Influence of forest thinning on the soil fauna: a systematic review of current knowledge and research gaps

Abstract Key message This systematic review shows that thinning effects on soil fauna abundance and species richness vary with thinning strategy and methodological approach. Positive responses are due to improved resources and favorable microclimate conditions, whereas negative responses were mainly associated with unfavorable microclimate conditions. However, current evidence remains fragmented, highlighting the need for standardized, comprehensive experiments to draw robust conclusions and generalize management recommendations. Context As harvesting and reforestation expand to meet bio-economy and renewable energy demands, forests face increasing pressure from both unsustainable practices and climate change. Forest thinning, widely used across many regions, alters forest structure, vegetation and microclimate, leading to cascading effects on soil biodiversity. Yet, compared to microbial communities, soil fauna remains comparatively understudied despite their diversity and central role in ecosystem functioning. Aims We conducted a systematic review to assess how forest thinning influences soil fauna. Results Only 41 articles were identified: 27 focused on macrofauna (170 observations), 20 on mesofauna (96), and 6 on microfauna (13). These experiments varied considerably in their forest thinning strategies, sampling methods and soil fauna metrics, making it difficult to conclude whether soil fauna abundance or species richness respond to thinning in a consistent way. Both positive and negative effects were reported. Reducing forest cover can lead to less favorable microclimatic conditions with cascading negative effects on soil fauna. Conversely, the resulting increase in understory vegetation biomass and diversity caused by forest opening can create more heterogeneous microhabitats and resources with cascading positive effects on soil fauna. Conclusion The observed variability in research approaches limits our mechanistic understanding of soil fauna response to thinning. We therefore emphasized recommendations for future research to improve methodological consistency and the robustness of findings.