Below-ground biodiversity in organic agroforestry with free-range pigs in Denmark

Integrating biodiversity into agricultural systems, particularly through agroforestry, is increasingly recognized as an important step to achieve sustainable land management and soil health. Free-range farming, where animals are allowed to interact directly with their environment, may add benefits to soil ecosystems. In this study, we investigated how free-range pig farming, combined with agroforestry elements, influences belowground biodiversity, including microbial communities comprising prokaryotic, fungal and invertebrate communities. Prokaryotic, fungal, and invertebrate diversity were assessed using environmental DNA (eDNA), while earthworm density was measured via conventional method of hand sorting to obtain abundance measures. Soil samples were collected from two organic pig farms with differing agroforestry tree compositions and different periods with pigs in the fields. Our results showed that the presence of pigs was associated with the shifts in soil biodiversity, with contrasting responses observed across prokaryotes, fungi, and invertebrates, suggesting that free-range pig systems integrated with agroforestry practices can have complex, taxon specific effects on soil ecological diversity. In addition, tree age, species composition, and tree richness significantly impacted the soil microbial and invertebrate community composition. Earthworm abundance was generally negatively affected by the pig production system, and our results indicate that periods of undisturbed grass-clover cover, without pig activity, had a positive effect on the earthworm community.