Enhanced forest heterogeneity drives stronger functional than taxonomic shifts in soil nematodes

Production forests are often managed primarily for timber production, leading to biotic homogenization and reduced biodiversity. To explore strategies that promote biodiversity while maintaining timber yields, we conducted a large-scale experiment in eight German forests. We manipulated structural β-complexity, i.e., the heterogeneity of structural elements across forest patches, by experimentally introducing variation in canopy gaps and different types of deadwood across 156 plots of 50 × 50 m each, to investigate its effects on forest biodiversity. We analyzed soil nematode communities, which are important bioindicators and contributors to ecosystem processes, by assessing taxonomic and functional diversity across patch (α), site (γ), and between-patch (β) scales using Hill–Chao numbers. Additionally, we tested whether environmental variables explain nematode diversity responses. Our results show that functional diversity is more responsive than taxonomic diversity, with increased β-diversity of common and frequent taxa alongside simultaneous declines in α– and γ-diversity. This pattern suggests a shift toward more specialized nematode communities in response to the intervention. Moreover, we found that site-specific conditions, such as sand content and understory biomass, modulated these effects. Overall, our findings reveal complex, scale-dependent responses of nematode diversity to aboveground forest structural changes, emphasizing the need to consider environmental context in forest biodiversity management. This study represents an important first step toward understanding and enhancing soil biodiversity at management-relevant spatial scales.