Drivers of community assembly change during succession in wood-decomposing insect communities

1. The patterns of successional change of decomposer communities is unique in that resource availability predictably decreases as decomposition proceeds. Saproxylic (i.e., deadwood-dependent) beetles are a highly diverse and functionally important decomposer group, and their community composition is affected by both deadwood characteristics and other environmental factors. Understanding how communities change along faunal succession is important as this process influences terrestrial carbon dynamics. 2. Here, we evaluate how beta-diversity of saproxylic beetle communities change with succession, as well as the effects of different major drivers of beta-diversity, such as deadwood tree species, spatial distance between locations and forest structure. 3. We studied spatial beta-diversity (i.e., dissimilarity of species composition between deadwood logs in the same year) of saproxylic beetle communities over eight years of wood decomposition. Our study included 379 experimental deadwood logs comprising 13 different tree species in 30 forest stands in Germany with differences in forest structure that is influenced by management regimes. We hypothesized that the effect of tree species dissimilarity, measured by phylogenetic distance, on spatial beta-diversity decreases over time, while the effects of spatial distance between logs (1m to ~600km) and differences in forest structure increase. 4. Spatial beta-diversity of saproxylic beetle communities was high throughout the first eight years of succession and even increased slightly over time except when focusing on dominant species (i.e., q = 2 in the Hill number calculation). Beta-diversity increased with increasing phylogenetic distance between tree species, spatial distance, and differences in forest structure. While effects of space and forest structure were constant over time, the effect of phylogenetic distance decreased over time. 5. Our results show that the strength of the different drivers of saproxylic beetle community beta-diversity changes along deadwood succession. Beta-diversity of early decay communities was strongly associated with differences between tree species. Although this effect decreased over time, beta-diversity remained high throughout succession. Possible explanations for this pattern include differences in decomposition rates and fungal communities between logs or the priority effect of early successional communities. Our results suggest that saproxylic beetle diversity can be promoted by high diversity in tree species and forest structural characteristics.