Can 'continuity indicator species' predict species richness or red-listed species of saproxylic beetles?

Abstract

This study investigates the relationship between the abundance of wood-rotting fungus suggested as 'continuity indicator species' and environmental variables for the assemblage of saproxylic (wood-living) beetles associated with Fomitopsis pinicola fruiting bodies in a mature spruce forest in southeastern Norway. The presence of species thought to indicate continuity in old growth is one of the criteria used when finding and delineating small protected areas ('woodland key habitats') in Scandinavian forestry. Although it is clear that remnants of old-growth forest are important for many taxa, documentation as to which entities or species the indicator species indeed indicate is scarce. If stands with a continuous and unbroken input of dead wood have a unique assemblage of wood-rotting fungi, it seems relevant to ask if these stands also have a unique assemblage of rare saproxylic beetles. I find that the indicator species exhibit no significant correlations with beetle species richness or with the presence of red-listed saproxylic beetles as a group. The different characteristics of dead wood conditions are the most important environmental variables that explain both the species richness and the presence of red-listed beetles. Single-species analyses reveal contrasting relationships. The red-listed beetle Atomaria alpina shows a significant and positive association to the abundance of indicator species. Contrary, a group of three red-listed species with similar ecology in the family Cisidae exhibits a significant and negative association to indicator species abundance. This indicates that important patterns are concealed when considering general measures such as overall presence of red-listed beetles. Single-species studies are necessary in order to correctly understand how rare beetles respond to forestry activities and to develop a policy that can secure their continuing existence in the boreal forest.