Spatial patterns of saproxylic beetles in a relic silver fir forest (Central Italy), relationships with forest structure and biodiversity indicators

The conservation of biological diversity has become one of the important goals of managing forests in an ecologically sustainable way. In the mountainous Mediterranean forest ecosystems, the relationships between forest structural indicators and biodiversity are still poorly studied. Carefully designed studies are required to test relationships between the presence and abundance of potential indicators and the maintenance of critical ecosystem processes in forests. In this study, forest structure, deadwood amounts and microhabitats occurrence were considered indicators for conservation issues at stand level. We described the stand structural attributes, deadwood characteristics and microhabitats occurrence, evaluating their role in influencing the abundance, distribution and diversity of saproxylic beetle fauna. The study was realized in Central Apennines (Italy), in a silver fir forest that has been unmanaged since several decades. A systematic aligned sampling method was realized on 240 ha, examining 50 plots of 530 square meters each. Data were collected to assess forest structural parameters, living and deadwood volumes, and the relative abundance of different deadwood components. Saproxylic beetles were sampled using window flight traps and emergence traps, with the aim of obtaining data on abundance and species richness at plot level, but also on decaying deadwood. The heterogeneity in types and frequency of microhabitats, and the link between structure-based indicators and saproxylic species were also analysed. The linear regressions was conducted for highlighting the variability of the parameters investigated and their relationships. Geostatistical analyses were also conducted in order to highlight the spatial variability of the structural features and the beetle pattern distributions. Results showed how the saproxylic beetles community is influenced by the deadwood amounts, size and decay, but also by the forest complexity and microhabitat occurrence. Gaps dynamics and natural disturbances had effects on deadwood amounts and microhabitat abundance, which was significantly higher than in managed and structurally simplified forest stands. With the aim of describing the complex saproxylic ecological network, the species of beetles were classified according to the type of interactions with wood and other insects, but also in relation to the trophic guilds.