Survey of saproxylic beetle assemblages at different forest plots in central Italy

Saproxylic beetles from coarse deadwood debris found on the forest floor were documented for the first time at four permanent monitoring plots in central Italy that are part of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). The plots consisted of unmanaged vegetation communities representing typical beech forest, mixed broadleaf and conifer forest, Turkey oak forest, and cork oak forest respectively. With the present study, we identified beetle assemblages to species level and investigated whether the type of vegetation affects beetle communities. In order to detect more of the species present and perform a better comparison among study sites, samples were collected with two types of traps: flight interception traps hanging from tree branches (n = 1 per plot) and emergence traps mounted on deadwood like fallen branches or trunks (n = up to 8 per plot, depending on the availability of deadwood pieces). A total of 1372 individual beetles, belonging to 133 species of 36 families were captured, identified and enumerated. Considering all beetles caught in both trap types, alpha-diversity values indicated high beetle diversity at all of the four forest sites, while measured species richness, accumulation curves and species richness estimators agreed that the highest species density was at Rosello. Monte Rufeno had the highest abundance of beetle individuals. Monte Rufeno and Monte Circeo had the highest numbers of saproxylic species, even though Rosello had the highest total number of beetle species. Ninety species (67.7% of the species found in all plots combined) were caught in only one plot, while only three species, representing 2.3% of the total of species, were collected at all of the four plots; nine saproxylic species were collected exclusively at Monte Circeo, among them rare singletons like Agrilus convexicollis mancini Obenberger (Buprestidae) and Nematodes filum (F.) (Melasidae), the latter recorded in central Italy for the first time. Environmental variables having the strongest correlations with the assemblage composition were plot-scale variables (slope, stand age, amount of deadwood). The only trap-scale variable that showed up as related to assemblage composition was wood decayclass. The study highlighted that the diversity in saproxylic beetle communities reflects the different tree communities at the four study plots. The research also showed that even at the small and very small scale of forest plots, traits of beetle assemblages can be revealed on coarse deadwood debris.