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

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 alpha- and beta-diversity? (ii) What is the importance of stumps, logs, and snags for saproxylic alpha- and beta-diversity? (iii) Which combinations of microclimate and deadwood type maximize gamma-diversity? Deadwood types had a stronger effect on alpha- and beta-diversity of all groups than microclimate, which was not significant in most cases. Among deadwood types, alpha-diversity was higher on logs than on other deadwood types for beetles and fungal fruiting species. Fungal ASVs reached high alpha-diversity on snags. Considering effective combinations of deadwood types and microclimate in their contribution to gamma-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.

Automated summary

The reduction of deadwood due to forest management threatens saproxylic diversity. Deadwood types have a stronger effect on alpha- and beta-diversity than microclimate, with logs showing higher diversity for beetles and fungal fruits, and snags having high fungal diversity. Effective combinations of deadwood types and microclimate contribute to gamma-diversity.