How to make deadwood? Comparing the effects of practical artificial deadwood enrichment techniques on early-arriving saproxylic beetles in Scots pine plantations

Much of the biodiversity of forest ecosystems depends on the abundance and diversity of deadwood, which is often scarce or absent in commercial forests. Deadwood enrichment is a commonly used intervention for restoring saproxylic biodiversity, but how effectiveness of deadwood enrichment techniques – such as girdling, felling and uprooting – for biodiversity restoration relate to each other is poorly researched. This study aimed to experimentally assess how attraction of saproxylic beetles (Coleoptera) differs between different deadwood enrichment methods. We used flight interception traps to compare attraction of saproxylic beetles between seven methods of tree damaging and killing, replicated in a randomized block design in dead-wood deficient Scots pine ( Pinus sylvestris ) plantations in the Netherlands. We compared saproxylic beetle richness, abundance and assemblage composition. In total 163 saproxylic beetle taxa from 57 families were collected. All deadwood enrichment treatments attracted a higher saproxylic beetle abundance and richness than vital control trees. Abundance of beetles attracted was lower for treatments involving sub-lethal damaging than for treatments involving instant tree death. Snagging trees, girdling or creating high- and low stumps was more effective than girdling or uprooting trees, while damaging trees had little effect. Beetle richness and abundance varied across time during the sampling season. The species assemblage composition of saproxylic beetle communities also differed between treatments. Overall, the early-decomposer beetle communities attracted to deadwood objects created by manual felling or damaging are mainly dominated by common species associated with conifers. The results of our study suggest that early attraction of saproxylic beetles to deadwood substrate is driven by a combination of primary attraction and random landing strategies. These findings suggest that certain deadwood creation techniques show greater promise for boosting the biodiversity in tree plantations. Because of the unique associations attracted to certain techniques, stronger short-term effects on attracted beetle richness and abundance are achieved by combining techniques – by including girdling, uprooting and creating (snagged) high- and low stumps, but not by sublethal damaging.