Abstract

Climate change is expected to profoundly affect forest biodiversity, yet its impacts on saproxylic and non-saproxylic insects remain largely mediated by forest structure and management. Saproxylic beetles strongly depend on tree-related microhabitats (TreMs), which reflect stand development, deadwood dynamics, and habitat continuity. In this study, we assessed how future climate change may influence saproxylic beetle richness and TreM diversity across the Italian Apennines by integrating long-term field data from 336 forest plots with machine-learning models and the process-based forest model 3D-CMCC-FEM. Beetle and TreM richness were projected under a baseline current climate scenario (CCS) and two future climate scenarios (RCP4.5 and RCP8.5) until 2100. Gaussian process regression models with strong extrapolation performance were used to forecast richness trajectories based on simulated forest structural and climatic variables. Results show that host tree species and stand structural development are the primary drivers of both beetle and TreM richness, while differences among climate scenarios are comparatively small. Richness trajectories differed markedly among forest types: beech stands showed temporary mid-century increases under climate change scenarios, chestnut forests remained relatively stable, and silver fir and Turkey oak stands exhibited long-term declines or convergence toward lower richness levels. Patterns of TreM richness closely mirrored beetle richness, highlighting the central role of structural complexity and microhabitat availability. Overall, the effects of climate change on beetle diversity appear to be largely indirect, acting through forest growth, mortality, and microhabitat dynamics rather than through direct climatic constraints. These findings emphasize that forest management practices maintaining structural heterogeneity and microhabitat continuity can substantially mitigate climate-driven biodiversity changes, supporting the integration of TreMs into climate-adaptive forest management strategies.

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