Recovery of soil macrofauna in Amazonian secondary forests is driven by vegetation complexity rather than fallow age alone

In the Amazon, shifting cultivation has historically shaped the landscape and remains a key land-use system practiced by traditional communities. The ecological sustainability of this system depends on the regeneration capacity of forests between cultivation cycles. In this study, we investigated mechanisms regulating the recovery of soil macrofauna during natural regeneration of areas previously managed via slash-and-burn agriculture, evaluating the effects of fallow age, environmental variables, and trophic interactions on macrofauna diversity and community composition. We sampled 40 plots along a successional gradient from 1 to >80 years and collected soil and vegetation data. We used structural equation modeling, generalized additive models, and multivariate analysis to understand observed patterns. Fallow age did not directly affect macrofauna but exerted an indirect effect through vegetation. We also observed a top-down effect of predators on herbivores, detritivores, and geophages, highlighting the role of trophic interactions in structuring soil communities. These findings reinforce that sustainability of shifting cultivation should not be assessed solely on fallow age or vegetation cover but on the capacity of the regenerated system to sustain ecological functions. Given effective vegetation regeneration and a landscape favoring ecosystem resilience, this traditional land-use system can contribute to biodiversity and soil functionality restoration.