Snags, logs, stumps, and microclimate as tools optimizing deadwood enrichment for forest biodiversity

Abstract

The reduction of deadwood due to forest management threatens saproxylic diversity. Therefore, deadwood needs to be preserved and enriched. While the importance of deadwood tree identity is well investigated, the value of different object types and microclimate for diversity is insufficiently understood. Conservation-oriented forest management, therefore, requires guidelines on how deadwood types under various microclimatic conditions can help to sustain saproxylic diversity. We set up an experiment in sub-montane beech forest to disentangle effects of microclimate (sun vs. shade) and deadwood types (logs, stumps, snags). By surveying beetles, fungal fruiting bodies, and fungal molecular taxa (amplicon sequence variants, ASVs) in early-decomposition stage deadwood, we asked: (i) What is the relative importance of deadwood types vs. microclimate on saproxylic α- and β-diversity? (ii) What is the importance of stumps, logs, and snags for saproxylic α- and β-diversity? (iii) Which combinations of microclimate and deadwood type maximize γ-diversity? Deadwood types had a stronger effect on α- and β-diversity of all groups than microclimate, which was not significant in most cases. Among deadwood types, α-diversity was higher on logs than on other deadwood types for beetles and fungal fruiting species. Fungal ASVs reached high α-diversity on snags. Considering effective combinations of deadwood types and microclimate in their contribution to γ-diversity, shaded and sunny logs showed most importance for beetles and fruiting fungi, while sunny snags were important for fungal ASVs. Maintenance of saproxylic diversity is therefore best achieved via enrichment of different deadwood types and by emphasizing logs and snags under variable microclimates.