Data from: Forest management adaptation to climate change: a Cornelian dilemma between drought resistance and soil macro-detritivore functional diversity

Global warming induces new constraints on forest ecosystems and requires forest management adaptation. The reduction of stand density is currently debated as a potential tool to face increasing summer drought risk by improving forest resistance to climate change-induced tree mortality. However, few studies have yet assessed the impacts of this management change on soil biodiversity. We conducted a large-scale, multi-site assessment of the response of soil macro-detritivore assemblages and soil functioning to experimental manipulations of stand density. A total of 33 stands were studied covering a wide gradient of stand density, i.e. stand basal area from 2.5 to 43.7 m2 ha−1, stand age, i.e. 18–171 years-old and abiotic context. We observed contrasting responses as a function of both taxonomic and functional groupings. Exploratory analysis using causal diagrams, i.e. path analysis, highlights that these changes were mainly related to alterations in understory vegetation, microclimatic and soil pH conditions. The response of soil macro-detritivore assemblages to stand density manipulation was consistent over the gradient of stand ages. Among the litter-dwelling macro-detritivores, millipede abundance and diversity decreased with stand density reduction while woodlice and epigeic earthworms were unaffected. Further, a shift of soil-dwelling earthworm community composition was observed in mull stands. Endogeic earthworm abundance showed a sharp increase with stand density reduction, which translated into an increase of soil respiration. In contrast, anecic earthworm abundance decreased and was strongly associated with a decline of the rate of forest floor turnover. Synthesis and application. Our study provides strong evidence that reductions of stand density will have substantial impacts on soil macro-detritivore assemblages and cascading effects on soil functioning, particularly in mull stands. Managing stand density of oak forests at an intermediate level, i.e. 25 m2 ha−1, appears to be best to optimize the trade-off between improving forest resistance to climate change and ensuring the conservation of functional diversity to preserve forest ecosystem functioning and stability.