics) on patterns of lichen biomass for two different growth forms (foliose and fruticose). Old-growth stands had six times higher lichen mass per spruce branch, and two times higher expressed as percentage of branch mass, compared to mature stands of managed forest. Lichen mass was strongly related to mass, diameter, and age of branches. Fruticose, pendulous species (Alectoria sarmentosa and Bryoria spp.) were highly sensitive to forest practices. In contrast, type of forest had no significant effect on foliose species. Species number per stand was the same (15 species) in both types of forest, but there were marked differences in the relative abundance of different lichen groups. Results suggest that limited amount of substrate (i.e., small branches) available to lichens, and young branches, providing only a short time for lichen colonization and growth, are important factors limiting epiphytic lichen abundance in managed forests. Conversion of old-growth forest into young, managed stands will lead to a significant reduction in epiphytic lichen mass. This in turn may probably affect nutrient cycling in forests and has negative consequences for animals that utilize canopy lichens as food, shelter, or nesting material.