Global warming induces new constraints on forest ecosystems and requires forest management adaptation. The reduction of stand density is currently debated in France as a potential tool to face increasing climate change-induced tree mortality risk due to summer drought by improving forest resistance to water stress. Our study aimed to assess the potential impact of this forest management adaptation on soil biodiversity, i.e. the detrital food web, and ecosystem functioning, i.e. litter and soil organic matter decomposition processes. We took advantage of a large-scale, multi-site experimental network of long-term forestry trials experimentally manipulating oak stand density through thinning operations in contrasted stand age and local abiotic context. Our results provide evidence that reducing stand density will have substantial impacts on the detrital food web structure, with cascading effects on soil functioning. While microbial biomass had little response, the effect of stand density on microbial-feeding nematodes was much more contrasted. Microarthropods such as collembolan and oribatid mites as well as diplopoda and anecic earthworms were depleted by stand density reduction. In contrast, endogeic earthworms were beneficially affected. Litter quality and decomposability decreased with stand density reduction while standard litter decomposition increased. Therefore, in situ litter decomposition was lower and carbon sequestration higher at intermediate stand density. Exploratory analysis using causal diagrams, i.e. path analyses, highlighted that those changes were mainly related to understory vegetation, microclimate and soil pH conditions alterations Overall, our study emphasizes that managing stand density of oak forests at intermediate level appears as the best way to optimize the trade-off between improving forest resistance to drought and preserving soil biodiversity and ecosystem functioning.